An ABC News Australia article calls attention to the problem of archives on magnetic tape. Author James Elton clearly knows something about digital preservation issues, as the article goes beyond the usual generalities and hand-wringing.
Tapes, on the other hand, can only be read by format-specific machines.
And dozens of formats of magnetic tape were created through the last century — one-inch, two-inch, various versions of Betamax.
The machines to read many of those formats just aren’t being made anymore. It’s still possible to get a Betamax player; with some formats, even finding a used one that still works is nearly impossible. The most critical component is the tape head, which has a finite life. The article quotes a figure of 5,500 hours. If a machine is running continuously 40 hours a week, that’s less than three years.
The history of digital tape
Magnetic computer tape is nearly as old as the electronic computer. The Univac computer used magnetic tape as its primary long-term storage device in 1951. It was much faster and more compact than the punched cards that earlier computers used. IBM announced its own 726 tape drive the next year.
The Univac tapes had eight channels, including one for parity and one for timing. The IBM tapes had seven channels, without a timing channel. Univac tapes held 128 bits per inch, and IBM tapes held 100 bits per inch. This was the beginning of a long history of incompatibility. Manufacturers sold drives for their own computers, and horizontal markets for peripherals didn’t exist then.
Since then, there hasn’t been a lot of improvement. Reel-to-reel magnetic tape has never settled down on a standard. It isn’t just that each manufacturer had its own standard; important details of the recording method have changed from one model to the next.
Apart from reel-to-reel, a variety of digital tape cartridges and cassettes have come and gone over the years. Sony introduced Digital Audio Tape (DAT) in 1987 and finally gave it up in 2005. It was originally conceived as an audio storage medium but saw more use for data storage.
Digital Equipment Corporation introduced DECtape in 1964. It used laminated tape on 4-inch reels. The drive could move forward or backward to access specific data locations, giving it a quasi-random access character.
In the early days of hobby computers, audio cassettes were a popular, inexpensive data storage medium. The computer encoded bits as audio frequencies. It was unreliable and didn’t store a lot, but in those days everyone had a cassette deck.
One example of tape obsolescence is the story of LTO tape for archiving motion pictures. Toward the end of the 20th century, movie makers began using it to create digital archives. Even the first generation could hold 100 gigabytes in a single cartridge. Since then the capacity has climbed into the multi-terabyte range. Unfortunately, the newest machines don’t support all the older versions. Film archives have to migrate their older tapes or lose access to them.
Where is tape going?
Magnetic tape still has its uses. It’s hard to beat for storage density. Like any magnetic medium, it will degrade over time, but it will last for decades if stored properly. It’s slow and can’t easily find specific items, but that’s not so important for archival storage.
The problem is drive compatibility. When you store data on tape, you have to hope the drive’s manufacturer will continue to support it. If it stops, you’re at a dead end. Because tape can hold so much, it’s hard to copy a large set of reels onto other media.
It’s a kind of devil’s bargain. Tape lets you hold more data than anything else does. But if you ever fall behind, you can lose everything.