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Optical storage technology : applications and implications for archives Kovacs, Judith Susanna 1994-03-04

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OPTICAL STORAGE TECHNOLOGY:APPLICATIONS AND IMPLICATIONS FOR ARCHIVESbyJUDITH SUSANNA KOVACSB.A. (Hon.), Trent University, 1986M.A., Queen’s University, 1989B.Ed., Queen’s University, 1990THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF ARCHIVAL STUDIESinTHE FACULTY OF GRADUATE STUDIESSchool of Library, Archival and Information StudiesWe accept this thesis as conformingto the required standardUNIVERSITY OF BRITISH COLUMBIAOctober 1994© Judith Susanna Kovacs, 1994Signature(s) removed to protect privacyIn presenting this thesisin partial fulfilment of the requirements foran advanceddegree at the University of BritishColumbia, I agree that the Library shall makeitfreely available for reference and study.I further agree that permissionfor extensivecopying of this thesis for scholarlypurposes may be granted by thehead of mydepartment or by his or her representatives.It is understood that copying orpublication of this thesis for financialgain shall not be allowed withoutmy writtenpermission.(Signature)________________________Department ofLl9 C/L1 cJThe University of BritishCo umbiaVancouver, CanadaDate________DE-6 (2/88)Signature(s) removed to protect privacy11ABSTRACTOptical storage technology has advanced to the point where onecan store megabytes and terabytes in a very small physical space. The use ofthisform of mass electronic storage has the potential to affect the way archivesconserve, preserve, store and make accessible the records in their custody.Thus, it is important for archivists to understand not only the technology, but theimplications of its use on traditional archival methods and practices.This study provides a description of the technology, conservationand preservation issues, and archival implications involved in the use of threeoptical storage systems: WORMs, Rewritables, and Optical Tape. Some of thetechnological, legal and archival problems associated with the use of thesesytems by archival programs or institutions are discussed, and a few case studiesinvolving the use of optical storage systems in archives are presented.This thesis concludes that, while there are problems associated withthe use of optical storage systems as archival conservation and preservationtools, the advantages presented by these systems outweigh their disadvantages.111TABLE OF CONTENTSABSTRACT iiTABLE OF CONTENTS iiiACKNOWLEDGEMENTS ivINTRODUCTION 1CHAPTER ONE: The Technology 13WORM Technology 14Rewritable Technology 30Optical Tape 40CHAPTER TWO: Preservation of Optical Media 45Media Degradation 50Storage and Handling 63CHAPTER THREE: Optical Storage Media:Archival Applications and Implications 74Applications 75Migration 78Preservation and Access 82Implications 89CONCLUSION 91Advantages 91Disadvantages 93Consequences for therole of the archivist 94BIBLIOGRAPHY 96ivACKNOWLEDGEMENTSOnce more unto the breach, dear friends, oncemore...(Henry V, act 3, Sc. 1, lines 1-2)In many ways, writing this thesis hasbeen a battle, one which I could not havesurvived without the helpand support of my friends. There were many, manydays when I did not knowif I was ever going to see the end of this, butsomehow my friends managed to getme to see this thesis through to itsconclusion. I’ll bet they’re happier to seethis thing over with than I am. I owemany thanks to the people who put upwith me and my thesis angst these pasttwo years. Here goes - (in noparticular order) thanks to: Luciana Duranti foragreeing to supervise this thesis and giving methe criticism and support mythesis and I needed; the J-Club for the pool,Grad Centre visits and listening tome whine about life, the universe and thisthesis; friends at VST for actuallypaying attention to my “nap time” sign; Bruna, Lyndonand Gerald for their email; Anne for those 2-hour phone calls to Ontario; andmost of all Andrea,Heather, Doug, and Ian for putting up with meduring my thesis-writing angst,The Hard Drive That Ate My ThesisCrisis, wingeing about WORMs, and forboosting my flagging self-confidence on those innumerabledays when I did nothave any confidence at all. Thanks folks.I promise never to put any of you ormyself through this ever again. And I reallymean it this time.1iNTRODUCTION“But without any doubt, optical storage in one form or anotherwillbe playing an increasingly important part in the computersof thenext decade and beyond.”1In the fi.iture, people will take for grantedboth instant access toand compact storage ofvast amounts of information.Present day technology isquite advanced in that respect. Optical storagetechnology has progressed to thepoint where megabytes and terabytes of informationcan now fit almost into thepalm of one’s hand. While the use of this technology bringsforth some problemsand issues involving both the technology and applicationof archival theory, thenatural data permanence ofWORM (Write OnceRead Many times or WriteOnce Read Mostly) disk systems in particular offers somevery practical solutionsto today’s archival storage, maintenance and information needs.Thereforearchives and archivists must learn how to use optical storage technologyto thefull benefit of both the records and their users.Compared to that of many office informationprocessing products,optical disk technology has a relatively long history. Unlike personalcomputers,Local Area Networks (LANs), document scanners and fax machines, the opticaldisk has been around since the 1 970s, being just one medium in a long line ofelectronic devices used to read and store encoded information. Devicessuch as1A. Bradley, Optical Storage for Computers: Technology and Applications,(Chichester, UK: Ellis Horwood Ltd., 1989), p. 191.2the photoelectric readers used to read punched cards, and the Hollerith cardsinitially used in the 1890 United States census were the beginning of thedevelopment of machine- oriented data storage devices. Although these earlyforms of data storage were of the non-eraseable variety, they were an expressionof the technology ofthe day, rather than of user preference, and required boththe user and the computer systems to adapt to and ultimately accept the conceptofwrite-once data storage.It did not take long, however, before user storage needs andtechnological development combined to produce a storage medium which hadincreased capacity and, eventually, eraseability. By the 1950s, the developmentof a reliable magnetic data storage medium not only was a significantimprovement in both storage capacity and reliability, but over time offered theadvantage of data erasure. Nonetheless, the practical limits of magnetic storagedensity started to become evident in the 1970s, and optical media began to bedeveloped as the next generation of storage media.Research on optical disk technology began in the early 1970s, andinitially concentrated on the development of WORM technology. Once again,this was a function of the technology ofthe time rather than a consequence ofthedemands ofusers. WORM drives and media were introduced in the early 1980s,and became commercially available a few years later.2 Extremely high-densitystorage was accomplished in 1989 with the introduction of optical tape- basedsystems. Optical tape is a high-density WORM-based storage medium with a oneterabyte storage capacity on a 880m by 3 5m tape. The tape itself fits onto a12”reel.3 These products, however, were not meant to be the final formats for2w Saffady, Optical Storage Technology 1992: A State of the Art Review,(Westport, CT: Meckler, 1992),p.4.3D. Pountain, “Digital Paper”, 14:2 (February 1989),p.276.3optical storage media, but rather development tools from which erasable storage,the ultimate and potentially more commercially acceptable goal, would emerge.The goal of producing rewritable optical disk systems was reached in 1988, when5.25” rewritable optical disk systems were made available to consumers. Higher-density 3.50” disks have since become available, and integrated WORM andrewritable systems are just coming onto the market. The development ofrewritable disk technology did not sound the death knell for WORMs, however,as they had developed their own niche in the information storage world. Futureresearch and development will probably lead to both WORM and rewritablesystems with even greater storage capacities in even smaller physical spaces.The first efforts in the development of high capacity opticalstorage, however, focussed on photographic media, as “these were welldeveloped and understood, and high resolution materials were alreadyavailable.”4Experiments using photographic film to create a mechanism whichcould enable digitally-encoded data to be written on a medium at a high density,to be retrieved later at a relatively high speed were initially performed atInternational Computers Limited (ICL). These experiments resulted in a devicewhich employed a light beam that moved horizontally over photographic film.Data was written on the medium by turning the light beam on to record a “1” bitand turning it off to record a “0” bit. Once the film was developed, a permanentrecord of the data recorded on the medium was created. The data was retrievedby using the same light beam, this timeleft on, in conjunction with aphotodetector to sense the changes in lightintensity as they passed through thefilm. The necessity for a processing stagebetween the writing and reading ofinformation on the film resulted in a read-onlystorage medium rather than a true4Bradley, Optical Storage for Computers,p.181.4WORM-type device. Although this particular device nevermade it past theexperimental stage, it did introduce the idea of using changes in light intensity asa means by which information may bewritten on and read from a data storagemedium.5A similar system was produced and sold commercially byInternational Business Machines (IBM) under the name Photochip. Itrecordedinformation onto a glass plate, then loaded it into a jukebox-like machine whichallowed the information to be read at special reading stations.6Althoughthissystem was not commercially, it set the stagefor future commercialdevelopment of optical storage devices. The Photochip system also showedthathigh-density storage was not a pipe dream, but would soon be available.Holography was the next stage in the developmentof opticalstorage technology. In the early 1970s, experiments were performed using theprinciple of “interference between light beams” as a basis for infonnation storage.In very simple terms, holography is based on the idea that light beamsfrom everypoint in the source combine to produce all the points in the image. These arecalled interference patterns and they hold all the information needed to reproducethe source from the image. If one can reproduce the “interference patternand alight source identical to just one of those used to create the pattern... it ispossible to recreate an image of all the light sources which produced the pattern.An interference pattern with this property is called a hologram.”7Thisability toreproduce the source, even though part of the originalimage was missing, was astrong selling point for holography-based data storage,as it would allow data toIbid.p.181-182.6p3p.182.7thid,p.196. A much more comprehensive, yet relatively easilyunderstandable, description of holography is presentedin Appendix 2 ofBradley’s Optical Storage for Computers.5be recorded on imperfect media, yet suffer only a loss in contrast and brightnessof presentation, not of data when the data were reproduced for reading purposes.Although systems based on this form of optical storage technologynever actually reached commercial production, a few research prototypes werecreated. In the late 1970s, a “cross between microfiche and computer datastorage” called Mnemos was developed which stored photographic images on arotating disk.8 Mnemos took advantage of holograms’ ability to reproducerelatively intact sources even when part ofthe original image is unreadable orabsent, by using smaller images than those used on microfiche. This greater errortolerance allowed a 12” disk to hold several thousand images, as less room wasneeded for the individual images to be stored. Unfortunately, the reducedsize ofthe images necessitated the use of very powerful laser light sources and highdefinition film for the disk, thus creating a system which was too demanding andexpensive for the technology and the markets ofthat time.9A similar product was created by Holofile, an American firm.Holofile also employed a photographic medium, but utilized a standardmicrofiche sized flat film, rather than a disk shaped storage medium. TheHolofile product used a “two-dimensional array of light sources, . . . called a pagecomposer, [which] had 100 x 100 elements, and the patterndisplayed by it wasrecorded as a single hologram.” The microfiche-sized film had a recordingcapacity of 20,000 holograms, orthe equivalent of approximately 25 megabytesof storage.’° Holofile did not produce a commercialversion of its product, asboth the page composer and the high-poweredlaser it needed to read therecorded images were too expensive and too unreliablefor the product to be8Ibid,p.182.9Ibid,p.182.10Ibid,p.182.6commercially viable.11Although neither Mnemos or Holofile’s product ever becamecommercially available, these two products demonstrate that the leap from purelyexperimental optical storage technology to research prototypes had been made.Optical storage was still far from the commercial marketplace, but prototypescreated with commercial applications in mind were being developed, and this factplaced optical storage technology one step closer to creating a commerciallyviable product. At this point, all that was required to complete the process wasfor optical storage technology to evolve a little fi.irther to the point wheremarketable products would be created from the earlier prototypes.The next step in the development of optical storage technologyinvolved the marriage between holography and photochromic media. In the late1970s, the Plessey Company, in the United Kingdom developed an opticalstorage medium based on photochromic principles similar to those used insunlight-sensitive sunglasses. The film used in the storage medium becameopaque when exposed to one specific wavelength of light, and revertrd to clearwhen exposed to another specific wavelength. Data were recorded on the light-sensitive medium by gas-filled lasers which acted as these light sources. Thelight-sensitive film was then placed on a clear substrate similar to that used forcinematic film tapes. Plessey’s product also allowed for the use of aphotographic emulsion rather than a photochromic medium, but this turned theproduct into a read-only rather than a WORM storage medium. Holographicoptics were used to overcome the problemof media defects and to make the“location ofthe tape relative to the optical headless critical.”2As a result,holograms could overlap each other without a critical loss of data when the11Ibid,p. 183.12Ibid,p.183.7recorded images were recreated. Unfortunately, the “low sensitivity of thephotochromic material and the high cost oflasers of the right wavelength” madethe commercial success ofPlessey’s product unlikely, and the project wasabandoned.13 Although Plessey’s use of gas- filled lasers was an advance inoptical technology, the unreliability of and the expense connected with multiplelight sources forced developers to search for other ways to produce high-capacityoptical storage media.By the late 1970s, it had become evident that, in order to developa commercially viable high-capacity optical storage medium, research anddevelopment would have to break away from photographic technology. The firstproduct to do this was the Unicon, marketed by Precision Instruments. TheUnicon introduced the now commonplace ablative method of encoding data byadapting the write laser to burn holes into a “very short wide polyester tapecoated with a thin metal film”. As with today’s ablative techniques, a burnt holerepresented one binary symbol, and a blank space represented its opposite. Torecord the next track, the laser was moved a short way across the tape, then thewriting process was repeated. A typical model stored “800 megabytes with adata rate of 1 megabyte per second and average access time 8 seconds.” TheUnicon had moderate commercial success; it was particularly attractive to oilcompanies who utilized its high data storage capacity for the recording of seismicdata.14Regardless of its modest commercial success, as a high densityoptical storage medium, the Unicon representedthe first break away fromphotographic technology towards the utilization of the ablative method ofrecording data that is used in today’soptical storage media. Although the13Bradley, Optical Storage for Computers, p. 183.14Ibid,p.183.8developers’ main goal was still the creation of rewritable media, the Unicondemonstrated that there was indeed a market for WORM-based high density datastorage media, leaving the road free for more research and development in thisarea.The successes and failures ofthese various experimental andcommercial ventures, however, led researchers and developers to conclude thatconventional rather than holographic optical disk technology would be thepractical, commercially successfiul way of the future. Systems using conventionaldisk-shaped media would not only be able to provide acceptable data rate andaccess times, but would be able to access the data written to the disk usingmechanical means which are less expensive and more reliable than those used byphotographic and holographic systems.Other optical disk-based systems also had a significant direct andindirect effects on the development of information storage systems. Thedevelopment ofthe videodisk in the late 1970s affected the optical storageindustry indirectly by generating the development of less expensive, morepractical and reliable lasers, optical detectors, servo tracking and focus systems.The development and commercial success of Compact Audio disks and CompactDisc-Read Only Memory (CD-ROM), particularly their use of semiconductorlasers, also directly enhanced the evolution and advancement of optical storagetechnology.Nonetheless, an issue which needed to be addressed was the needfor reliable, defect-free optical media. The actual elements involved in thephysical creation ofthe disks were not necessarily at issue, although oxidation ofthe substrates was an early problem, but rather that high- density data storageallowed for a very small margin when it came to defects which arose during thedata-writing stage. Data are packed so closely on opticalmedia, that a single9physical defect can destroy many nearby data elements. This problem wasrelatively new, as on magnetic media the data elements are much bigger andspaced more widely, thus allowing for a much larger tolerance for media defects.While holographic technology seemed to be a solution to this problem because ofits high capacity to tolerate media defects without affecting the reproduction ofdata, the industry’s inability to produce a commercially viable product hinderedthis approach. Japanese manufacturers attempted to solve this problem by usingbit-mapped images, as they took “advantage ofthe high degree of redundancycontained in written text” and utilized the human eye and brain as a errorcorrection system.’5 Nonetheless, while this system was used somewhatsuccessfully in Japan, it did not enjoy the same success in North America.Ultimately, the problems connected with making defect-free optical media weresolved by the development of powerful error- correction codes.Error correction codes had been use in magnetic storage systemsfor a considerable length oftime. However, those codes demanded by lower datadensity magnetic storage media were not very powerful, as defects would onlyusually affect a few adjacent data elements, rather than many, as it was happeningwith high-density optical storage. If data errors were found in magnetic storagesystems, the data were normally rewritten on a different part of the tape or disk.While such data redundancy would not seem to be a problem with the greaterstorage capacity offered by optical disk storage, nonetheless, complex errorcorrection algorithms were developed which reduced the amount of dataredundancy originally thought necessary. The processing capabilitiesdemanded by these error correcting codes had become more readily and lessexpensively available, thus making it easy to provide these codes at a level which15Thid,p.185.10was acceptable to the vast majority of customers andwould allow more data tobe stored on the disks correctly.The standard error rates of today’s opticalstorage media are as follows:“detected but uncorrected:not more than 1 in1012bits read;undetected errors:not more than 1 ini014bitsread.”Roughly speaking, this is the equivalent ofone uncorrected error a year, or oneundetected error in 100 years.’6The goal of optical disk research, the rewritableoptical disk, wasreached in 1989 with the introduction of a 5.25”rewritable disk. The dominantmethod of recording is Magneto/Optical (MO),a combination ofmagnetic andoptical recording technologies, but phasechange and dye- polymer have beenintroduced in a limited fashion.While they have not yet posed a seriouschallenge to magnetic media, it is not unreasonableto assume that rewritabledisks will eventually develop to the stagewhere this will be a likely situation.WORMs, however, still have a higher storagecapacity, and although this is alsolikely to change in the future, their non-eraseabilitywill still have applications forarchival purposes.It is not possible to predict what path thetechnology of the futurewill follow. Nonetheless, it seems quitecertain that optical storage technology inits various forms will continueto develop, and that it will