Confusion and controversy over the expected lifetime of magnetic tape may have begun as the result of an article in the January 1995 Scientific American which cited magnetic tape life expectancy as 1-2 years. The NML refutes this figure. Years of research, industry, and operations support experience at the NML show magnetic tape life expectancy to be 10-30 years.
Dr. John W. C. Van Bogart, prinicpal investigator of media stability studies at the NML, sent the following response to the editor of the Scientific American. Please feel free to comment.John Rennie, Editor in Chief
A Letter to the Editor of the Scientific American:
I am writing in regard to the article, "Ensuring the Longevity of Digital Documents," which appeared in the January 1995 issue of Scientific American. I am the Principal Investigator for the Magnetic Media Stability Program at the National Media Laboratory (NML), an industry resource supporting the U.S. Government in the evaluation of storage media and systems.
My NML colleagues and I agree with the key point made in this article-that the technological obsolescence of digital recording systems is a challenge for those individuals tasked with preserving digital archives. Digital archives should be transcribed every 10 to 20 years to ensure that they will not become technologically obsolete. To realize lifetimes greater than this, one would be required to archive the recording system, system software, operating system, computer hardware, operations manuals, and ample spare parts along with the recorded media.
My main contention is that the author has severely underestimated the physical lifetimes of digital magnetic tape. A chart in the article indicates that the physical lifetimes of magnetic tape are only one to two years. He states "digital magnetic tape should be copied once a year to guarantee that none of the information is lost," and "media with increased longevity are not on the horizon." Both of these statements are grossly inaccurate for current digital tape formats. Experience indicates that physical lifetimes for digital magnetic tape are at least 10 to 20 years, a value commensurate with the practical life of the digital recording technology. One government agency responsible for maintaining meteorological data archives recently transcribed approximately 20,000 ten-year-old 3480 tape cartridges, of which only two cartridges had unrecoverable errors. Properly cared for reel-to-reel, 9-track computer tapes recorded in the 1970's can still be played back in the 90's, even though the 9-track format became obsolescent in the 80's. The NML has investigated the stability of several forms of digital storage media over the last six years. Life expectancies for magnetic media can be estimated by modeling the deterioration of tape properties induced experimentally in accelerated aging environments. Life expectancy estimates of 10 to 30 years for magnetic tapes are common. Given the fact that digital recording technologies can be supplanted by a newer format every 5 to 10 years, the bigger problem facing archivists is the lifetime of the technology, not the lifetime of the medium.
Of course, media life expectancies are like miles per gallon ratings on automobiles-"your actual mileage may vary." They are highly dependent on media storage conditions. In general, a controlled range of storage temperatures and humidities will increase media life expectancies. The National Bureau of Standards publication, Care and Handling of Computer Magnetic Storage Media, recommends that magnetic tape be stored at 65 +/- 3 degrees Fahrenheit and 40% +/- 5% Relative Humidity.
In conclusion, I believe that the author has been unduly pessimistic in his estimation of the physical life of digital magnetic media. Studies by the NML indicate that magnetic media, properly cared for, should have a lifetime which equals or exceeds that of the recording technology (10 to 20 years).
Sincerely,Dr. John W. C. Van Bogart