Before getting up steam for this article, I contacted a former colleague who worked for several decades on the editorial side of the consumer-audio press. He became one of the first collectors of Compact Discs, a medium trusted by many archivists. The oldest items in his collection date back to the original Q4 1982 launch of audio CDs. Were the oldest discs still playable? “Yes,” he replied, “but, if you are writing on the subject, be sure to mention filiform corrosion which was a problem in the very early years."
Filiform corrosion, less elegantly known in this context as ‘CD rot’, turned out to be a phenomenon familiar to many motorists: rust. It occurs under a damaged or discontinuous protective film, especially lacquer or quick-dry paint. Early CDs, it appears, were prone to moisture ingress at the inner and outer edges. Since a CD is essentially a sandwich of transparent polycarbonate, reflective-metal, lacquer and printed label, the potential for oxidisation existed for several years until manufacturers took the trouble to seal the edges.
My own commercially-recorded audio CDs date back to 1995 and are all still perfectly playable. The only degradation noticed has been of the thin plastic foam included in multi-CD sets to prevent adjacent discs scuffing each other; the foam disintegrates. Most TV-Bay readers will have had the occasional bad experience with locally burnt CDRs and DVDs but those effects are usually noticeable as soon as the copy is checked.
The Dutch facilities company Nederlands Omroepproduktie Bedrijf went into archiving legend in the early 1980s when a zealous librarian decided to write ‘NOB’ on the label of every CD in its archive to discourage unauthorised removal. Unfortunately the ink in the pen employed reacted with both the CD lacquer and the metallic data surface, rendering every disc unplayable. This unlikely-sounding story was later confirmed to me by one of NOB’s senior managers.
Optical data storage on CD and DVD are today commonplace wherever data is archived. The weakness both of CDs and DVDs is their susceptibility to scratching, not from the ‘read’ side where you might expect it but from the label side. The optical beam reading a CD or DVD is always focused through the polycarbonate to the active data layer. Isolated scratches on the transparent surface of the disc therefore cause little harm to the transfer of optical data. Multiple scratches within a small area, also multiple dropouts within a close region of the metallic data carrier, are more likely cause a problem.
Many independent video and audio content producers today put their faith in an older and simpler technology than optical discs: rigid magnetic disc drives, casually termed 'hard drives'. The stand-alone variety are cheap, robust and can be shelf-stored as easily as tapes, ideally together with their power brick. Most drives come with a three-year guarantee covering the motor, the ultra-fragile write/read head and the supporting electronics. Buyers get to choose between a fairly tough USB in/out connector or a very fragile-looking miniature equivalent, with the newly emerging option of a Thunderbolt connector which, in terms of robustness, looks half way between the two.
A three-year media guarantee may be respectable in the fast-developing computer world but it is very short for an archivist. And how secure are the magnetic impulses? Some of the oldest magnetic recordings known are the reversals in Earth’s polarity captured over millions of years at gradually widening splits in the planet's crust, for example the mid-Atlantic. The magnetic domains involved are very large. Those used for data storage are sub-microscopic so inherently more likely to fade even if captured in a very high-remanence carrier.
Most broadcasters, along with an increasing number of production houses, today ingest as much as possible of their creative content to networked magnetic disc drives which can be accessed from any connected computer. This arrangement eliminates the wear and tear otherwise imposed on discrete media such as video tapes and reduces the danger of loss during delivery. Networked drives also allow any item to be delivered to, or browsed from, several locations at the same time.
Supporting the networked disc drives is commonly a library of magnetic tape cassettes or cartridges with a robotic loading mechanism to move the tapes from shelf to tape deck and back again. Since its introduction in 2000, the popular Linear Tape Open cartridge has evolved from 100 gigabyte-native LTO-1 to 1.5 terabyte-native LTO-5. Plans already exist for high-capacity LTO-6, LTO-7 and LTO-8. Future archivists will need very flexible technology to cope with this inheritance, let alone a legacy of 2 inch, 1 inch, three-quarter-inch, half-inch and quarter-inch video tapes, some of which may still be just about readable if the appropriate machinery can be found (or, more likely, 3D-printed).
The dangerous reality of modern broadcast archiving is that anything stored magnetically, and that obviously includes LTO, is susceptible to magnetic fade. Even if the supporting medium survives intact, the micro-magnetic waveform is subject to gradual randomisation. Analogue audio and video recordings gradually lose their energy, particularly at short wavelengths, though rarely tumble over the ‘digital cliff’ of becoming unplayable. About 1990, I bought a Yamaha SY77 music synthesizer and began inflicting malodorous melodies on anyone who came within listening distance. The SY77 captured MIDI tracks and voice-configurations to 3.5 inch diskettes of the kind used on contemporary personal computers. A few years on, I archived the resultant audio tracks as WAV files on CD. Just as well. The original diskette files gradually faded and became almost entirely unplayable.
Magnetically-recorded data can obviously be safeguarded by recopying at regular intervals. Unlike analogue copying which causes an inevitable loss of quality, each digital pulse is reconstructed to effectively ‘as new’ condition. The same applies to robotic-library tapes but here the additional question of media wear has to be considered. Thin tape is inherently fragile though accidents during lace-up are rare, particularly in linear (as distinct from helical scan) formats. Editing helical-scan video tape was never mechanically very kind to the tape surface but most video editing is now performed on disk with the write/read head separated from the magnetic medium by an air-gap so mechanical wear is almost a non-issue.
An archiving strategy already common among large-scale computer users involves the use of third-party data storage agencies. Many broadcasters have taken this a stage further by subcontracting their playout activity as well as their archiving to specialist service providers. Playout is a competitive market, including companies such as Advanced Broadcast Services, Arqiva, Ascent Media, Globecast, Playout247, Red Bee Media, Technicolor, Viasat and WRN Broadcast. Even the archives held by these organisations, however, should be regarded as supplementary to a programme producer’s or rights-holder’s archive rather than as a substitute for it.
Many broadcasters maintain some kind of disaster recovery centre to ensure continued operation in circumstances such as local flooding, technical outage or civil unrest. The accepted wisdom among archivists is that nothing is safe unless it is held at three or more separate locations.
Human factors are the most common cause of data loss, either through accidental file deletion or failure to anticipate future demand for content deemed not worth keeping. Data storage devices and services have become steadily more affordable with the passage of time and look set to continue on that path until such time as new memory technologies supercede existing technology.
Unless you are in politics, the safest archiving policy can be summed up by just two words: Delete nothing.