become morecommonly used as an informationstorage medium. Today’s society is becomingmore and more information- oriented,not only as a gatherer of information, butas a storer of it. The people livingin the information age are increasinglydependent on easy, quick access toinformation from a wide variety of sources.16Ibid,p.33.11They want information fast and they want it all. Because of our needs, opticaldisk based storage systems will probably play an increasingly crucial role in thecomputer systems of the fI.iture, if not for their ability to store vast amounts ofinformation in a small space, then for their relatively easy physical storagedemands. Therefore, it is essential that archivists, as preservers andcommunicators of societal records, understand the characteristics of this storagemedium and the ways in which they can use it to the best advantage of those theyserve.The overall aim of this study is to familiarise the archivalcommunity with the concept of optical storage technology and with the use of itsproducts as conservation and preservation tools. Various kinds ofopticalstorage systems currently available on the North American market will bedescribed, the advantages and disadvantages offered by each type of system willbe outlined, and the conservation and preservation requirements of opticalstorage media will be presented. This illustration will focus on WORMs,Rewritables and Optical Tape only, as these forms of optical storage media arethe most applicable to large-scale archival purposes. They have been chosenbecause unlike CD-ROMs which are Read-Only devices, WORMs, Rewritablesand Optical Tape have the ability to write new data to their respective media.Although CD-ROMs have their uses as portable database storage media, theinherent new data storage capacity ofWORMs, Rewritables and Optical Tape ismore suitable to the record keeping activities of public and private agencies, witha fi.inction similar to that of a high- performance hard disk drive.This study will then examine some of the problems, bothtechnological and archival, which may derive from the use of optical disk systemsto both archivists and records creators. The legal issues associated with thestorage of records on optical storage systems, and the preservation of both12records on optical disks and the disks themselves will be discussed along withbrief examinations of a few case studies involving the use of optical storagesystems in various archives. The ultimate purpose ofthis study is toclariiiquestions regarding optical storage technology itself, its possible and presentarchival applications, and some of the issues and problems presented by storingrecords on this medium.13CHAPTER ONE:THE TECHNOLOGY“Optical storage: a technology in which stored datais read byoptical means.”’Optical disk storage media are not much different from magneticstorage media. Both come in disk and tape forms,and both are used for thepurpose of storing and retrieving information. Where the two systemsdiffer is inthe way the information is stored and retrieved, and ultimately in thecharacteristics ofthe systems needed for its storage and retrieval.Optical storage technology, as its name implies, utilizesopticalmeans to read stored data. The optical means is a laser thatdigitally encodes bitsof information by producing transformations in the medium’s surface. Whilelasers are also used to write information on the medium,it is actually theirheating properties which serve to encode data, ratherthan their opticalproperties. The latter are employed in the detection of the encoded data. Opticaldetection of data involves the recognition of “light transmittedor reflected (or, inprinciple, emitted) by the storage elements”,and its “translat[ion] into a formwhich the computer can understand, which in practice meansinto an electricalsignal.”2 Light is recognized by photoelectricdetectors which respond eitherIA. Bradley, Optical Storage for Computers:Technology and Applications,(Chichester, UK: Ellis Horwood Ltd.,1989),p.13.2Ibid,p.14.14directly to the intensity of lightor indirectly to the polarization of light. For themost part, the reflectivity of signalelements recorded onto the medium is used toachieve data recognition, although the direction of polarizationof the reflectedlight is also used in the detection of data storedon magneto-optical disks.The fundamental elements which distinguish the types of opticalstorage media are the method by whichinformation is recorded onto the storagemedium, the medium itself and its performance characteristics.The four maintypes of optical storagemedia are WORMs, ROM (Read-Only Memory),Rewritable and Optical Tape. This studywill deal with the first and latter twoformats, because they are the most tosuitable to archival purposes, as they dealwith storing new data, rather than of published information as do CD-ROMs.WORMs, Rewritables and Optical Tape are used by publicand private agenciesto record their own information, rather than as a purelytool for informationusually generated by others and disseminated.An analogy may be madecomparing registers and volumes; both may be made ofpaper, but the register, ablank book, is used to enter new information, while thevolume, a book of foliosbound after having been written, is used as a reference tool,Therefore, onlyWORMs, Rewritables and Optical Tape will be addressedin this study.WORM TECHNOLOGYThe first WORM drive availablein the United States was theGigadisc 1000, introduced by AlcatelThompson in 1983. 1984 saw theintroduction of the Optimem 1000 and anOSI Laser Drive 1200 from OpticalStorage International, which later becameLaser Magnetic Storage International.These first commercially availableWORM drives have been superceded bysecond and third-generation systems.The number ofWORM systems availablecommercially has15increased steadily since the mid-1980s. More than adozen companies currentlymanufacture WORM systems, including Eastman Kodak, Hitachi, LaserMagnetic Storage International, Matsushita (Panasonic), Mitsubishi, Pioneer,Ricoh (Maxtor Corporation), Sony and Toshiba. Optimem, a pioneer in thefield,ceased operations in 1991, and Optotech, one ofthe first to produce acommercially applicable 5.25” optical disk system, discontinued its WORMproduction in 1988. Optotech’s WORM product line was obtained by Shugart,but it has never been actively marketed by the new company.3 Japanesecompanies tend to introduce their products to their home markets before makingany export arrangements for North American or European markets. Thus, at anygiven time there are more products available on the Japanese market than thereare in the North American or European marketplaces. In most cases, there is alapse ofat least one year between the announcement of a new product and itscommercial availability. On occasion, new product lines are announced, but theynever actually appear on the marketplace.Most WORMS available commercially use tellurium-based ablativerecording technology, with dye-polymer based media as the second most popularform. The primacy of ablative recording technology may change in the nearfuture as dye- polymer media are less expensive to producethan tellurium thinfilm based media. Dual alloy and thermal bubble media remain single vendortechnologies. Most optical disk manufacturers sellblank media, although themedium itself may be manufactured by someone else. For example, Maxell, aHitachi subsidiary, produces the recording media for Hitachi’s WORM drives,and Ricoh, Maxtor Corporation’s parentcompany, produces the recording mediafor its subsidiary. Other manufacturers will designate an alternate sourcefor3W. Safl’ady, Optical Storage Technology1992: A State of the Art Review,(Westport, CT: Meckler, 1992),p.17.16recording material. For example, Plasmon manufactures the disks for Panasonicdrives, while Du Pont and Philips produce WORM disks for Laser MagneticStorage International and Eastman Kodak. This type of production distributionis done to promote competitiveness and to conform to American govermnentstandards for alternate procurement sources.4WORM systems present an efficient, accessible and archivaflyappropriate form for storing vast amounts of information. As their namesuggests, they use lasers to encode information permanently onto an optical disk.Once data are written onto a WORM disk, they cannot be altered or deleted,making of it the ideal medium for permanent archival storage of information.WORM disks are about twice as thick as the conventional CD-ROM disks andconsist of a “layer of recording material sandwiched between two plasticplates.”5 In most cases, the recording layer is either a tellurium alloy or a dye-polymer that has been deposited on a surface by a vapour plating process. Othertransparent layers of plastic are placed on this surface to protect the recordingsurface. The entire disk itself is enclosed in a hard case protected by a “slidingmetal shutter”.6 WORM disks can be double sided, but in order to either read orrecord on the disk’s reverse side, it must be taken out of the drive and flippedover. WORM capacity ranges from 600 megabytes on some 5.25 inch disks tomore than 10 gigabytes on a 14 inch disk. Numerous WORMs can be corralledin jukeboxes to create a truly massive information storage centre.74ibid,p.18.5S. Apiki and H. Eglowstein, “The Optical Option.”, 14:10, (October1989),p.168.6Apiki and Eglowstein, “The Optical Option”, p. 168;A. Elshami, CD-ROMTechnology for Information Managers. (Chicago:American LibraryAssociation, 1990),p.58.7Digital Equipment Corporation is currently marketingits RV64, whichconnects 64 two gigabyte WORM discs in a jukeboxfor a total capacity of 128gigabytes per system. It is accessed by 4 opticalplayers and was available for17The oldest and most common method ofWORM recording isablative pit technology. A high-poweredlaser either melts or vapourises thefocus spot to create a hole in the medium. This produces apermanent pit in themetallic recording surface underneath. A pit is formedwhen “surface tensiondraws the melted metal aside so that it solidifies with a crater-like rim aroundthehole.” Bubbles are formed when “the active layer[s] [are] vapourised by the heatof the laser beam but [are] contained by a plastic layer above”them.8Occasionally, the bubbles are intentionally burst open toform pits similar to thosecreated by purely ablative technology. There is a problemwith the vapourisationmethod, however, as it tends to allow the vapourised metal to be depositedonother parts of the disk, thus interfering with the writing and readingofthe dataon those parts of the disk. Fortunately, this problem can be eliminated byplacinga protective plastic layer above the blastlayer to contain the blast and preventdebris from affecting other parts ofthe disk.The blast then forms either a pit ora bubble on the surface of the recordinglayer. The actual data bits ofinformation are established by the presence or absence of these pitsor bubbles.These holes also expose the layer underneath the recordingmaterial, thus creating a change of reflectivity between the pits andthe unburnedsurface layer. The pit- burning/bubbling laser reads the data bitsby shining a lowpower beam on the recording surface, using a photosensor to detectany changesin reflectivity.9The data bits are thentranslated via the head assembly intoreadable information by the WORM drive’s computer system.The most common material used for the recording layer inablative$US 205,652. (DigitalEquipment Introduces Improved Data Storage System”,Aviation Week and Space Technology, 13 March 1989, p.61.)8Bradley, Optical Storage for Computers, p. 23-24.9Apiki and Eglowstein, “The Optical Option”, p. 168. ;Elshami, CD-ROMTechnology, p. 21.18recording is tellurium thin film, as it “offers good thermal sensitivity for low-power recording, high signal-to-noise ration, limited thermal conductivity toprevent undesirable increases in pit sizes, good resolution for high densityrecording, and good media stability.”10Tellurium thin film disks have anexpected shelf stability, that is, the amount of time a disk can be storedunrecorded before recording accuracy is affected, of five years. They also have astorage stability, that is, the length of time one could expect to retrieve data withreasonable accuracy, often to forty years.The bubble, or thermal-bubble technology, mentioned above wasone of the first to hit the market, but is far from the dominant WORM variantavailable now. Currently, only one company, ATG Gigadisc, uses thistechnology for its product line. This form of recording technology was “brieflysupported by the Optimem 1000, a first-generation WORM drive which couldalso be configured for ablative recording of tellurium thin films.” ATGGigadisc claims its newest product line has a shelf stability of five years and astorage stability of thirty years. Its first- generation disks had a storage stabilityoften years.Dye-based optical recording is a popular and less expensivemethod of writing information to WORMs. It is also known as dye-polymer,dye-in-polymer (DIP) and organic dye binder media. Dye-polymer disks also usepit-burning technology, except that the medium facilitates sharper pit edges andthus sharper and clearer changes in reflectivity. Alternatively, information can berecorded by a laser which operates “at the dye’s absorption wavelength” tobubble or deform the recording layer. The laser-readable changes in reflectivityin this recording technique occur betweenthe “diffused and pure dye areas” of10Saffady, Optical Storage Technology 1992, p.5.11Ibid, p. 8.19the disk.’2 Bubbling or deforming allows the ablated material to fall around therim of the pit rather than into the centre, as can happen with ablative pittechnology. This allows the read laser to read the data bits much more clearly,thus reducing the number of errors written onto the disk. The 14” disksproduced using this method have three times the capacity of the previous 12”disks.’3This method of recording information is used by Eastman Kodak,Pioneer and Ricoh, the latter ofwhich sells its WORMs through Maxtor in theUnited States. Dye-polymer disks have an expected shelf stability of five yearsand a storage stability of fifteen years. Dye-polymer advocates claim this mediumhas “higher read/write speed[s], lower threshold energy requirements for pitformation, greater stability, and lower production costs” when compared tooptical recording systems which utilize tellurium thin films.14Another method of recording information on WORMs is by phasechange technology. The disks used in this process are similar in construction tothe tellurium thin film disks used in ablative recording. The disks are constructedof “tellurium and/or selenium compounds which are typically alloyed with smallquantities of other15Phase change differs from other recordingmethods in that the recording method does not change the shape ofthe surface ofthe recording medium. Instead ofburning a pit in the disk, the drive laser altersthe structure ofthe recording medium so that it changes the phase of reflectedlight.At room temperature, certain tellurium alloys can exist in either12Ibid, p. 6.13P. M. Artlip, “Different Optical Disk Formats Co- Exist to Provide End-UserApplications Flexibility”, IMC Journal, 24 (March/April 1988),p.15.14Saffady, Optical Storage Technology 1992,p.7.15Ibid,p.8.20their crystalline or amorphous state, and are capable of being switched back andforth between either state. A low powered laser creates the shift to a crystallinestate, while a higher powered laser causes theshift back to the amorphousstate.’6 The optical reflectivity is differentfor each state, and is read in the samemanner as the pits created by ablative pit technology, as the drive “detects phasechanges in light from the read laser reflected off the disk surface.”17Phase-change disks use the same reading technique as other WORM and CD-ROMsystems, and are the only type of recording technique that can be used in bothWORM and rewritable formats. Both forms ofphase-change media use the sametechnology, except that when the disk is a WORM the phase- change isaccomplished rapidly, thus making the transition irreversible.Eastman Kodak and Matsushita produce phase change WORMsand their drives, the latter of which are sold in the United States by Panasonic (aMatsushita subsidiary) and by Plasmon Data Systems. Plasmon, however, uses aplatinum recording layer rather than the traditional tellurium thin film. Phase-change disks have the usual shelf stability, and a storage stability of fifteen to fiftyyears, as claimed by Matsushita and Plasmon respectively.18A variant of phase-change recording methods is “moth- eye” ortexture change. The recording substrate is imprinted with a relief pattern that issmaller than the spots used for denoting bits of information. This substrate isthen covered with a very thin layer ofplatinum. The platinum layer repeats therelief pattern, thus scattering light and lowering the reflectivity of the layer. To16C. Dollar, Archival Theory andInformation Technologies: The Impact ofInformation Technologies on Archival Principles and Methods, Informatics andDocumentation Series 1. (Macerata, Italy: University ofMacerata, 1992),p.31.;T. Hendley, CD-ROM and Optical Publishing Systems, Cimtech Publication26, (Hatfield, Herts, U.K.: CimtechIBNBRF, 1987), p. 31.17Apiki and Eglowstein, “The Optical Option”,p.168.18Saffady, Optical Storage Technology 1992, p.8.21record a bit of information, the laser melts a spot on the surface ofthe substrate,creating a smooth area on the metal layer, and thus a change in reflectivity ofthespot in question.’9The read laser reads this change in reflectivity in the sameway as those with information written by other recording techniques. The term“moth eye” comes from the impression that the relief pattern and its reflectivityresemble those of a moth’s eye. “Moth eye” is not a common method ofrecording information on optical disks.Dual alloy or bimetallic alloy medium is a variation of phase-change technology, except that data are recorded by fi.ising three alloy layers,creating a difference in the level of reflectivity between the fi.ised and the non-fused areas. The medium consists of two metal alloys, often tellurium andbismuth, and selenium and antimony, in thin film form coating a polycarbonatesubstrate. The layers form a sandwich, with two layers of selenium and antimonysurrounding a layer of tellurium and bismuth. All the layers are covered by aprotective seal, thus the name “direct seal” is often used for this type of medium.To record information, the recording laser fuses the three layers, forming a four-element alloy spot which possesses a reflectivity distinctly different from theunused areas surrounding it. Generally speaking, the fused parts equal a 1 bit,the unfused parts a 0 bit.2°Currently, Sony is the only manufacturer using this technology,and only for the manufacture ofWORMs. The shelf stability ofthis medium isanalogous to the other recording methods, but its storage stability is estimated tobe much higher. Sony claims its “Century Media” have a playback life of 100years. While these disks may have direct applications for those users who requirelong-term storage of information, the question ofwhether the information on the19Bradley, Optical Storage for Computers, p. 24.20Saffady, Optical Storage Technology 1992,p.7.22disks will be accessible by future hardware and software must also be taken intoconsideration when analysing the potential and/or validity of such claims.Although the methods of recording information may differ fromWORM to WORM, the signal elements are still arranged serially on each form ofdisk. All signal elements are arranged on a track in either concentric circles, ormore commonly, as a spiral reaching from the inside to the outside of the disk.These track(s) can be either spaced equally apart, or arranged in bands similar tothose used on phonograph records. Data are divided into sectors along eachtrack. Each sector has an identi1,’ing header similar to those used on magneticdisks. Most WORMs are preformatted with this sector identificationinformation.Writing information to a disk, however, requires that even moremethods of control for accuracy and ease of retrieval be maintained.Consequently, controls have to be maintained over both the spaces between thewritten bits and the radial position of their tracks. Control ofthe radial positionis particularly important as it is “impossible to make the axis ofthe rotationexactly concentric with the header pattern, and the error is usually much greaterthan the track spacing.”21 Radial position control is often achieved through theuse of a “pre-groove” which is an extension of the preformatting process andproduces a track which is narrower than the laser spots written to the disk. Thewriting laser either follows the groove and writes the bits on the groove, orwrites on the areas between the grooves. These grooves are also used as “clocksignals” to indicate spacing between elements, and aid the writing and reading ofthe signal elements.22Preformatting also determines the track layout and thus the way21Bradley, Optical Storage for Computers, p. 25.22Ibid, p. 25.23information written to the disk is arranged on the disk. Track layout isdetermined by disk rotation and is achieved in two ways: Constant AngularVelocity (CAV) or Constant Linear Velocity (CLV). CAV indicates that the diskrotates at a constant speed, and thus the information is written to the disk at aconstant rate. Consequently, the spacing ofthe bits is increased as the track getscloser to the edge of the disk. This results in a greater recording density near thecentre of the disk, which decreases as the track progresses towards the outeredge. The disparity in recording density can also necessitate changes in theenergy used to write the information on the disks, because the written bits on theouter track are in laser range for a shorter