In his column on Do CDs have a life expectancy of 10 years? from 2002, Cecil writes,
Consider a storage medium considered cutting edge 50 years ago–magnetic tape. It’s now recognized that tape degrades after 20 years, maybe sooner, unless you’re extremely careful. Some tapes used for the 1960 U.S. census became unreadable and the data was almost lost. (Luckily they had a backup on microfilm, which supposedly will last 500 years, although even microfilm has doubters.)
That’s not quite the story. The magnetic tapes contained microaggregate data, not the raw data, from the 1960 U.S. Census. And only 0.2% of that microaggregate data was lost due to deterioration of the tapes. From the Center for Electronic Records, at the National Archives :
All of the aprochyrphal stories about loss of 1960 Census data have to do with the 1960 derivative data that the Bureau stored on tapes readable only by UNIVAC II-A tape drives, II-A (or, 2A) tapes. During 1975 and 1976, a member of the National Archives’ Machine Readable Archives Division reviewed the microaggregation or derivative files that the Bureau of the Census had preserved from the 1960 Census on these II-A tapes. This review identified seven series of low-level microaggregations as having long-term value to compensate for the lack of basic microdata records from the 100 percent Census. The seven series resided on 642 of the II-A tapes which the Census Bureau agreed to migrate to [industry] compatible tapes. But by this time, the Univac II-A tape drives were obsolete, and thus the preservation of these tapes presented a major engineering challenge. Despite the challenge, the Census staff prevailed. By 1979, the Census Bureau had successfully completed the copying of 640 of the 642 II-A tapes onto 178 [industry] compatible tapes. The two II-A tapes not copied could not be found. The missing tapes had 7,488 records, or about .5 percent of the total of approximately 1.5 million records on all II-A tapes that had been identified as having long-term value. Of the 640 tapes which were located, only 1,575 records (or less than .2 percent of the total number of valuable records on II-A tapes) could not be copied because of deterioration. Hence a small volume of records from the 1960 Census was lost, and this occurred because of inadequate inventory control and because of the physical deterioration of a minuscule number of records.
What a relief! Finally, I can sleep at night.
I suspect that with today’s technology they could actually read those two tapes.
That is, even in 1979 tape bits could be made visible to the naked eye by “developing” them with chemicals as though they were photo film. These were frequently passed around in tech schools so students had some clue what the physical basis was.
I don’t know about that. I believe IBM was up to 6250 bits per inch by then.
They could have read them with 1975 technology, too – except:
If they can’t be found, I don’t think any year’s technology will be able to read them.
Time travel?
Hmmm. Maybe that’s why they can’t be found. They shoulda left a memo.
kayT
April 2, 2008, 10:00pm
8
Is it really the case that the Center for Electronic Records at the National Archives cannot spell apocryphal?