time than those on the inner tracks. Asa result, the writing power may have to be adjusted to compensate for this timedifferential ifthere is not a “sufficiently wide tolerance on the amount of energyused to change a signal element”.23 CAV written disks have a lower capacitythan those written using CLV, but information can be written to the disksomewhat faster. There is a modified form of CAV, MCAV which maintains aconstant disk speed, but varies the reading and writing rates to correspond withthe track radius, thus maintaining a maximum writing capacity similar to thatachieved with CLV.CLV differs from CAV in that the disk rotates at a various speeds,depending on the radius of the track being written to. The difference in diskrotation speed keeps the spaces between written bits the same on each trackregardless of whether its track is in the centre or at the edge of the disk. Thisprocess allows all tracks to be written to the maximum density the medium willpermit, “typically increas[ing] the capacity of a disk by50%.”24These changes inspeed, however, add to both the complexity ofthe system, as an additional servo23Thid,p.26.24Thid,p.26.24system is needed to control the disk rotation speed, and the access time neededto retrieve the information. There is also a modified form of CLV, namedMCLV, which divides the disk into bands, maintaining a uniform speed withineach band, rather than with each track. This process does not achieve the fullwriting capacity of CLV, but it still achieves a greater rate than CAy.CAV is the most common system oftrack layout in use forWORMs, but all of the above formats are used in commercially available systems.WORM drives are available, however, which are capable of operating in bothCAV and CLV. Nonetheless, while WORMs vary in their method oftracklayout, Compact Audio and CD-ROMs use CLV exclusively.Error detection is also a significant element of optical disk storagetechnology. It is vital to have such controls, as no storage system is perfect, yetperfection, or near it, is a requirement of any user of information storage systems.Undetected errors in the data stored on a user’s optical disk can have very seriousrepercussions for the user, and thus powerful error detection codes have becomea standard feature of optical storage systems. However, it is not economically ortechnologically practical to eliminate all errors. Therefore, a system can onlyhope to be able to minimize the errors to a level acceptable by those who willeventually read and use the stored data. The standard error rate for nonrecoverable errors is not more than one in1012bits read and, for undetectederrors, not more than one in1014bits read. These error rates are roughly theequivalent to one uncorrected error a year, or one undetected error in 100years.25Error detection and correction are achieved by redundancy in thecoding of data. Errors are detected by the redundant coding of data, and by tests25Ibid, p. 33.25which detect substandard coding such as low signal amplitude. Correction iscarried out by either on-the-fly or retry methods. The former involves thecorrection ofthe data within the drive before it is transferred to the host, whilethe latter simply involves the repetition ofthe data transfer. Powerftul errorcorrection codes are the norm for optical disks, and, as a result, disks can have adata redundancy of2O5O%.26Checking for errors can be achieved in two ways: either bychecking the data on the revolution after it has been written, or by reading eachbit soon after writing. The former is the more common process, and is similar tothe methods used with magnetic disks. In this process, an entire sector or awhole track is checked for accuracy on the next pass of the write laser. Thecopied data are not compared to the original data, but the error correction codesare used to test the accuracy of the written bits. The latter method is the use ofeither the Direct Read After Write (DRAW) or Direct Read During Write(DRDW) methods. DRAW is an optical storage method used on WORMs torecord information locally or on-site. During this procedure, the recordingmachine reads data after they are written to the disk, continuously comparingthem with the incoming data stream. If an error is detected, the correctinformation is immediately rewritten to another part ofthe disk, as informationon WORMs cannot be altered or erased, only augmented. DRDW systems checkeach bit “against the bit which should have been written at that location.”27DRDW is more complex and slower than DRAW, but still faster than reading thedata on a second revolution. Once errors are discovered, if they are beyond theparameters set out by the system’s error correction codes, the correct data arethen rewritten to the next available free sector of the disk or to a special section26Thid,p.35.27Thid,p.35.26set aside for rewritten data.Regardless of the variations in recording technology or base media,WORM disks are typically encased in a plastic cartridge to make handling easierand to limit physical and environmental damage to the disks themselves.Although the size of the cartridges may differ from system to system, at thepresent time the actual WORMs only come in three sizes: 5.25”, 12” and 14”.The Japanese market supported 8” disks for a brieftime in the 1980s, but thesewere not very commonly used in North America.Fourteen inch WORMs are currently manufactured by only onecompany, Eastman Kodak. As a result, Kodak is the creator ofthe de factostandard for this particular size ofWORM disk and its accompanying drivesystems. Its WORM cartridge is the “basis for the ISO CD 10085 standard forfourteen-inch [WORM] cartridges developed by the International StandardizationOrganization (ISO).”28 The Kodak Model 6800 optical disk drive introduced in1986 is named for the recording capacity ofthe original disk-- 6,800 megabytesor 6.8 gigabytes per double-sided disk. By 1989, storage capacity for the Model6800 had been upgraded to 8.2 gigabytes, although this model did not becomecommercially available. In 1991, the double-sided disk capacity was increased to10.2 gigabytes. The original system used dye-polymer recording media, but thiswas changed to phase-change technology for the 1991 version. Kodak offersupgrades for the older 6800s, allowing them to read and record on both 6.8gigabyte and 10.2 gigabyte versions.29The first commercially successfbl WORM systems were those withtwelve-inch drives and media. Introduced to the commercial market in the mid1 980s, the recording capacity of 12” disk systems have risen steadily ever since.28Saffady, Optical Storage Technology 1992,p.20.29Ibid, p. 20-21.27The first generation of 12” WORMs had a recording capacity of two to fourgigabytes of data per double-sided disk. By the late 1980s, however, second andthird generation 12” systems offered recording capacities of 2.4 gigabytes to 6.4gigabytes. WORM recording capacity had been expanded even further by theearly 1 990s, with the introduction of ATG’s Gigadisc 9001. The Gigadisc 9001has a 9 gigabyte recording capacity and is the “capacity leader among twelve-inchdrives.”30 These increases in 12” WORM system recording capacities pushedKodak’s 14” WORM system to increase its recording capacity in order tomaintain the competitive edge and market niche of their 14” product.While 12” WORM systems may be commonly used, they are theleast standardized. The recording technologies used for 12” WORM systems arethermal bubble, ablative and dual alloy. At the present time, all 12” WORMsystems are proprietary, and there are no standards for the production ofWORMsystems or cartridges. There is an ANSI committee working on producingstandards for 12” WORMs, but it is not expected to produce anything concretebefore the mid-1990s.The first 5.25” WORM system, the ISi 525WC, was introduced in1985 by Information Storage Incorporated (ISi) with a single-sided recordingcapacity of 115 megabytes. By the late 1 980s, dye-polymer and phase-changetechnologies were being used, and the double-sided recording capacities hadincreased to between 600 megabytes to 1.28 gigabytes.31Prior to 1987-88, all 5.25” WORM products used proprietaryrecording media. In 1987 and 1988, a number of leading 5.25” WORMmanufacturers launched products which used media that conformed to theISO/IEC 9171 standards for 5.25” WORM cartridges. These standards specified30thid,p.24.31Ibid, p. 24.28the “magnetic clamp method, hub diameter, central hole diameter, trackingmethod, and other characteristics of optical disk cartridges.”32 Althoughadherence to the above mentioned standardwould lead one to believe allcompliant 5.25” WORMs were the same, the ISO/IEC standard supports tworecording formats: Format A or composite servo (CCS) and Format B orsampled servo (SS). The two formats use different methods of “handling thecontrol of servo signals which permit accurate tracking and focus of a drive’soptical head during recording and playback.” Format A achieves this tracking andfocus via a grooved media, while Format B employs a succession of marks oneach side of the centre of a track. Both formats may be compliant with theISO/JEC standards, but they are incompatible with each other and thus requiretheir own, non-interchangeable media.33The basic configuration of WORM systems usually consists of anumber of interdependent parts. To begin with, documents entering a WORMsystem must be in digitized form. Transferring non-digital documents to digitalformat can be achieved by scanning the original with document scanners, usingeither small hand-held models or larger ones which resemble photocopiers. Adocument conversion scanner system is comprised of four parts: “the generationofthe digital image representation”, compilation of the index data, allocation ofthe storage address and storage of the imageon the disk.34 Documentsunsuitable for scanning can be transferred into digital format via a video recorder.The taped analogue material can then be transferred from non-digital to digitalform. This method is particularly effectivefor photographs, slides and negatives,32Ibid, p. 25. The manufacturers who have accepted this standard areFujitsu,Hitachi, Laser Magnetic Storage International,Mitsubishi and Pioneer.33Ibid, p. 25.34G. Walter, “An Overview: Technologyand Application Status of OpticalDisk Systems”, IMC Journal, 24 (July/August1988),p.10.29as they can be relatively easily placed on videotape, and then later transferred to aWORM disk.35WORM systems also must have a control microcomputer tocoordinate all the peripherals and the software programs which run the system.Peripherals include: a laser printer for creating hard copies ofthe stored images; ahigh resolution monitor for viewing the documents and text; and possibly LocalArea Networks (LANs) for multiple use ofthe system and communication withoutside interests. Traditional magnetic disk drives are also needed for storage ofthe database indexes, and database application, information retrieval and systemsoftware.36 Most importantly, knowledgeable people are needed to operate andadminister WORM systems for the systems to work effectively and efficiently.While WORMs require little in terms of special storage orconservation considerations, they can, like anything else, be subject to damage.Disk integrity can be affected by the swelling, shrinking, bubbling or blistering ofthe pits, causing changes in reflectivity and eventual degradation of data.Oxidation ofthe reflective layer can also cause a similar deterioration ofdata.37Consequently, more time and testing is needed to determine the long-termstability ofWORM disks for archival storage purposes.As a relatively new technology, however, WORM systems areunproven in terms of their lasting ability. There are some estimates ofthe lifespan of the disks, but their ability to maintain archival quality records forextended periods of time has yet to be proven. Generally speaking, the life35L. Howe, “The Use of Optical Disc for Archival Image Storage”, Archivesand Manuscripts, 18 (May 1990),p.100-101.36B. Cinnamon, “Optical Disk Applications”, IMC Journal, 24 (July/August1988),p.20.37A. Calmes, “To Archive and Preserve: A Media Primer”, Inform, (May1987),p.17.30expectancy ofWORM disks is between 10 to 100 years, depending on the sourcecited. Realistically, the current WORM life expectancy is in the range of 20 to 30years, which is comparable to some electronic media, but still short of the 100year life expectancy of microfilm. There have been, however, accelerated testsperformed which claim that “no visual impairment occur[ed] after 100 successivecopy generations of single video images.”38Despite these findings, the accuracyof accelerated tests to predict WORM life expectancy is still in question, as it isunclear whether disk performance under normal use conditions can even beduplicated by such tests. Unfortunately, only time will tell whether WORMs willbe able to live up to their accelerated test results and their commercialexpectations.REWRITABLE TECHNOLOGYRewritable optical disk technology has been the ultimate goal ofthe optical disk industry since its inception in the early I 970s. This goal wasrealized in 1988, with the introduction ofMagneto-Optical (MO) disk systems tothe North American market.39 Panasonic introduced the first phase-changebased rewritable disk drive in 1990.The most common form of rewritable optical disk technology isMagneto-Optical (MO), also known as Thermal Magneto-Optical (TMO). Thisis a hybrid technology, because it stores information magnetically, as do magneticmedia, but uses a laser to read and write the information to the disk. Magnetoopticals and WORMs use the same basic reading techniques, but MO disks use38Howe, “The Use of Optical Disc”,p.100.;Howe cites as his source for thisinformation: Library of Congress, LC Information Bulletin, 47(14), (WashingtonD.C.: Library of Congress, 1989),p.124.39Saffady, Optical Storage Technology 1992,p.27. Rewritable optical diskdrives were introduced in Japan in 1987.31the same principles as magnetic disks for recording purposes. MO disks areessentially “multilayered magnetic disks which employ vertical recordingtechniques instead ofthe horizontal-- sometimes described as longitudinal--recording methodologies associated with conventional magnetic media.”4°Vertical recording techniques align the magnetic domains perpendicular to thedisk’s surface, while horizontal techniques arrange the domains parallel to thedisk’s surface. Horizontal recording allows for the domains to be placed muchcloser together, thus achieving a higher recording density than those arranged inparallel. Horizontal recording is also used by high-density floppy disk systems,particularly those which employ barium- ferrite media. MO disks are essentially“optically assisted magnetic media”, which have the same benefits as WORMsystems, their enormous storage capacity, the same stability of data andportability of medium, as well as the added adaptability of magnetic media.4’MO disks work on the same principle as magnetic media: bits arecoded as either magnetically positive or negative. Initially, the magneticorientation of the MO disk is uniform with the magnetic north pole down. Thepolarity is changed by coercive force, which is low at high temperatures but theopposite at low temperatures. By laser-heating a spot, which represents one bitof information, to 150 degrees Celsius “the resistance ofthe spot to changes in itsmagnetic field drops to nearly zero, and the spot is changed to north pole up”.42Once this is achieved, the spot’s magnetic domain is reoriented by anelectromagnetic field. When the spot cools, its magnetic orientation is theopposite ofwhat it had been previously. The use of heat in the recording anddeletion process is where MO differs from purely magnetic media, as data40Ibid,p.10.41G. E. Kaebnick, “Rewriting the Future: Putting Rewritable Optical Disk onthe Market”, Inform 4 (May 1990),p.17.42Ibid,p.17.32recorded on the latter can be destroyed by the merepresence of a magnetic field,whereas data on a MO disk cannot be changed “even by a relatively strongmagnetic field unless heated”.43To read the information recorded on the MO disk, the read laserreads the information by sensing the changes in magnetism, not the changes inreflectivity as is the case with WORMs. Data are erased by a less powerful laserwhich heats the area in question and reverses its magnetization to its originalmagnetic north pole down orientation. This action returnsthe bits to their zerobit state. Data are rewritten to the erased areas only on a subsequentdiskrotation. At the present time, two passes are needed toerase and rewrite data toMO disks, but it is predicted that future developments will reduce this to onedirect- overwriting pass.A phenomenon known as the Kerr effect is responsible for theability to retrieve information stored on a MO disk. Under the Kerr effect, amagnetic surface affects the polarization of reflected light by rotating it ineither aclockwise or counterclockwise direction, depending on the orientation ofthemagnetic particles on the disk. These particles, representing bits of information,will be read by the laser and an optical pickupmechanism as either a one or azero, based on the way they detect the rotation of reflectedlight from themagnetic particles.44The medium used in MO disks is a multilayered medium comprisedof layers of thin films combined with iron, certain rare-earthsand transitionmetals. Rare-earths elements are common in the earth’scrust, but derive their43J. A. McCormick, A Guide to Optical StorageTechnology: Using CDROM. WORM. Erasable. Digital Paper. and OtherHigh-Density Opto-MagneticStorage Devices, (Homewood, IL: Dow Jones-Irwin,1990),p.77.Saffady, Optical Storage Technology 1992, p.11.;Bradley, Optical Storagefor Computers, p. 56.33name from the fact that they were found originally in rare minerals. They are theelements with the atomic numbers 21, 39, and 57-71. Terbidium, neodymium,dysprosium and gadolinium are examples of rare-earths elements used in MOrecording media. Transition-metals are elements which have characteristics ofboth metals and non-metals. They are the elements with atomic numbers 22-28,40-46 and 72-78. Examples used in MO technology include cobalt, platinum,titanium, chromium and zirconium. The most commonly used combination incommercially available products is terbium- ferrite-cobalt.45Regardless of the elements used in the medium, the recordingmaterials are all placed on the recording substrate in the same manner: eithervacuum deposited or sputtered onto glass or plastic substrates. Glass substratesoffer “superior uniformity, optical clarity, mechanical stability, scratch resistance,freedom from warpage and resistance to moisture absorption.”46 Plasticsubstrates are less expensive to produce and are lighter, thus facilitating fasterrotation times.There are, nonetheless, problems associated with MO recordingmedia. Oxidation ofthe rare-earths and transition-metals, for example, causesthe medium to age and deteriorate, resulting in an inability to retrieve theinformation stored on the disk. Terbium, in particular, oxidizes easilycontributing to a decline in magnetic coercivity, recording sensitivity, bit errorrates and playback stability. Multi-layer barrier coatings and oxidation-resistantalloys can, however, retard the aging process.4745Saffady, Optical Storage Technology 1992,p.12. Other possible MO mediainclude: ferrite-cobalt, ferrite terbium, ferrite-silicon, ferrite-terbium-gadoliniumand ferrite-terbium-indium. Iron-garnet media are touted by some to be themedia of the next generation ofMO disks.46Ibid,p.12.47Ibid,p.12.34The estimated lifetime for MO disks is considerably shorter thanthat touted for WORMs, and the periods of their shelf and storage stability areidentical. For a rewritable disk to be useful, it must be able to both record andretrieve the information stored on it for an equal length of time. Mostmanufacturers claim a shelf and storage stability often years for disks withplastic substrates. Laboratory examples, however, suggest potentially longerlifetimes for such disks, and even more so for those utilizing glass substrates. Forexample, poly-carbonate plastic substrate disks produced by the NECCorporation claim a life of fifteen years. Several other manufacturers, however,claim a life of 15-25 years for products using glass substrates.Phase-change technology is the other recording method used inrewritable optical disks systems. The rewritable version of phase-changetechnology did not hit the market until 1990, and it is only marketed byMatsushita. The basic concepts utilized in rewritable phase-change technologyare the same as those used in the WORM version, but in the rewritable versionthe transition between the amorphous and crystalline state ofthe recordingmedium is reversible. A laser heats a spot on the recording layer to just above itschange of state, and rapid cooling ofthe point in question transforms the areafrom its crystalline to its amorphous state. The medium is more stable in itscrystalline form, and thus tends to revert to it when it is heated to just below itsmelting point.48Like its WORM counterpart, the reversible form of phase-changetechnology also relies heavily on the use of tellurium thin films alloyed with someother element, such as selenium, gadolinium, indium, antimony, germanium, tinor titanium. Matsushita’s current product uses tellurium based media. Other48Ibid,p.13.35alloys are used, but these are currentlyonly at the laboratory experimental stage,and far from commercial applications.49Unlike MO technology systems, rewritable phase-changetechnology systems are able to supportdirect overwriting, as they do not need toreset their “spots” to a neutral statebefore they can be rewritten. This directoverwriting capability allows data to bewritten and erased in a single pass, ratherthan in the two passes MO disks need toperform the same function. This shouldgive phase- change rewritables the advantageof faster read/write rates, but iscounteracted by the slow amorphous-to- crystalline transitiontimes which arecurrently a characteristic of phase-changemedia.5°While this slow transitiontime condition may change in thefuture, phase- change rewritable optical diskscurrently have limited practicality in situationswhere quick writing and erasure ofinformation is a practical necessity.Like MO disks, phase-change rewritable disks havean expectedshelf and storage capacity of ten years, although there aresome experimentalaging tests which suggest a longer lifespanmay be possible. Phase-change mediaare, however, susceptible to “accidentalerasures” at low temperatures, acharacteristic not shared by their MO counterparts,which require both a hightemperature and a surrounding magnetic fieldfor data erasure to take place.Phase-change technology is also apparentlyless durable than MO and has a lowerread/write capability. The MO disks usedin the systems marketed by Sony andRicoh have the capability to read andrewrite data at least a million times beforedata degradation sets in. Matsushita’scomparable phase-change system only hasa read/write capabilityof approximately 100,000 times before the onset of data49Ibid,p.13. Experimental alloys include:indium- selenium-lead, indiumselenium-thallium, indium-selenium-cobalt, indium-selenium-antimony, galliumantimonide-indium antimonide, silver-zinc,gold-germanium.50Thid,p.13.36degradation.5’On the other hand, phase-change recording materialsare largelyunaffected by ambient temperatures and relative humidityencountered in mostoffice environments, and are completely unaffected bymagnetic fields.52A third form of rewritable optical disk system is based on dye-polymer recording technology. Dye-polymer rewritables were developed by asmall American company, the late Optical Data Incorporated (ODI), in thelate1980s, but have yet to become available commercially. Nonetheless, this formofrewritable optical disk system is one to watch for in thefuture as it purports to beread compatible with most CD-ROM systems. Thiscapability would allow datato be written to a dye-polymer rewritable diskat one location, then be usedsomewhere else like with a regular CD-ROM disk. Suchdisks would have theadvantages of both rewritability and a wider read capability.53 This capacity alsofacilitates the creation of multifunction drives, a move which would make the useof optical disk technology simpler, more functional and more widely applicable.Dye-polymer WORMs and rewritables both use dyed layers ofplastic as their recording layers, but rewritables use two layers “made up ofdifferent materials sensitive to different frequencies oflight” rather than one dye-polymer recording layer.54 Information is written to the disk by shining thewritelaser through the top, or retention layer, through to the bottom or expansionlayer, causing a bump to form in the polymer. The retention and expansion layersare colour sensitive, and only the write laser has the rightfrequency to shinethrough and write to the expansion layer. Thebump created by this processrepresents a data bit. To erase information, adifferent laser on a different51McCormick, A Guide to Optical Storage, p. 80.;Bradley, Optical Storagefor Computers,p.58.52Saffady, Optical Storage Technology 1992,p.14.53McCormick, A Guide to Optical Storage Technology, p.81.54Ibid,p.81.37frequency heats the retention layer immediately above the bump, smoothing outthe bump and returning the recording layer to its original state.55Rewritable dye-polymer media can be used with most ofthecurrent rigid and flexible substrates, and can be manufactured by a “thick-film,solvent-coating process that is similar to the well-established manufacturingtechniques associated with magnetic media.”56 As with WORMs, dye-polymerrewritables should be easier and less expensive to manufacture as they do notrequire either vacuum deposition or thin film sputtering as do other forms ofoptical disk media. Dye-polymer rewritables should also be less susceptible tooxidation than other rewritables as they are composed of inert materials ratherthan the oxidation-susceptible metallic thin films.57Thus far, however, only laboratory examples of dye- polymerrewritable technology have been unveiled. Prototype 3.5” and 5.25” dye-polymerrewritables with a single-sided storage capacity of 100 to 500 Mb were presentedby ODI in the late 1 980s, but commercial forms were never introduced. In 1988,Tandy Corporation announced it would be using ODI’s media in their High-Intensity Optical Recorder (THOR). THOR, however, never made it to theconsumer stage, and while other companies have flirted with the idea ofusingdye-based rewritable media, none have introduced any such consumer products.Prior to its dissolution in 1990, ODI signed over non- exclusive licensing rightsto Du Pont Optical (PDO) and Teijin Limited, but none have produced anycommercial rewritable systems as ofyet. At this point in time, the immediatefi.iture of dye-polymer based rewritable optical disk systems is questionable.Rewritable optical disks are very similar to WORMs in terms of55Ibid,p.81; Saffady, Optical Storage Technology 1992, p. 14.;Bradley,Optical Storage for Computers,p.56.SbSaffady, Optical Storage Technology 1992, p. 14.S7Ibid,p.14.38their physical recording organization. Both WORMs and rewritables use similarpreformatting, pregrooving and clock signals, and both types of optical storagemedia can use either CAV or CLV to record information to their respectivedisks. A proprietary non-standard 5.25” MO system manufactured by Maxoptix,however, supports a modified zoned constant angular velocity (ZCAV). Unlikeregular CAV disks, ZCAV disks have more sectors and data on their longer outertracks, rather than their shorter inner tracks.58Error detection is also managed the same way it is on WORMs.Errors are detected on-the-fly, and to the same rates that are specified forWORM disks. At this time, rewritable systems can only detect write errors onthe next revolution, as rewritable systems using DRDW are not yet availablecommercially.Rewritable media come in two sizes: 5.25” and 3.5”. Both sizesare intended to be used primarily as additions to desktop installations, unlike thelarger WORMs. These sizes also conform nicely to the multifunctioning systemconcept which incorporates both WORM and rewritable drives within the sameoperating system.The 5.25” rewritables are, like their WORM counterparts, encasedin a rigid plastic cartridge. The capacity of these double-sided disks ranges from512 Mb to 1 Gb, and most manufacturers of these sized disks havetheir productconform to the ISO 10089 standard for optical disk cartridges.59 Thosemanufacturers which employ MO disks in their multifunctioning systems also58Ibid,p.29-30. In 1990, ZCAV was endorsed by a number of manufacturers,hoping to encourage an ISO standard based on the ZCAV format. Themanufacturers included Maxoptix, Hewlett-Packard,Philips and Du PontOptical, Optical Storage Corporation, and Mitsubishi.59Ibid,p.29. Manufacturers which comply to this standard includeSony,Ricoh, Hitachi, Sharp, Hewlett- Packard and Panasonic.39comply to this ISO standard. The ISO standard uses the CCS format exclusively,unlike the comparable WORM standard which encompasses both CCS and SSrecording formats. Phase- change media of this size are proprietary, withPanasonic’s product offering a 1 Gb capacity per double-sided cartridge.Although the 3.5” rewritables existed in laboratory form as early as1985, it took until 1990 for them to become commercially available. The only3.5” rewritables currently available employ MO recording technology, andphysically look much like their floppy disk counterparts, except they aresomewhat thicker. These drives are currently being manufactured by thefollowing companies: Sony, IBM, and Mass Optical Storage Technologies(MOST), a subsidiary ofNakamichi Peripherals Corporation. A significantnumber of other manufacturers have expressed interest in these sized drives,indicating a larger market share for these drives in the future. The 3.5”rewritable optical disks may become the floppy disks of the fi.iture.The 3.5” rewritable optical disk systems are unique in one respect;they are the first optical storage systems to post-date the ISO standards for theinterchangeability of optical disk cartridges. Consequently, all 3.5” disksconform to the ISO 10090 standard, “which specifies a nominal recordingcapacity of 130 [Mb] per single-sided magneto-optical disk cartridge.”60 All butone manufacturer of 3.5” systems uses disks that conform to this standard. In1991, MOST introduced a proprietary system which supports a 256 Mbcartridge. MOST drives also support the ISO standard cartridges; two separatecartridges are needed for each recording mode. All current 3.5” rewritablesystems use the CCS recording format, but the ISO standard supports the use ofa Discrete Block Format (DBF),which is similar to the SS recording format used60Ibid,p.34.40by some WORMs.6’As a whole, rewritable optical disk drives have faster access timesthan their WORM counterparts, but are still slower than similar magnetic diskdrives. The average access time of a 5.25” rewritable drive is between 60-70milliseconds, a time which is close to the access times of the slowest magneticdisk drives. The access times of the 3.5” rewritable drives is in the 50-70millisecond range, but access times are expected to improve for both therewritable and WORM based systems.62OPTICAL TAPEA third form of optical storage system is optical tape.63 Opticaltape systems have been in the experimental stages since thelate 1970s, but havenot progressed to the commercial stage as quickly as have other forms of opticalstorage systems. ICI ImageData, a British company, developed its “digitalpaper” product in the mid 1980s, but commercial application of the medium didnot occur until 1989. Digital paper is a form of optical storage similar toWORMs, yet is more flexible and versatile in both its physical and Ilinctionalabilities. As with WORMs, information recorded on digital paper is non-erasable, but digital paper can be cut into strips, disks, tapesor tags. The name“digital paper” is in itself misleading, as this is not a paper-based medium, but isconstructed of a “dye polymer infra-red sensitivecoating on a polyester-basedsubstrate, capable of being recorded on by laser”, and has a projectedlife span of61Ibid, p. 34.62The average access time for 5.25” WORM drives is between 75-250milliseconds, 12” drives 90-500 milliseconds, and700 milliseconds for 14”WORMs.63Optical tape is also known by its brand name, DigitalPaper. In the interestofvariety, and as this system is proprietary,the two terms will be usedinterchangeably in this study.4130years.Digital paper consists of a four-layer sandwich of substrate,reflective metal, active and protective layers. The substrate layer is made of a 25-27 micron deep polyester-based film (Mellinex), which provides the mechanicalstrength of the entire structure. The next layer is a thin coating of metal, similarto silver plastic balloon foil. This layer forms a passive mirror which is notaffected by the recording process. The active layer is a transparent polymermade up of an infrared absorbing dye. Information is recorded by beaming aninfrared laser at this layer. The dye absorbs the radiation emitted by the laser andconverts it to heat energy, causing the polymer to form pits. This layer is a verypoor conductor, thus allowing the laser’s heat to be more concentrated to createsharper and smaller pits. As a result, the pits, and thus the data bits, can bepacked more densely onto this particular medium than on a traditional WORMdisk. A full tape, which measures 880m by 35mm and fits onto a 12 inch reel,holds a terabyte of data. The fourth layer is a transparent protective polymer.Commercial versions may also have a fifth polymer layer to protect and facilitatethe smooth movement of digital paper lengths when used in reels andcassettes.65As in other WORM systems, in order to read data, the pit-burninglaser is beamed back at a lower intensity onto the recording layer. The laser thenreads the changes in reflectivity caused by the pits in the recording layer. Digitalpaper disks, exploit what is termed the “Bernoulli effect”, and thus must use aslightly different hardware system than traditional WORM disks or digital tape.64“Digital Paper is Write-On”, Canadian Data Systems, 20:6 (June 1988),p.67. This is a conservative estimate, and ICI Imagedata predicts a lifespan similarto that of Sony’s “Century Media”. For more information onthe lifespan ofOptical Tape, see Chapter two.6D. Pountain, “Digital Paper”, 14:2 (February 1989), p. 276.42The “Bernoulli effect” employs two digital paper disks whichrotate back to backclose to the underside of a fixed plate containing the recordingheads. Thespinning ofthe disks creates airflow currents that lift thedisks toward theread/write heads without touching them. The disksare held at a constant 50microns away from the heads, allowing the laser to keep a steadyfocus on thereflective layer. The disks cannot crash like hard disks, ashardware failuretriggers airflow depressurization, causing thedisks to fall away from theread/write heads, rather than into them.66The only company currently marketing optical tape drive systemsis a Vancouver-based company, CREO. The CREO system drive looks like alarge magnetic tape drive, but has the capacity to store oneterabyte ofinformation on a tape 880m long and 35mm wide. Each tape has sets of 33tracks, including a clock track, and information is recorded in parallel sequencesalong the track. While parallel, however, the actual placement ofthe tracks isacross the tape rather than parallel with the edge, and uses oscillating head toread the data from the tape. This format allows for more data to be written tothetape and faster retrieval times. Once a setof 33 tracks has been written acrossthe tape, the tape is skipped forward tothe next unwritten part to allow the nextset to be written, similar tothe sector spacing process used on magnetic disks.Comparable to conventional optical disks, the space betweenbits is 1.5 micronsin each direction, and the laser focus spot is approximately one micronacross.The data rate is 3MB/second, and the average access time forinformationretrieval is 28 seconds. For even faster access, an addresstrack is written alongone edge of the tape, to be read by a separatestationary head.67 The maximumsearch time, from one end of the tape to theother, can be achieved in one66Ibid,p.279-280.67Bradley, Optical Storage for Computers,p.98-99.43minute.68 The suppliers guarantee a storage stability of 20 years, if the mediumis stored under proper conditions. This information is unsure however, asextensive testing results have not been confirmed, and as of now only onesupplier exists for this medium. The product is being used, however, and one ofCREO’s main customers is the Canadian Centre for Remote Sensing which usesoptical tape to store data it receives from its satellites. Optical tape systems arenot inexpensive, as the CREO drive sells for about US$200,000 and a reel oftape for almost $10,000. When this is broken down into cost per megabyte, itcomes to a few cents per megabyte as one reel stores the equivalent of 100million pages, or 5,000 conventional magnetic storage tapes.69Outside of its massive storage capacity, optical tape has anothersignificant advantage over magnetic tape: it is not subject to erasure by magneticfields. The tape itself is also stronger than comparable magnetic tape, andalthough both storage media must be periodically rewound to relieve stresscaused by the incessant winding and rewinding, the stronger optical tape is morecapable of handling these stresses and is less susceptible to any damage ormechanical distortions caused by this process. In addition, the CREO system hasa built in software controller that keeps a running tab on the reliability ofthe dataeach time the data are accessed, and gives the operator advance warning whenthe data are starting to degrade. This feature has the advantage of allowing thetapes to be recopied only when it is necessary, rather than on a routine basis as isthe present case with comparable magnetic media.70The three types of optical storage media examined in this chapter,68McCormick, A Guide to Optical Storage Technology, p. 88.69j McCormick, The New Optical Storage Technology:Including Multimedia.CD-ROM. and Optical Drives, (New York: Irwin Professional Publishing,1994), p. 128.70McCormick, A Guide to Optical Storage Technology, p. 87.44WORMs, Rewritables, and Optical Tape, are all currently in use in various publicand private agencies. In addition, WORMs and Optical Tape in particular, havesignificant potential as archival storage and research media. Optical media notonly support much of the material presently created or received during thenormal course of affairs of individuals, agencies or organizations, but they willalso be used more and more as an archival storage medium for electronic andpaper records, as well as a research and preservation tool for almost any kind ofrecord found in an archives. Consequently, familiarity with optical storagetechnology is essential to both its application to present matters and to anunderstanding of future ones.45CHAPTER TWO:PRESERVATION OF OPTICAL MEDIAThe storage life of media is a topic which is critical to the missionof an archives. Archivists would like to know how much longer arecord might last in storage to plan necessary preservation.1Everything deteriorates with age, and optical media are noexception to this rule. Preservation problems occur in every medium, and withthe great storage capacity of optical storage media, data loss from mediadeterioration has the potential to affect a very large number of records. Althoughoptical storage media have not been in existence for very long, there is a body ofknowledge regarding media degradation and optimum environmental conditionsfor storage and handling. Optical storage media do not require as specific astorage environment as magnetic media, but there are nonetheless preservation,storage and handling concerns typical of optical media.As a relatively new technology, optical storage systems are stillunproven in terms of their lasting ability. Optical disks have only been availablecommercially for a decade or so, and optical tape has only been on the marketsince 1991, neither of which periods has been long enough to provide users withan experience-based estimate of media longevity. Consequently, what is knownregarding the interaction of optical storage media with the environment is based1A. R. Calmes, “Relative Longevity of Various Archival Recording Media”, inProceedings of the International Symposium: Conservation in Archives,(Ottawa: National Archives of Canada/International Council on Archives,1989), p. 207.46on a combination of previously collected knowledge about the materials used tomake the media and the results of accelerated-aging tests.Most of the elements used in the production of optical media havebeen studied for the past century and there is a considerable body of knowledgeregarding their properties. For example, tellurium, the most common optical diskbase material, was discovered in the eighteenth century, and over the years acertain familiarity with tellurium’s reactions to various environmental conditionshas been developed. A similar bank of knowledge exists for most ofthe otherelements used in the manufacture of optical media.However, the primary method used to determine the longevity andpreservation criteria of optical media is accelerated-aging testing. The specificmethodology used in accelerated-aging tests varies, but they all generally exposethe disks to very hot and humid storage conditions. Such tests usually aim tosustain a temperature of 60°-120° Celsius and a relative humidity (RH) of 90%for a brief, but previously determined amount oftime.2 All changes which occurin the media as a result ofthis treatment are noted, and mathematical formulaeare used to compute the rate at which similar changes might occur given normaluse and storage conditions. Manufacturers’ estimates regarding productreliability and storage recommendations are then based on these calculations.The three most common accelerated aging techniques used todetermine the longevity of optical media are: “steady- state elevated temperatureand humidity with Arrhenius extrapolation; elevated levels of temperature pluscorrosive gases (the “Battelle” test); and chemical stability investigations.”3The2w Saffady, “Stability, Care and Handling ofMicroforms, Magnetic Mediaand Optical Disks”, Library Technology Reports, 27:1 (January-February 1991),pp.74.3R. A. McLean, J. F. Duffy, “ICI Optical Data Storage Tape”, Presented atNASA Mass Storage Conference, 1991, p. 3.47Arrhenius Model is the main test used to determine the longevity of opticalstorage media as it “assumes that temperature and relative humidity are thecrucial independent variables that over time affect the longevity of opticalmedia.”4 Arrhenius tests are performed at “various constant conditions oftemperature and humidity”, and this, in the case of the tests performed by theNational Institute of Standards and Technology (NIST), involves storing thedisks at 70°C, 80°C, and 90°C and a RH of 90% for 4120-5711 hours. The testdisks are then read at various points during the testing process. The test resultshave showed a linear increase in error rates as the environmental conditionsworsened. This has made it possible to predict the error rate of disks at normalroom temperatures.5Similar tests performed on optical tape have exposedsections oftape to an environment of 80°C, 90°C and 95°C and 70% RH for 51days, and found a corresponding linear progression in error rates.6The “Battelle Class II” test utilizes high temperatures incombination with corrosive gases, and is intended to duplicate the “aging ofmaterials in cities and other locations where combustion byproducts form a mixof corrosive gases.”7 Before any testing, blank and written areas from the inner,middle and outer sections ofthe test tapes or disks are characterized with bit-error maps. The purpose ofthese maps is to provide a pre-test point ofcomparison against the bit-error rates ofthe same tapes and disksflçthe testshave been run. By using such controls, any changes in the test media can then beattributed to damage caused by the test’s environmental conditions. In the actual4Technology Research Stafi NARA, “Development of a Testing Methodologyto Predict Optical Disk Life Expectancy Values”, NISTSpecial Publication 500-200, (Washington, DC: NARA, 1991)p.1.5Ibid.,p.1.6ICI Imagedata, “ICI Optical Data Storage Tape - An Archival Mass StorageMedium, July 1992”, ICI Imagedata Internal Research Paper,1992,p.3.“McLean and Duffy, “ICI Optical Data Storage Tape”, p. 6.48test, the test media is held in the mixed gas environment for 60 days, as previoustests run by the Battelle Institute have determined that a 60 days exposure undertest conditions adequately reproduces the equivalent of 30 years exposure to atypical office environment. Mathematical formulae are then used again todetermine the longevity of the test media.Finally, chemical stability techniques include UV stability tests suchas the “Blue Wool Test”, which measures light fastness, and a test developed bySony for its “Century Media”, which exposes the sample to “120 hours of UVAlight at 45°C and 60% RH and is the equivalent of 70 days of sunshine”.8Temperature cycling tests are also used to determine the chemical and mechanicalstability ofthe test medium. Chemical stability can also be determined by testingthe solubility ofthe test material. In chemical stability tests on optical tape,samples were placed in a Soxhlet extraction by Delifrene, for two hours followedby another two hours in acetone, and also a Soxhlet extraction by ethanol for 72hours: after this samples and extract were weighed and analyzed for signs ofdecomposition.9These forms of chemical stability tests are particularly effectivein determining the stability of dye-polymer based materials.However, there is not yet a working environment-based estimateof the lifespan or preservation needs of optical media. Despite the findings ofaccelerated-aging tests and previously collected knowledge of optical mediaproduction materials, the accuracy of lifespan estimates is still in question as it isunclear whether disk performance under normal use conditions can be duplicatedaccurately by accelerated-aging tests and whether the lack of standardizedtesting even allows for a comparative use ofthe results of such tests.The lack of standardized testing is complicated further by the8thid,p.4.9Ibid,p.5.49optical storage media industry’s tendency to use in- house rather thanindependent testing facilities. Optical storage media testing is generallyperformed by the manufacturers of optical media rather than by independenttesting agencies. As a result, while manufacturers’ claims of product longevityare based legitimately on accelerated- aging tests, manufacturers do not oftenprovide details regarding the specific conditions under which the tests wereconducted. Test parameters, specifications regarding byte error rates for specificsurface areas rather than the entire disk surface as a whole, test methods used,quality measurement approaches, mathematical models used to extrapolate medialife expectancy at room temperature, criteria for data analysis and theexperimental stress conditions imposed on the media being tested are rarelyincluded in manufacturers’ literature regarding the life expectancy oftheirproducts. The lack of knowledge regarding the exact test parameters thus makesit difficult not only to assess the estimated lifespan of any one specific disk ortape, but to compare the performance and life expectancy standards betweendifferent types and manufacturers of optical storage media. To complicatematters fi.irther, accelerated-aging tests are more likely to have been performedduring the experimental and prototype stages of product development, andtherefore may not reflect the qualities of the final commercial product. As aresult, manufacturers claims regarding the longevity of their product have to beconsidered conservatively, rather than as an absolute product performanceguarantee.The lack of standardized testing, working-environment basedestimates ofthe needs of media conservation, and the industry’s reliance onmanufacturer-directed testing all affect both the estimated lifespan of opticalmedia and their specific preservation requirements. When assessing the lifeexpectancy and preservation needs of optical storage media, one must also keep50in mind that manufacturers’ estimates regarding optical storage media lifespansgenerally come from a closed environment controlled by the manufacturers whohave a vested interest in their product, not independent observers who may havea more objective view of the products at hand.Until the industry is capable ofproviding the user with objective, experience-based and time-tested lifeexpectancy claims and preservation guidelines, the user will have to use acombination of “buyer beware”, user experiences and a leap of faith to determinethe validity of manufacturers’ claims regarding their optical storage media. Timewill be the final judge ofthe credibility of manufacturers’ claims on the lifespansoftheir disks, but until the media have been available for 100 years, one will haveto rely on past experiences with the production materials, researchers’ estimates,user experiences and educated guesses to make our decisions on how to dealwith the preservation problems presented by optical media.MEDIA DEGRADATIONMedia degradation can occur in three categories: chemical,magnetic and mechanical. The only difference between WORM and rewritableoptical storage media deterioration is that only MO disks are subject todegradation by magnetic fields.Oxidation is the primary form of chemical deterioration found inoptical media. This problem was noted as far back as 1980, as was therelationship between oxidation and disk exposure to high heat and humidityenvironments.’0The damage caused by oxidation can be quite severe, and isobviously detrimental to the retrieval of any data stored on disks affected by thisprocess, as the data density of optical storage mediaprecludes an ability to10Saffady, “Stability, Care and Handling”, p. 74.51tolerate even small amounts of disk deterioration without a noticeable loss ofdata. Optical media store in the region of 150 to 400 million bits of informationper square inch, as compared to 50 to 69 million bits per square inch formagnetic media. Therefore, a “tracking error of one-half micron (approximately1/50,000th of an inch) in an optical disk system is enough to cause a stored bit tobe read incorrectly”, leaving little room for media degradation, and a lot of roomfor degradation-caused bit errors.” Powerful error-detection and error-correction codes can compensate for error rates “below five out of every 10,000bytes”, but once the error rate exceeds this number, the reliability of the dataencoded on the disk becomes significantly compromised. Unfortunately, mediadegradation produces error rates in excess of those correctable by such codes.Thus, it becomes necessary to use human and electronic methods to eitherprevent, prolong, or monitor the degradation of optical storage media in order tomanage the level of errors before they become too severe and the storage mediabecome unusable or unreadable.Despite efforts to the contrary, it impossible to escape the threat ofoxidation damage to optical storage media as the materials used in theirmanufacture are prone to oxidation. Metallic thin films, the materials used toproduce the recording layer ofWORM disks for example, are inherentlysusceptible to oxidation from exposure to air. Continual exposure to air results in“pinhole formation and other forms of corrosion which can significantly alter thereflectivity, transmissiveness, signal-to-noise ratios, pit formation characteristics,bit-error frequencies and other recording and playback properties ofoptical11National Archives and Records Administration, The National Archives andRecords Administration and the Long- Term Usability of Optical Media forFederal Records: Three Critical Problem Areas, (Washington, DC: NARA,1993),p.2.52media.”12 An additional characteristic of disk oxidation is weight loss, and is“associated with the formation of unidentified volatile products.”13 Oxidation isinevitable, and as shown above, its effects have a serious impact on theretrievability and readability of any data stored on media affected by this process.Oxidation of the reflective layer can also cause the recording layerto delaminate from the substrate. This form of damage can often be seen in avisual inspection of the disk, and is believed to be the result of damage to theseals on the inner and outer edges during either the placement of the disks in theovens or from the physical stresses placed on the disks by the high temperatureand RH environment inside the ovens. Fernando L. Podio, in his Development ofa Testing Methodology to Predict Optical Disk Life Expectancy Values,determined that damage from oxidation and delamination tends to affect theouter and inner tracks more than the middle tracks of the disk.14Thus, it isimperative when testing optical media for deterioration, that several track areasbe tested, as not all track sectors are subject to the same form or rate ofdeterioration.Hydrolysis, a form of media degradation caused by a chemicalreaction with water, occurs when the media are exposed to extremely highhumidity environments. This form of degradation is common to magnetic tapeformats, as it affects the binder in the recording and overcoat layers. While it ispossible for all optical media to be susceptible to this form of media degradation,optical tape with its binder and overcoat layers is slightly more subject tohydrolysis. Tests performed on optical tape, however, have shown an absence of12Jbid.,p.73.13Ibid.,p.74.14F.L. Podio, Development of a Testing Methodology to Predict Optical DiskLife Expectancy Values, MST Special Publication500-200, (Washington, DC:NARA, 1991), p. 28.53“binder hydrolysis in the optical tape recording layer after severe environmentalexposure and extraction process” and only “minor hydrolysis present in theovercoat after 3 weeks at 80°C and 80% RH.15Nonetheless, hydrolysis is a formof media degradation that can affect optical media, and environments conduciveto its development are not conducive to long-term storage and retrieval of datastored on optical media.Although MO technology employs a different means to recordinformation than WORM technology, MO disks are also affected by oxidation.Rare-earths and transition metals such as those used in MO recording media havewell- documented adverse reactions to high temperature and RH environments.Oxidation of these classes of metals has been determined to be the chief cause ofaging in MO media. For example, terbium, a rare-earths common to MOrecording media oxidizes very easily. The oxidation of terbium- ferrite thin filmwas found to significantly alter the “magnetization, coercivity and otherproperties that affect recording and playback”. In addition, the “exposure ofterbium-ferrite-cobalt to high temperatures “initiate[d] an oxidation process” thatsignificantly altered the disk’s MO characteristics.’6Accelerated-aging testsinvolving gadolinium-cobalt, gadolinium-ferrite and terbium-ferrite MO disksindicate that exposure to high humidity results in various types ofbit errors,reduced recording sensitivity and coercivity. These particular tests determinedthat the bit errors were the result of “electrochemical corrosion associated withhigh humidity” environments alone, thus eliminating dual-sided recording,recording radius or characteristics of recorded data patterns as possible causes ofsuch errors. As with WORMs, oxidation of MO disks tends to affect the outerand inner tracks more than the middle tracks.15McLean and Duffy, “ICI Optical Data Storage Tape”, p. 7.16Ibid.,p.74.54The fear of metal oxidation has, however, prompted opticalstorage media manufacturers to employ encapsulation and protective coatings-“passivation layers”-- to extend the life oftheir products. Most tellurium-basedWORMs manufacturers employ “air sandwiches” which consist of “two plattersseparated by an air-filled cavity” to protect their disks’ sensitive recordinglayers.17 The utilization of these “sandwiches” has been shown to improve thestable storage life of the disks by protecting them from environmental forces, atthe cost of only a negligible impact on the disks’ read/write properties. Theproblem with this type of encapsulation is that the protective barrier is only aseffective as the seals used to secure the “sandwich”. Once the seal has beenbroken or has deteriorated, the oxidation process begins. As there is no suchthing as an unbreakable seal for these disks, oxidation is inevitable; “airsandwiches” only delay the process.MO disks also reap significant benefits from the application ofprotective coatings to their recording layers. Silicon-based protective coatingshave been used successfully to inhibit the oxidation process on terbium- ferrite-cobalt disks. Studies have also shown that aluminum nitride coatings on terbium-ferrite and terbium- ferrite-cobalt disks have a similar effect, suppressing pinholeformation and helping to prevent a loss of coercivity on MO disks exposed tohigh temperatures for long periods of time. These aluminum nitride protectivecoatings, however, have been found to be most effective when applied to bothsides ofthe recording layer, rather than just one side.’8Metal alloying is another method by which oxidation can besuppressed, especially in WORMs. Tellurium and terbium thin films such asthose used in WORMs can become less corrosion-prone when alloyed with17Ibid., p. 75.18Saffady, “Stability, Care and Handling”,p.75.55oxidation-resistant metals. Oxidation resistance, and thus the lifetime ofthe disk, can be improved significantly when these thin films are alloyed withmetals such as boron, silicon, chromium, aluminum, rhodium or phosphorous.Specifically, the addition of selenium “completely inhibited oxidation at extremetemperatures and relative humidities.” Alloying thin films with lead was found toinhibit cracking, while the addition of platinum, titanium, beryllium, indium,boron, gadolinium or praseodymium suppressed the formation ofpinholes in MOthin films made of terbium, iron and cobalt.19Media degradation is not only found in the recording layers ofoptical storage media, but also in the substrates underneath the recording layers.Both WORMs and rewritable media coat their recording layers onto glass orplastic substrates, and unfortunately both types of substrates can suffer fromdefects which can affect their respective recording layers and thus the usefhllifetime of the media. Glass substrates are purported to have superior“uniformity, optical clarity, mechanical stability, scratch resistance, freedom fromwarping, resistance to moisture absorption and ability to withstand hightemperatures.”2°Plastic substrate advocates, however, claim their substrate ismore economical to produce, an advantage they claim overrides plastic substrate-based disks’ greater predisposition towards media degradation. Studies also showthat optical recording materials on glass substrates are less vulnerable tooxidation than those on plastic substrates as plastic substrates tend to absorbmore moisture than their glass counterparts. The less moisture absorbed by thedisk, the less opportunity for oxidation to gain a foothold and ruin the disk.21Although a user may have a preference for either plastic or glass19n,id.,p.75.20Ibid.,p.76.21Ibid.,p.76.56substrate disks, oxidation caused by defects in the substrate does not. Initialdefects in either type of substrate can accelerate the oxidation process at thedefect site. Defects affect both types of substrates, but occur more often inplastic substrates, as these have a higher incidence of initial defects and are moresusceptible to “internal cracking, swelling, shrinkage, changes in tensile strengthand formation of water-filled pockets”.22 However, some forms ofplasticsubstrate disks are better than others. Polycarbonate substrates are the bestamong plastic substrates as they do not degrade quite as quickly and aresomewhat less susceptible to moisture absorption than other types of plasticsubstrates. At the bottom of the list is polymethyl methacrylate (PMMA), whichhas an even greater tendency to absorb moisture than polycarbonate substrates,and is far more susceptible to oxidation than glass substrates. PMMA disks canalso suffer from cold flow problems. Cold flow involves gravity changing theshape of an object, and is more commonly known to occur in extremely oldstained glass windows. Over centuries, gravity has pulled the glass toward thebottom ofthe panes, resulting in thicker glass at the bottom and thinner glass atthe top of the window. A similar effect can occur when PMMA disks are placedon an uneven surface. In such an environment the shape ofPMMA disks maychange enough to cause problems with information retrieval.23 Regardless ofthe type of media, substrate materials have a significant impact on the storage andplayback stability of their respective optical storage media, something users mustkeep in mind when choosing media for their optical storage systems.Substrate materials, however, are not the only substrate- relatedfactors which affect the storage stability of optical storage media. Substandardor defective whole substrates are actually responsible for most ofthe22Ibid.,p.76.23Ibid.,p.77.57deterioration affecting the recording layer. Microscopic pits, surface roughnessand other related defects in the substrate layer oftellurium-coated disks are aprimary cause ofbit errors. Pinhole formation in MO disks are caused mainly bymicroscopic defects in the plastic substrate. In MO disks in particular, thesedefects in the substrate layer “promote the interaction of moisture with MOrecording materials, thereby contributing to pitting-like corrosion.”24 Densesmooth, uniform coating of the recording layer onto the substrate improves theresistance ofthe recording layer to oxidation and promotes the media stability ofthe disks. This is easier to achieve consistently on glass rather than plasticsubstrates, thus lowering the susceptibility of glass substrates to mediadegradation and increasing its media stability over that of plastic substrate-baseddisks. Strict quality control during disk production also assists in the eliminationof substandard or defective substrate layers and the problems they cause in thelater stages of disk production, use and eventually the promotion of mediadeterioration. Substrates are a significant element in the determination of anoptical disks’ longevity, an element which can be the determining factor in boththe accuracy of the information written to the disk and the ability to retrieve thatinformation reliably at some point in the future.As an overall judgement, however, while plastic substrate disks areless expensive, disks intended for long-term storage of information should beplaced on glass substrate disks, as they profess not only to have a greater abilityto withstand the ravages oftheir storage environments but a lower incidence ofinitial defects than plastic substrate based disks. Optical media utilizing glasssubstrates may cost more, but they have a greater storage stability and are thusbetter candidates for long- term storage use than optical storage media utilizing24Ibid.,p.76.58plastic substrates.Magnetic deterioration is another form of media degradation whichaffects certain types of optical storage media. This form of media deteriorationaffects only MO disks, as they are the only type of optical storage media whichemploys magnetic properties to record data. Magnetic deterioration occurs whenMO disks are exposed to high levels of magnetism combined with heat. Thecombination affects the magnetic orientation ofthe data encoded on the disks,making the data either unreadable or unreliable. If the magnetic field and heatsource are strong enough, the information encoded on the disk can be completelyerased. MO disks can be affected by magnetic fields stronger than 600 oersteds,but evidence suggests that the magnets have to be very close to the disk toinitiate any deterioration. Magnets exceeding 600 oersteds, however, can bepurchased in most hardware stores. Accidental erasure, either by human ormagnetic means, nonetheless, is only a problem related to MO disks.The lifespan of optical storage media is not only affected by“environmentally induced changes in [their] chemical and physicalcharacteristics”, but several other factors as well, making generalizationsregarding the lifespan of optical storage media difficult to compile. Diversity ofmedia construction and recording techniques are a significant factor indetermining the useful lifespan of any optical storage medium. WORMs andrewritables employ a large variety of recording materials, equipment and methodsof recording information. Optical disks can be constructed of metal alloys,metal-polymer combinations or dye-based materials; utilize glass or plasticsubstrates; or record information using ablative pits, bubbles, texture-change,dye-diffusion, phase change, alloy fusion or a combination of heat andmagnetism. A 1986 NARA report prepared by the National Research Council(NRC) determined that at that time there were approximately 194,400 different59combinations of optical storage media characteristics and recordingtechniques.25 The large amount of diversity within the media characteristics andrecording methods alone makes generalizations regarding disk lifespans not onlydifficult to compile, but to comprehend-- especially for those using or receivingdisks from numerous sources or creators.Media diversity goes deeper, however, than just the combinationsused in the basic construction and recordingtechniques-- the actual formulationsof the basic materials used in disk constructioncan also be proprietary. Forexample, several manufacturers may use tellurium thin films for their recordinglayers, but each manufacturer will use different tellurium alloys, and often tailorproprietary compounds specifically to one product or product line.Manufacturers ofMO media often employ a similar tactic, utilizing a variety offormulations for their specific recording materials. MO disks in particular, oftenare formulated differently depending on the way the disk will be formatted. Forexample, most manufacturers use different media for disks formatted with 512bytes than for those formatted with 1024 bytes per sector.26 Whilemanufacturers have performed accelerated- aging tests on their products, thesetests are not standardized, and thus their results cannot be easily compared withtests performed on similar forms of optical storage media. In addition, the greatdiversity of disk materials, construction and recording techniques greatlyexacerbates any attempts to create any base of general knowledge regardingthepreservation of any one type of disk. Some generalizations can be made,ofcourse, but anyone dealing with optical storage media must err on the side ofcaution, as the field’s great diversity makes it impossible to do anything elsewithout possible damage to the records stored on any one form of optical storage25ibid.,p.79.26Ibid.,p.79.60media.As a consequence ofthis lack of standardized testing and diversityofmedia construction, recording technology and media formulations, thepredicted storage lives ofboth WORMs and rewritables varies considerably. Theuseful storage life of WORMs ranges from 10 to 100 years, depending on therecording materials used, manufacturers’ claims and the results of accelerated-aging tests. Tellurium-based ablative recording WORMs have a predicted storagestability of 10 to 40 years. The earlier first- generation disks were judged to havea storage/playback stability of 10 years or so, but more recently manufactureddisks have an estimated lifespan of 30 to 40 years. The increased estimatedstorage/playback stability is due primarily to “improved tellurium alloys, mediadesigns and manufacturing technologies.”27 Disks using thermal-bubblerecording methods claim a similar storage/playback stability of 10 to 30 years.The first generation of Gigadisc 1000 WORMs have an estimated lifespan of 10years, but later versions claim a storage life of 30 years. While Sony claims thatits dual-alloy WORM “Century Media” have a storage/playback stability of 100years, accelerated-aging tests have only confirmed a playback stability of at least30 years. Dye-polymer disks have an expected storage stability of 15 years, asdo those used in tellurium-based phase change media. The WORMs used inPlasmon’s platinum-based phase change media are purported to have an usefullifespan of 50 years. Consequently, WORMs received by an archives could havean estimated storage life of anywhere from 10 to 100 years, making planning foreffective conservation and preservation procedures a difficult task.Optical tape, while the newest member ofthe WORM family, hasthe longest predicted lifespan. ICI Imagedata tests have calculated a media27Ibid.,p.80.61lifetime of more than 30 years “in the presence of corrosive gasses” (the BattelleTest), and a chemically stable lifetime in excess of 300 years, under ideal storageconditions of 20°C and 60% RH. The latter prediction was based on results fromArrhenius testing and comparisons with the tests performed on Sony’s “CenturyMedia”28Unlike WORMs or optical tape, however, rewritables must havean identical shelf and playback stability rate, as these disks must support both therecording of new data and the retrieval of old data. Overall, the reliablerecording and playback life of MO disks ranges from 10 to 25 years dependingon the substrate used and the manufacturers’ claims. MO disks utilizing plasticsubstrates generally have a usefhl shelf and storage stability of 10 years.However, MO disks employing glass substrates have an estimated lifespan of 15to 25 years. Rewritable disks using phase change recording technology have anestimated storage/playback stability of 10 years. Rewritables have a significantlyshorter estimated lifespan than WORMs, a factor which must also be taken intoconsideration when determining the conservation and preservation plansregarding any institution’s, agency’s or archives’ optical storage media needs andconcerns.Unfortunately, all this speculation regarding the lifespans anddurability of optical storage media must take into consideration the continualgrowth and evolution of optical storage technology itself. The technologyinvolved in both the creation of the disks and more importantly their drivesystems is new and is constantly changing, making estimates regarding thelifespans of any one optical storage media a bit of agamble at the best of times.28“ICI Optical Data Storage Tape”,p.3, 6. ICI Imagedata prefers, however,to use a more conservative estimate of 100 years as thisnumber takes intoconsideration more generously “the large errors associated with calculation ofactivation energies and extrapolation of such predictions.”62As such, it is likely that the elements that make up an optical disk or tape will lastlonger than the systems needed to retrieve the data recorded on them. Thus,information stored on Sony’s “Century Media” may be technically readable 100years from now, but realistically, the optical disk drives and the software neededto read the data will have been long gone, rendering the information stored onthe disks unreadable.In terms of optical drive systems, the software and hardwarecomprising the drives typically have a useful life of approximately ten years.While manufacturers generally provide their next generation products with somebackward comparability, this is not necessarily the case. The STORLORDoptical disk storage system used by the National Archives of Canada (NAC) is anexample of a manufacturer not providing this backward compatibility, leaving theuser stuck with an obsolete, and eventually insupportable information storagesystem. In June 1992 the manufacturer of STORLORD released an upgraded butnot downwardly compatible version of its disk drive. The manufacturer isrequired by law to support the previous disk drive system for seven years, butthis “leaves the NAC with no obvious migration path.”29 Althoughmanufacturers are required by law to support their products for seven years afterthe product has been discontinued, for archival purposes seven years hardlyprovides permanent access to the information stored on such systems. Thediscontinuation of equipment is not without other precedents, as the presentunreadability of “seven-track magnetic tapes and hard- sectored eight-inchdiskettes” prove beyond this the shadow of a doubt.3°Therefore, users must becareful to choose reputable and stable manufacturers for their optical storage29Electronic Records Coordinating Committee, Historical Records Branch,Report of the Working Group on Conservation Standards and Technologies,(Ottawa: National Archives of Canada, 1992),p.5.30Safl’ady, Optical Storage Technology 1992,p.7.63systems, upgrade their equipment and migrate their data tokeep both usable.Otherwise, the information stored on such obsoletesystems becomes almostimmediately unreadable and unusable.As such, the hardware and software dependency of optical storagesystems does not give the manufacturers of disks with long storage stabilityestimates any great edge over those ofthe competition. No matter whatrecording technology is used, is likely that if the information recorded on theoptical disk or tape is intended to be readable for morethan approximately tenyears, the information will have to be translated to other,newer media in order topreserve the information written to the disks. Thus, the storage stability ofthemedium is not really a significant factor, as the information on it will likely haveto be transferred long before the expected lifetimeof the disks themselves haveexpired. The disks or tapes may last a hundred years, but if the hardware andsoftware needed to read the information on them no longer exists, the longevityofthe storage medium is insignificant, as the information it was storing hasbecome unreadable. Unreadable information is useless, regardless of its storagemedium and its longevity.STORAGE AND HANDLiNGProper storage and handling of optical storage media is essential toguarantee and prolong its usefulness as an information storage medium.Whileoptical storage media do not require as specific a storage environment as docomparable magnetic-based storage media, there are recommended storage andhandling procedures for optical media. Despite theinherent hardiness ofthemedium, it is still subject to damage caused byimproper storage and handlingprocedures or techniques.Although we do not know the ideal temperature or RH conditions64for long-term storage of optical storage media, we do know that hot and humidconditions promote oxidation and corrosion ofWORMs, optical tape andrewritable disks, particularly those which use metallic thin films in their recordinglayers. Passivation layers and corrosion- inhibiting alloys provide someprotection from oxidation, but as of yet there is no way to prevent oxidation fromoccurring; we are only able to postpone the inevitable. All-encompassing storagespecifications for optical storage media are complicated by the great variety ofcombinations ofrecording technologies used by WORMs and rewritables. Whatwe are left with are manufacturers’ recommendations regarding conditions underwhich they believe their equipment will perform reliably. Manufacturers’recommendations for acceptable working conditions for their media range from10°C to 60°C with a maximum rate of change of 10% to 20% per hour.Recommended RH ranges from 10-80% with a rate of change similar to those fortemperature. The recommended environmental conditions for long-term storageare even broader, allowing a temperature of -10°C to 50°C and a RH of 10-90%.31Although the estimated storage requirements for optical media arefar less stringent than those needed for magnetic media, and fall within the rangeof environmental conditions found in the vast majority of homes and offices, thisdiversity can still present storage problems. Such a wide spectrum of acceptablestorage environments presents the advantage of allowing the storage facility to beflexible in its storage environment, but also the disadvantage of presenting thestorage facility with a wide variety of storage requirements for its various opticalmedia. An assortment of storage requirements can be expensive to maintain,31Safl’ady, “Stability, Care and Handling”, p. 84. ICI Imagadata suggests amore specific 18 degrees C and 70% RH as the ideal storage conditions foroptical tape. (ICI Imagedata, “ICI Optical Data Storage Tape”, p. 6.)65particularly if individual media requirements do not fit easily into the storagespecifications demanded by other media within the institution’s holdings.High temperatures and RH affect not only the recording layers ofWORMs and rewritables, but also their substrate layers. As such, optical disksemploying plastic or PMMA substrates should not be used in areas affected byhigh humidity as they tend to absorb moisture more readily than glass substratebased disks. Under such conditions, plastic or PMMA based disks would have amuch higher rate of oxidation and corrosion than comparable glass substratebased disks.Optical tape is similarly affected by high temperatures andhumidities, as it is also based on a polyester substrate. High temperatures andrelative humidities can cause the polyester base film to warp and become brittle,preventing the tape from being rewound onto its reel and being read by theoptical reader. The Mellinex base layer used in optical tape is extremely stable,but care should be taken not to expose the media to conditions which wouldcause the base film to deteriorate.32Circumstances of high humidity, however, are not only limited togeographic areas subject to natural high humidity conditions. High RHconditions can easily be generated inside an office environment by common officeequipment and furnishings. Simply having liquids near the optical storagemedium on a regular basis can increase the RH in that immediate area, especiallyifthe liquids are accidentally spilled on the disks or tapes themselves. Inaddition, disks should not be stored near kettles or any other water vapourcreating devices as this also increases the RH in the immediate vicinity of thetapes or disks.32ICI Imagedata” ICI Optical Storage Tape”,p.4.66Heat and direct sunlight also have a significant impact on theeffectiveness and longevity ofoptical media. Optical storage media should not bestored in direct sunlight, near radiators or other intense heat sources, as this canaffect both the recording and substrate layers. They also should not be stored ontop of their drive systems, as this exposes the media to both heat and dust.Dust and dirt are two ofthe most common elements in any officeenvironment, and two of the most damaging to the proper use and storage ofoptical media. Dust and dirt affect the reflectivity ofthe disk, causing playbackerrors. Dust on a disk or tape causes the optical reader to skip, creating an effectroughly analogous to the skipping of a phonograph record. These conditions canmake information retrieval more difficult if not occasionally impossible, thusseverely limiting the useflulness of the media in question. Consequently, disks,tapes and their drive systems should not be placed near dust and dirt producingequipment such as photocopiers, printers and ash trays, unless one is prepared toclean the disks regularly or have the media affected by the dust and dirt createdby these devices. In short, keep the disk storage area as clean and dust-free aspossible, and only operate optical storage media on systems which are in goodoperating condition and are cleaned and maintained regularly.Contaminants as a whole cause a significant amount of damage,both permanently to the disk and personally irritating to users of optical storagemedia. There is a reason most optical disks are stored in cartridges; to keep themas free as possible from possible contaminants. Consequently, users should nottamper with the disk cartridges, as this behaviour makes users as much of acontaminant as dust, dirt and spilled coffee and just as damaging to the effectiveoperation of the optical media. While the cartridges are as tamper-proof aspossible to prevent these sorts of problems, the cartridges are not hermeticallysealed. As a result, dust, the perpetual enemy of optical disks, can indeed invade67the cartridge and wreak havoc on the disk sheltered within. If this happens, thedisks should be cleaned immediately with the disk cleaner recommended by themanufacturer for the specific disk in question in the manner specified bythe manufacturer. There are so many different types of disks in themarketplace that swapping disk cleaners may not be a good idea and couldactually cause more harm than good. It is better to be safe than sorry and followthe manufacturers’ directions when attempting to clean optical storage media.Although WORMs and rewritables are typically encased incartridges to prevent their recording surfaces from scratches, skin oils, dust,fingerprints and other surface debris, they are still subject to damage from roughhandling. Disks should not be squeezed, placed under heavy objects, bent, orotherwise wrenched out of shape. This is especially important when placing thedisks in and out oftheir drives and when the disks are placed in storage. Careshould be taken to ensure that disks are not wrenched in and out of their drives,are kept out of their drives until they are ready for recording or playback, and notleft in their drives unless actually in use. Disks should be stored upright, or inboxes which “contain activated carbon and molecular sieves along with alkalinebuffering” to capture and neutralize the oxidative and acidic gasses found in ourpolluted city air.33Optical tape should be handled in a similar fashion, except that as atape rather than enclosed disk, it must be handled more careflully. Optical tapehas a strong polymer base which can withstand a significant amount of tension,but tugging and wrenching the tape will nonetheless damage the media. Like33E-mail from William K. Hollinger to Archives Listserve 13 February 1994.Hollinger cites an article titled “Protection of Archival Materials FromPollutants: Diffi.usion of Sulfur Dioxide Through Boxboard”, Journal of theAmerican Institute for Conservation, 32:1 (Spring 1993) as his source for thisinformation.68optical disks, optical tape should be stored upright, but supported from the insideand outside to equalize the pressure on the tape within its storage canister.Placing any form of barcode, label, or ink on a disk is also notrecommended. The solvents in the adhesives on the barcodes or labels have beenknown to eventually eat through the disk’s protective layer, severely affecting thedisk’s read/write capabilities and lifespan of the disks. Marker and pen ink cancause the same problems, and thus should also be avoided.While WORMs or dye-polymer/phase change-based rewritablesare not affected by magnetic fields, MO disks are “subject to accidental erasurethrough inadvertent exposure to magnetic fields of sufficient coercivity”.34Whileinadvertent erasure is unlikely, as a significant heat source is also necessary toalter data on such disks, exposure to any permanent magnets or objects whichgenerate magnetic fields must be prohibited in areas using MO disks.Optical disks in long-term storage should be inspected on a regularbasis, annually or whatever is practical, to facilitate the detection of mediadeterioration. ICI Imagedata recommends a wind interval of five years foroptical tape stored under ideal conditions. ICI Imagedata considers this to be aconservative estimate, and expects that “further analysis will extend thisprediction to ten years or more.”35 Inspections should include the following: avisual inspection ofthe disk and its housing/cartridge, and the retrieval of asample ofthe data stored on the medium. Ifthe number of disks or tapes instorage is prohibitively large, a sample can be regularly tested, or a test/controlmedia can be made using the same system and recording materials as the disk(s)or tape(s) in the holdings. Ifthe test media is deteriorating, then the rest of theholdings corresponding to the test sample would then be inspected for damage.34Saffady, “Stability, Care and Handling”, p.85.35ICI Imagedata, “ICI Optical Data Storage Tape”,p.8-9.69If deterioration is present, the data on the affected media should be copied ormigrated as soon as possible. To avoid system and media obsolescence, datashould be migrated regularly in order to extend the life ofthe informationrecorded on the optical storage media.Optical storage media also require care during shipping. TheANSI 1987 environmental restriction standards for 5.25” WORMs recommend ashipping temperature of -20°C to 54°C. These recommendations are intended tocorrespond to conditions found during truck or train transport and are notintended to be of more than two weeks duration.36 To prevent accidentalexposure to magnetic fields while MO disks are in transit, there should be athree-inch barrier between the disks and the sides of the transport container.Luckily, there are special containers for just this purpose.37 Once the disks ortapes have arrived at their destination, they should be allowed a 2 hourconditioning time before they are placed in their permanent storage containers, toslowly acclimatize the media to their new conditions. This practice should alsobe followed prior to the optical storage media being put into use. This procedurehelps to lessen the impact of any temperature or humidity changes between thetransport and storage conditions or the storage and use conditions. It also aids inpreventing any condensation from forming on the disks or tapes as the result ofsuch changes in temperature or humidity.38A large part of an archives’ duty is the preservation of the records36U.S. General Services Administration, Information Resources ManagementService, Applying Technology to Record Systems: A Media Guideline - May1993, (Washington DC: General Services Administration, 1993),p.37.37Saffady, “Stability, Care and Handling”, p.86.38The ANSI 1987 Environmental Restrictions for 5.25” WORMs alsorecommends temperature gradients of 10, 15 and 20 degrees Celsius foroperation, storage and shipping respectively, and air pressure from 0.75 to 1.05bars to prevent disks with “air sandwiches” from warping or splitting open.Applying Technology to Record Systems, p. 37.70entrusted to its care. All records, regardless ofthe media on which they arestored, deteriorate with age making the need for proper preservation, storage andhandling of records a vital one in all archival institutions. With paper records,this entails maintaining proper temperature and humidity controls, the use ofacid-free containers and light controls among other considerations. Like anyother media, records stored on optical storage media also require certainenvironmental conditions to ensure the preservation of the disks and tapes andthe data stored on them. Unlike paper, however, optical storage media alsorequire the maintenance of the systems needed to read the disks and tapes as wellas the medium itself. Optical storage media have the advantage of a huge storagecapacity in a very small physical space, but are dependent on computer systemsto access and read the stored data. The advantage of huge storage capacity,however, also has the disadvantage of huge data losses if either the media or thehardware and software systems needed to read the disks or tapes deteriorates.As such, the proper preservation, storage and handling of records stored onoptical storage media are crucial issues as the data losses from media degradationcould be vast.Optical media have not been in existence for long enough toprovide us with an adequate model regarding their longevity or potentialdeterioration problems. Nonetheless, we do possess a certain amount ofknowledge regarding the chemical composition ofthe media and the results ofaccelerated-aging tests on the various types of optical storage media. Presentestimates regarding longevity and deterioration patterns are all based oninformation gained from the above sources combined with the limited real-lifeexperience users have had with optical storage media. We know that most ofthemetals used in the composition of optical storage media, tellurium in particular,are susceptible to oxidation. We also know that there is no way to prevent71oxidation; we are only able to devise materials and practices capable of retardingthe oxidation process. Unfortunately, most ofthe knowledge regardingaccelerated-aging tests has been gained at the request of optical mediamanufacturers, and often at the prototype rather than the production stage of themedia. This raises the question of the validity of the test results, as well as theapplicability ofthese results to regular-use conditions. Standardized, impartialtesting procedures and programs would facilitate greatly the legitimacy ofmanufacturer-based claims regarding media longevity and deterioration patterns.In addition to oxidation, optical storage media substrates aresusceptible to damage, especially polymer- based substrates. These particulartypes of substrates are more vulnerable to high temperatureand humidityenvironments, and are more likely to exhibit defects which affect the reflectivityof the recording layer. Glass substrates are less prone to oxidation and do notexhibit the same level of defects, but are more expensive to produce. As such,the user is well advised to be aware of the substrate materials used in theiropticalstorage media, as this affects the preservation, storage and handling demands ofthe media.Diversity of media construction and the systems required to readthe media also affect the preservation, storage and handling needs ofopticalstorage media. At the present time, there are many different types of media andrecording techniques available on the market. In addition,the fact that recordssubmitted to an archives are at the end oftheir life cycle indicates that theformats used in both the media construction andrecording techniques may bethose which are no longer in common use. Thisproblem can exacerbate thepreservation and storage requirements ofoptical media within an archives, aseach type of optical storagemedia may have slightly different preservation andstorage needs. Fortunately, interms of storage, optical media are remarkably72hardy, and require much less maintenance and specialized environmental controlsthan most media. General office conditions are usually adequate for the long-term storage of optical media, provided the media are kept dust-free and arestored at somewhere between 18°C-20°C and 50-60% RH, the general consensusregarding optimum storage conditions for optical media.The storage and handling requirements of optical storage mediaowe more to common sense than technical specifications. Thbewdal8°C-20°C and 50-60%surprisingly rugged and is not subject to the same temperature and humidityconditions as are similar magnetic-based storage media. While excessively hotand humid conditions do promote oxidation and polymer substrate damage,environments common to most workplaces do not pose much of a threat tooptical media. As long as the disks and tapes are kept contaminant free, arestored upright, and are not subject to being bent, scratched, warped or otherwisemishandled, they should last between 10 and 100 years, providing the hardwareand software needed to read the disks or tapes are still available.Generally speaking, optical storage media have a storage lifeofbetween 10 and 100 years. Sony’s “Century Media” and ICI Imagedata’s ICI1012 Optical Tape have the longest predicted lifespans, 100 and possibly inexcess of 300 years respectively. The others fall between 10-50 years, with glasssubstrate-based WORMs beating out polymer substrate-based MO disks. Allthis, of course, depends on the availablilty of the software and hardware neededto read the information stored on the various forms of optical storage media.System obsolescence can likely be guaranteed to occur every 10 years, but withsystem upgrades and backwardly compatible software, the information stored onan optical disk or tape should be accessible as long as the medium itself isundamaged. This situation, however, is an ideal one, and regarding the lack ofstandardization within the world of optical storage media, likely to be the73exception rather than the rule in many cases. Optical storage media present agreat window of opportunity for archivists in terms of making delicate recordsmore accessible, solving storage problems, and providing a long-term stablestorage media for data presently stored on less stable media, but if the softwareand hardware needed to read the records stored and migrated onto optical mediaare not available, all the preservation, storage and handling techniques in theworld will not make the information stored on obsolete forms of optical mediaaccessible.74CHAPTER THREE:OPTICAL STORAGE MEDIA:ARCHIVAL APPLICATIONS M’TD IMPLICATIONSSignificantly, the use of optical disc technology has progressedwithin the span of a decade from a tentative field of investigation toa practical and effective means of assisting archivists andinformation specialists in the preservation and control of animportant segment ofthe nation’s cultural heritage.., and spells anew chapter in providing access to the rich visual collections oftheNational Archives of Canada.1There are many different ways archives can use optical storagetechnology, each with its own access, preservation and archival applications andimplications. In one sense, records stored on optical media are no different fromthose stored on any other medium, however, the optical medium’s dependency onmechanical means for access, storage and readability introduces a whole set ofproblems, advantages and disadvantages not necessarily presented by moretraditional media. This dependence on system hardware and software makesboth the preservation of and access to records, either initially stored on or latertransferred to optical media, more complex than those records stored on othernon-machine-readable media. Problems related to the regular migration of data,quality control, regulated access, copyright requirements, and other legalrequirements, must be taken in to consideration in addition to the more obviousmechanical problems associated with machine readable records. Storing records1G. Stone and P. Sylvain, “ArchIVISTA:A New Horizon in Providing Accessto Visual Records ofthe National Archivesof Canada”, Library Trends, 38:4(Spring 1990),p.750.75on optical media can have both great benefits and crushing disadvantages, and itbehooves institutions, to be aware of all the factors involved in the preservation,access and implementation of any optical media program.APPLICATIONSThe first consideration of any archivist dealing with records storedon optical media must be the appraisal ofthe records. This applies to bothrecords stored on optical media by their creator(s) and those on a differentmedium destined to to be transferred by the archives to storage on optical media.As with records stored on any media, not all records delivered to an archiveswarrant permanent preservation. Records stored on WORMs and Optical Tapeare no exception to this rule, despite the fact that records stored on these formsof optical media are unalterable and thus considered “permanent”.Notwithstanding the tremendous storage capacity of optical media, not only is itimpossible to keep physically and control intellectually every record created byany creator or agency, but this would defeat the purposes themselves of archivalpreservation.However, the very “permanence” of records stored on WORMsand Optical Tape can present a problem when appraising them. Records storedon these two optical storage media cannot be erased, only augmented. As aresult, if during the appraisal process the archivist determines that not all therecords stored on one ofthese two media are worthy of permanent retention,there is not an easy way ofdisposing of the unwanted records. However, asrecords on these media are accessed by indexes often stored magnetically, thearchivist can alter the indexes and finder programs to prohibit access to theunwanted records. Although this does not eliminate the number of recordsstored on the medium, it limits the need for establishing and maintaining76intellectual control on all ofthem. This procedure can also be used as a way tolimit access to records with access restrictions. A copy ofthe original index andfinder programs would remain with the archivist or others who have the securityclearances to see all related restricted records, while another abridged versionwould be made available to the general public. Unfortunately, this is not feasibleifthe indexes and finder programs are written onto the WORMs or Optical Tape.In these cases, it might be necessary to create new abridged versions ofthesearch programs, and note in the fonds descriptions that this has indeed beendone. In any case, the unwanted records will still remain on these “permanent”forms of optical media, a factor which archivists must take into considerationwhen appraising them.One way to get around the drastic solution of keeping all ornothing would be to work with the agencies responsible for the creation of therecords during the earlier stages of the records’ life cycles. Appraisal of recordsintended for permanent retention could really begin before the records are placedon WORM disks or Optical Tape. As part of a well-designed electronic recordssystem, vital records could be identified as soon after their creation as possible,then flagged for fi.iture transfer to non-eraseable optical media for permanentpreservation. Otherwise, it is simply too easy for large amounts of non-valuabledocuments to be transferred onto non-eraseable optical media, and thus bepermanently preserved.Archivists must take an “active approach to the development andinstallation of electronic office systems” and work with records managers tochoose software which will identify vital records at the time oftheir creation, andflag them for transfer to non-rewritable forms of optical storage media.2 By2K. Gavrel, Conceptual Problems Posed By Electronic Records: A RAMPStudy, Prepared by Katharine Gavrel for the GeneralInformation Programme at77providing guidelines for organising electronic records, archivists and recordsmanagers will not only facilitate the fast and efficient retrieval of current material,but will also expedite the ability of the system to separate the wheat from thechaff and preserve on WORMs or Optical Tape intended for the archives onlythose records valuable enough to be permanently preserved. Involving the usersin both the development and implementation of such a program would also helpthe program, secure its proper implementation and restrict the system’s andoperators’ ability to destroy valuable records.3Technical analysis must, however, be combined with contentanalysis for proper appraisal to take place. Archivists must also realise thenecessity for maintaining not only the technology required for access to both theirown information and that which has been entrusted to archival custody, but thedocumentation connected with the systems. Identif,iing and preserving all systemdocumentation, now called metadata, is necessary to preserve the context inwhich the information was gathered, information about the creator(s), the roleplayed by all persons involved with the system, and the links between the systemand other databases, sources of records and information.4Documentationprovides access to both the codes used to represent the data stored on the opticalmedia and the locational arrangement ofthe data on the disks or tapes, twoelements vital to the understanding, interpretability and migratability of data.Optical media, or their accompanying software, equipped with InformationResource Dictionary Systems (IRDS) will have all the information elementsnecessary to place the entire system within its administrative, structural andfhnctional context. This, in addition to an open systems architecture, is not onlyUNISIST, (Paris: Unesco, 1990),p.21.3Ibid. p. 21.4Ibid,p.27.78necessary to ensure future access to and interpretability ofthe data, but to allowinformation to pass successfully from one generation of optical disk-based accesssystems to the next and still retain its authenticity.5MIGRATIONHowever, it has to be born in mind that no media is permanent; alldeteriorate and/or can be destroyed. Paper can burn or deteriorate due toexternal and internal chemical factors, magnetic media can suffer from “stickytape syndrome”, and despite the use of oxidation resistant alloys and barriercoatings, optical disks will also eventually undergo chemical and physical changeswhich will make them unfit for both the recording of new data, or the retrievaland deciphering of earlier data. These changes to optical media may be causedby environmental factors, manufacturing defects, or by damage caused byimproper handling ofthe disks themselves. Either way, the “permanent” storagecapabilities of optical media are not very realistic. The lack of “permanency” isparticularly significant to information stored on machine-readable media, as it isnot most often the deterioration of the actual media that constitutes the mainproblem, but the unavailability of the technology needed to read the informationstored on the media. With optical storage media, the medium itself is quite stableand does not require an environment more controlled than that of a normal officefor storage purposes, but the hardware and software systems needed to read themedia become obsolete every few years. Paper documents, as long as the writinghas not faded too much, can be read with only the aid of a magnifying glass and alittle guesswork. Optical media cannot be read without the appropriatetechnology. Therefore, the meaning ofthe concept of “permanence” has been5M. Hedstrom, “Optical Discs: Are Archivists Repeating the Mistakes ofthePast?”, Archival Informatics Newsletter, 2:3, (Fall1988),p.52.79changed by technology, and linked to the readability of data stored on variousmedia. Ifthe systems used to read the records are unsupportable, the recordsstored on the corresponding media may also be unreadable. Consequently, thematerial support ofthe record, especially if machine-readable, has become lesssignificant as a factor in establishing the permanence of the record. In order forthe data stored on optical media to be permanently accessible and readable, theconcept of “data migration” must come into play. The medium becomes lessimportant than the information recorded on it; thus the medium can be changedand the information transferred to another medium, as long as the particularsregarding the original medium and the formatting of the original record arerecorded on the new medium.Migrating data simply means transferring them from one mediumto another. Usually this is performed as a conservation measure to save datastored on an obsolete or soon to be obsolete medium or machine-readablesystem. This is often done with records affixed to magnetic tape to allow therecords to be read on the next generation of either computer software orhardware or audio systems. This procedure is analagous to re-recording musicfrom a vinyl record to a tape cassette. In this example, the music is transferredfrom an older medium to a newer one in order to prolong its playability.A similar process can be carried out with records on magnetic tapeor disk in order to preserve their readability, and to make their conservationeasier. Optical media do not require the specialized environmental controls thatmagnetic media do, thus migrating the data to optical media can make them moreeasily accessible but also more easily preserved physically.Of course, the migration procedure would affect the status oftransmission of the records, as they would no longer be in their original formonce they have been migrated to the new media. This could present a problem80regarding the legal value of records migrated and stored in this manner. At thepresent time, the only two media “generally admissible in evidence for allpurposes for which the original record would have been admissible” are paperand microfilm.6Although records stored on microfilm and optical storage mediashare the characteristics of existing in a compact space which allows for easyretrieval, microfilm stores images using analog technology while optical mediaused digital technology. Microfilm stores “miniature likeness of an originaldocument” while optical media store “data from which a document, like theoriginal document in all visual respects may be produced.”7As a result, recordsstored on optical media qualif’ as copies in the form ofthe original but undercontrolled circumstances can have the force of originals as do records stored onmicrofilm. For the most part, however, courts will accept copies reproducedfrom optical disk if the following elements are present:a) the original is no longer available;b) “the copy was made with the intention of standing in theplace of the original;c) the absence of the original is adequately explained;d) the circumstances of the making ofthe original and of thecopy are adequately explained.”8Nonetheless, the manner in which these elements are taken into account will varywith the evidentiary problems presented by each record and with the lawsapplicable to each case.6R. M. Anson-Cartwright et al., Records Retention: Law and Practice(Toronto: Thompson Professional Publishing, 1994), p. 6-9.7Ibid.,p.6-9.8Standards Committee on Microfilm and Electronic Image as DocumentEvidence -(dIMS), “Draft: Microfilm and Electronic Image as DocumentaryEvidence”, in R. M. Anson- Cartwright et al, Records Retention: Law andPractice (Toronto: Thompson Professional Publishing, 1994), p. C- 25,Appendix C.81As there are no standards for optical media records asdocumentary evidence, records stored on optical media do not come under thesame statutory provisions as those for microfilmed records.9 Prints frommicrofilmed records are “generally accepted as evidence for all purposes forwhich the original record would have been admissible.” Since optical media donot employ the same technology as photographic film, prints generated fromoptical media are not considered to have the legal status of original records. Atthe present time there is a working group trying to establish a standard forrecords stored by digital means. The draft of CANICGSB-72. 11 -M92, a standardfor microfilm and electronic image as documentary evidence, has been offered,but is not yet at its final stages. Until standards are in place for electronic imagesas documentary evidence, the legal admissibility of optical media recordspreserved by an archives depends on the following conditions being met:a) use of the optical storage system as part of a regular,established archival practice in order to keep permanentrecord of the migration of the records in question, andstoring records on optical media as part oftheorganization’s “usual and ordinary course of business”;b) use of the optical storage system in relation to classes ofdocuments;c) destruction ofthe original records in the presence of anemployee/archivist with the qualifications and authorizationto oversee and perform such proceedings as an ordinarypart of his or her duties;d) preservation ofdetailed records regarding the operation ofthe optical storage system;e) preservation of detailed records regarding the “methods andprocedures for creating, verifying, storing and retrievingdocuments”;f) preservation of accurate and secure bibliographic andbiographic information relating to the images stored on theimage system;f) and preservation of “originals of bills of exchange,9Anson-Cartright, Records Retention,p.6-9.82promissory notes, cheques receipts, instruments, agreementsor other executed or signed documents for six ar’°Adherence to these conditions, if technology continues to advance as quickly as ithas in the past few decades, is necessary for any organization’s record keepingsystem, and any archives’ data migration program if either are to preserve thelegal admissibility ofthe officially stored records in their custody.PRESERVATION AN]) ACCESSData migration onto optical storage media can also be used for thepreservation of and access to fragile or delicate records. Such records can easilydeteriorate fi.irther with use, and highest used records can become delicate orfragile simply as a result of being used often. By placing images ofthese records,or migrating/copying them onto optical storage media, both could be accessedwithout taking the originals out of their special preservation areas. Humancontact with such items would be kept to a minimum, thus safeguarding theconservation and preservation needs ofthe original documents. The records, ofcourse, would not be locked away permanently once the optical image had beenmade, but would be available to researchers whose work demanded that they seethe detail of the original record. Copies made from the disk or tape would alsoallow for a wider dissemination without harming the original record by allowingfor their placing on a local or wide area network. While computer-generatedimages are not as identical to the original, even if sometimes more detailed, viaoptical media would allow a certain degree of accuracy in concert with a greatincrease in the accessibility of fragile or delicate items.10Thid., p. C-23; Anson-Cartwright, Records Retention,pp6-9, 6-10. For amore complete and detailed description of the suggested evidential requirementsfor imaging systems please see Appendix C of Anson-Cartwright, RecordsRetention, “Draft: Microfilm and Electronic Image as Documentary Evidence”.83Optical storage media as a preservation tool have been usedsuccessfully in the Optical Digital Image Storage System (ODISS) project at theNational Archives and Records Administration (NARA) in the United States, andin the ArchiVISTA project carried out by the National Archives of Canada(NAC) at the Canadian Museum of Caricature. Both projects were initiated totest the viability of optical storage systems as a solution to some of thepreservation and reference problems associated with highly used, delicaterecords.The ODISS project was initiated in 1984 as a way of solving thereference and preservation problems concerning one of the largest and most usedcollections ofrecords in NARA’s custody: the 82,000 cubic feet of Pension,Bounty Land Grant, and Compiled Military Service Records. These consist of“the military service and pension application records extending from the time ofthe American War for Independence... to . .the period just prior to America’sentry into World War I.”11These records are heavily used and as a result have sufferedsignificant damage. In 1983, for example, a staff of twenty-seven was needed tohandle the 116,000 mail and the approximately 80 daily walk-in requests. Acombination of the high use and age of the documents has resulted in thefollowing problems: 65% have minor physical problems, 10% have majorproblems. In addition, 95% are either completely or partially handwritten and42% suffer from low contrast and thus reduced legibility.12 Previous attempts tomicrofilm parts ofthe collection were not successful, as the age and poor11W. M. Holmes, Jr., “The ODISS Project: An Example of an Optical DigitalImaging Application”, in Proceedings of the International Symposium:Conservation in Archives (Ottawa; National Archives of Canada/InternationalCouncil on Archives, 1989),p.233.12Holmes, “The ODISS Project” pp. 233-234.84condition of the documents resulted in poor quality products. Eventually, themicrofilming project was halted as the condition ofthe records made itimpossible to produce acceptable microfilm copies.In 1984 NARA decided to try a pilot optical media project usingsome of the Pension, Bounty Land Grant and Compiled Military Service records.They represented the types of records which might benefit most from beingscanned onto optical media as they were highest used, fragile, and because oftheir low contrast writing, difficult to microfilm successfully. The main purposesof the project were to:a) determine the feasibility, costs and benefits of digital conversion ofboth original documents and microfilm copies;b) identify what problems were to be encountered with such a system;c) determine the most efficient procedures for accomplishing aconversion;d find the optimal mix of automated conversion with human qualitycontrol and intervention to produce acceptable results;e) determine the optimal scanning density for documents consistentwith production legible images while minimizing storagerequirements;f) and determine public reaction and acceptance to the use of such asystem.13In addition to the purposes mentioned above, digital enhancement ofthe scannedcopies would also have attested to the capability of the procedures to producemore readable copies. Once stored on optical media, the records could also beplaced on either a local or wide area network, effectively increasing access to theoptically stored copies, while protecting the more fragile originals. The basicchallenge was to see if technology could assist in the preservation of and accessto hundred and twenty year old handwritten records.In 1985, a test sample using 400 cubic feet of documents from the13Ibid., p. 235.85Tennessee Confederate Compiled Military Service Records (CMSR) was chosen,as these records were of an age and physical condition comparable to those in thelarger collection. The CMSR records had also been microfilmed, and this wouldhave provided a method of comparing the images stored on optical media withboth the microfilmed copies and the original documents.Part of the original objectives for the ODISS project was to testthe feasibility, costs and benefits of migrating the CMSR documents onto opticaldisk. As such, the preparation ofthe documents for scanning was also part oftheexperiment. The document preparation procedures for scanning onto optical disk,however, were found to be similar to pre-microfilming procedures, except thatparticularly fragile documents were placed in polyester sleeves for protectionduring the scanning process. To scan the documents, four high speed grey scalescanners were used, three for paper records, one for microfilm. The Photomatrixscanner had the ability to scan 20 documents per minute at 200 dots per inch(dpi), a standard which was acceptable for 98% ofthe documents scanned. Twolow speed scanners were also used for more fragile documents. A highresolution monitor attached to the system provided immediate feedbackregarding the quality of the record just scanned. This allowed technicians toidentify immediately those records which needed to be rescauned. The imageenhancement feature allowed documents to be enhanced in three ways:character, which brightened the light parts of the document and darkened thedocument’s dark parts; photograph, which increased clarity via half-tones; and acombination ofboth for records with significant problems in both areas.’4Although a throughput of 3800 pages per day was predicted, thenecessity of hand positioning some documents and the different sizes of14Ibid.,p.58.86documents allowed NARA staffto scan onlyil58 documents per day.15 Toachieve the amount ofthroughput initially expected, it was necessary to useautomatically adjustable scanners. Once scanned, the images were stored on 12”WORM disks, each with the capacity to hold 80,000 images and preserved in afifty disk jukebox with a capacity of 109 gigabytes or approximately 2.42 milliondocument images.16 The indexes were stored on magnetic disks, as this made iteasier to both correct misfiled or mislabeled images and update the index.The ODISS Project highlighted several advantages anddisadvantages to the use of optical storage media as a preservation and accesstool. One of the main advantages was the ability to access the documents muchmore quickly than previously. Indexes allowed researchers and archivists to findthe records they needed and see them almost immediately. The placement of aretrieval station connected by communication lines in the Tennessee StateArchives also allowed the collection to be accessed by users at a considerabledistance from the actual documents. The image enhancement also enabledformerly low contrast documents to become more legible, although the amountof legibility still depended on the state ofthe original: despite the advancedtechnology offered by digital imaging, good images still cannot be made fromvery poor originals. Reduced handling ofthe delicate and fragile documents alsoaided in slowing down the deterioration of these documents, and helped preventthe deterioration ofthe more stable records as well. Storing the records onoptical disk also allowed for a virtually unlimited number of exact copy prints tobe made without any deterioration of the original document, as would be the casewith photocopies made from the original records. Lastly, the experiment proved15W.L. Hooton et al, Optical Digital Image Storage System Project Report(Final Report), NARAIT1P-90/10 (Washington, D.C.: NARA, 1991),p.9-12.16Holmes, “The ODISS Project”,p.238.87that the amount of space saved by storing records on optical disks would beconsiderable.The ODISS Project also discovered some disadvantages towholesale conversion from paper to optical media. For one, the cost for such alarge conversion is considerable, and only the largest institutions would likely beable to afford such an undertaking as not only the cost ofthe system and the timemust be considered, but also the cost of training the people to operate andmaintain the system. Secondly, optical media, like any machine-readable media,are not “archival” as the technology needed to read the material stored on theoptical media will become obsolete within 10-20 years. While the opticalmedium itself may last as long as microfilm, the systems needed to access themwill not, thus rendering the information stored on the disks or tape inaccessible.The ArchiVISTA system used by the National Archives ofCanada(NAC) also successfully implemented a document imaging project using the20,000 editorial cartoons and caricatures exhibited at the Canadian Centre forCaricature. The ArchiVISTA system was meant to provide “online visual accessto a visual catalogue” of the collection, and allows researchers and the generalpublic a new way to access documentary art and photography collections.’7In 1987 it was detennined that the high-use caricature collectionhad begun to deteriorate to the point that it required immediate action to preventthe records from deteriorating further. Greg Hill, the conservator ofthecollection, recommended that the records be copied onto some “easily accessiblemedium for research purposes to minimize their handling”.18 Based on theresults ofprevious pilot projects involving videodiscs in the late 1970s and early17G. Stone and P. Sylvain, “ArchiVISTA:A New Horizon in ProvidingAccess to Visual Records of the National Archives of Canada”, Library Trends,38:4 (Spring 1990), p. 737.18Ibid.,p.739.881980s, NAC decided in 1988 to employ an optical storage media system utilizingan “80386-based IBM AT compatible microcomputer with a VISTAvideoprocessor board, VGA controller, 19” 1024 x 768 image monitor, 14” datamonitor and Laser drive 810 5.25” digital WORM optical disk drive.”’9The original drawings were prepared for scanning by placing theminto size and artist groupings prior to being scanned. This eliminated the need toreadjust the scanner manually for each scan and assured continuity andauthenticity regarding “image characteristics as a result of an artist’s style and useof materials”.20 As with the ODISS system, the scanned images were presentedon a monitor as they were being scanned, thus providing the scanner operatorwith the opportunity to adjust the image quality immediately, if needed, and thenrescan the image. For each image the operator entered the following information:accession and item number, operator’s name and scan date. The accession anditem number were then linked to the corresponding record description held in theNAC’s MINISIS database, and were also displayed on the upper right side of theimage. The system also automatically gave each image a “frame tag number aswell as the number and side of the optical disk” used.21The ArchiVISTA system, however, only used the WORM disksfor storage purposes, preferring videodisk technology for display and printingpurposes. Each digital image was divided into “four NTSC video frames using avideoprocessor board and storing these, along with an overall frame oftheoriginal drawing, onto 1” “C” type videotape for mastering onto 12”videodisk.”22 The image was retrieved by recombining the four frames into onesingle high-resolution image.19Ibid., p. 743.20Ibid.,p.743.21Ibid., p. 745.22Ibid.,p.747.89The database system used with the ArchiVISTA system was ZIM,a “fourth-generation language product ofZanthe Information Inc.” ZIMprovided a bilingual user interface, Boolean searching and “the ability to enterdescriptive records composed ofvariable length and repeat fields either directlyor through file transfers from M1NISIS.”23The database system also had asearch screen which allowed the user to both browse and/or specilj searchesusing subject, artist, publication, place, date or other unique item numbers assearch fields. It takes the system seven seconds to retrieve an item, but NAChopes to improve the search time. The entire collection of 20,000 images can bestored on two sides ofa 12” videodisk, or approximately 30 5.25” WORMs.The ArchiVISTA system has many of the same advantages anddisadvantages as the ODISS project. One one hand, the equipment needed forsuch a project is expensive, time consuming, and ultimately, the optical disksused to store the images are not considered “archival”. On the other hand, theArchiVISTA system has the advantage of copying a relatively small number ofimages in comparison to the ODISS project, thus making the process simpler andfaster to complete. All considered, the ArchiVISTA project has proven its worthby allowing researchers and staff to perform searches much faster and withoutcontributing to the deterioration of the cartoons and caricatures.IMPLICATIONSOne of the primary implications ofboth the ODISS andArchiVISTA projects is that the transferring of text or images onto opticalstorage media is possible, and depending on the budget available, can be done onvarying scales. Both projects also showed that standard microfilm procedures23Ibid.,p.747.90could be used to scan the records and maintain the same integrity ofthedocument as is presently achieved with microfilming. The use of a LANconnection in the ODISS Project highlighted the possibility of increased access torecords and of general dissemination of information regarding both the scannedrecords and the rest ofthe institutions’ holdings. The image enhancementcapabilities ofthe two systems also demonstrated the way optically storedrecords could be made more readable without causing any deterioration to theoriginal. Conservation and preservation of the records was also enhanced by thesystems’ ability to generate copies or prints from the scanned records rather thanthe originals. Although neither project involved the migration of electronicrecords to optical disk, that too is a possibility for the conservation of machine-readable records.Unfortunately, the optical storage systems used by NARA andNAC are expensive in terms of money, time and skills needed to run and maintainthe systems. Although there are smaller optical storage media systems comingout on the market today, they still represent a fair investment for any archives.Again, any archives considering the implementation of an optical storage systemmust take into consideration the problems of system obsolescence, the legalissues presented by records scanned onto optical media, copyright legislationregarding the transmission of records via networks, and the lack ofindustry-widestandards for the production and recording of optical storage media. While theexamples shown in this chapter involve national archives, similar techniquescould easily be applied in other settings.91CONCLUSIONOptical storage systems have advantages and disadvantages aspractical solutions to archival storage, conservation, preservation and informationneeds. The advantages have the potential to revolutionize the way archivalinformation is accessed and stored. The disadvantages have the power to createhavoc in any archives. Consequently, archivists must obtain a basic knowledgeofthe types of systems available on the market, the methods of preservation andconservation of optical media, and the ways in which these media can serve asrecords conservation, preservation, storage and access tools.ADVANTAGESOne ofthe main advantages of optical disk systems is their abilityto store vast amounts of information in a physically small amountof space. Asseen with the ODISS Project, a warehouse of information can be contained on arelatively small number of disks, or Optical Tape. The stored data are then easyto manipulate, compare and analyse, and if on WORMs or Optical Tape, they arepermanently affixed. Jukeboxes can be used toform a large database, andincrease even further the potential uses ofinformation stored in thismanner.Local Area Networks (LANs), such as theone used in the ODISS Project,facilitate the dissemination of data and findingaids, thus increasing the records’accessibility to researchers. Copyrightownership of both the system softwareand material stored on the disks must be taken into consideration,however, aswould possible restrictions on accessibility tothe documents. The archives woulddisseminate only the data to which it had clear copyright,and limit access to92restricted records or those records to which the archives did not have copyrightprivileges.Processing and retrieving information is also easier with recordsstored on optical storage systems. For instance, the problems associated withmanually misfihing documents and paper file maintenance would be eliminated.Optical media are immune to most environmental hazards, and thus theinformation stored on them is much more difficult to destroy or damage than thatstored on paper or magnetic tape. Capturing documents is also simpler, as theycan be scanned and placed within the system immediately, with savings to bothprocessing and retrieval times.Optical storage media also have the capacity to act as multi-mediastorage devices, as text, graphics, video and sound recordings can be supportedby this technology. This capability would allow multi-media fonds to be kepttogether on disk, thus maintaining their integrity and original order even iftheoriginals would have to be physically separated for conservation purposes.Finding aids for such fonds would also assist researchers, as all the necessaryinformation about the fonds would be centralised, rather than in separate media-based finding aids. Moreover, archivists would be able to access fonds andrelated information from areas outside their own particular administrativedivisions, and different divisions would have simultaneous control of all therepository’s holdings.The convenience of placing data on optical storage systems,however, could lead to lower standards of appraisal. A solution to this might beto use MO disks, an erasable form of optical disk, as an interim storage medium.MO disks could be used to store short-term documents, documents which are inprocess and not yet in their final form, or to temporarily store documents beforethey are transferred to non-eraseable media, that is before a definitive appraisal93could be made. While this may sound like the ideal solution, MO disks areplagued with the same lack of standards and unproven lasting ability as non-erasable optical media and present similar problems to archivists and recordsmanagers alike.DISADVANTAGESThere are also several disadvantages to using optical mediasystems for archival storage. The main drawback is the lack of industry-widestandards for producing the systems used to write or access optical media. Atthe present time, there aren’t any standards for formatting information onto disksor tape, for interfacing with other optical media or hard drive systems, or for thehardware needed to use the optical media themselves. As a result, it isimpossible to mix and match optical storage systems or the soft and hardwareneeded to run them. Some WORM systems are so proprietary, that some read apit as a zero, and others as a one.’ This lack of compatible hardware andsoftware, or any standard production or writing formats, can create problems forarchives as they would either have to maintain a large amount of optical storagesystems to ensure future access to the data encoded on the disks or institute aprogram of regular migration of incoming electronic records to more stableformats.This lack of standards and a stable technology create problems toarchivists who might receive transfers of large amounts of outdated,unsupportable, obsolete optical storage systems. Life expectancy of up to 100years notwithstanding, changes in technology easily make optical storage systemsobsolete and the information stored in them inaccessible long before the disks or1D. Harvey, “State of the Media”,15:12 (November 1990),p.280.94tapes are transferred to the archives.CONSEOUENCES FOR THE ROLE OF THE ARCHIVISTThe presence of optical media records in an archives will affect thearchivists’ role, but only to the same extent as have other technologicaldevelopments. Optical media are machine-readable storage devices, as aremagnetic tape and floppy disks. The traditional archival functions of appraisal,arrangement and description, conservation and reference will still have to be doneaccording to the same principles and methodologies, regardless of any advancesin technology or on what on media the records exist. Appraisal will have to takeinto consideration both the contextual and technical components ofthe records,as always. Arrangement, for instance, will have to keep into account thelocational indexes as they could be indicators to the original order of therecords.2 Description will have to take into consideration technical descriptionof the hardware and software systems used, and the practicalities of obtainingphysical access to the records. Conservation will have to follow the developmentof new technology and rely on the future generations of optical media and opticalmedia-related systems. Despite the potential user friendliness of optical media-based multi-media integrative finding aids, reference archivists will still be neededto help researchers navigate their way through the records. Optical storagesystems will have an impact on the way documents are handled within thearchival context, but the best technological advantages will not be a substitute fortraditional archival work. 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