Cassette Tape Data Storage

At the start of the home computer market in the early '80s, mass storage was an expensive option - even floppy disk drives and media were not economically viable for a "home" computer. The majority of systems at the time used cassette tapes for offline, "mass", storage. This was a time when most households would have had a cassette tape recorder/player for use with their music centre - remember, home taping was killing music back then :-), and the medium was an obvious choice for software distribution and off-line data storage.

Typically a home computer would generate audio tones to encode data, that could be stored on audio tape through a direct connection to the recorder. (There is an interesting article on how data for the ZXSpectrum was encoded here, the MTX would have used a similar technique). Re-loading the data required re-winding the tape. The home computer would contain some circuits such as a phase-locked loop to convert audio tones back into digital data. Since most consumer cassette recorders were not made for remote control, the user would have to manually operate the recorder in response to prompts from the computer screen.

Apart from the low speed (typically <2400bps), the biggest disadvantage of this medium was that it did not allow random access to the data on the tape, the entire tape would have to be searched to retrieve any particular item. This was not a problem when loading commercial software where a single program was normally supplied on a tape but when loading / saving multiple user programs on a single tape things were more difficult. One method was to use the tape counter on some recorders to record when given programs started and ended then use the Fast Forward and Reverse functions of the tape recorder to position the tape to the required point.

Compact Cassette tapes came in a variety of capacities - usually rated by the length of playing time on an audio recorder/player. Typical audio capacities were C60 (30 minutes per side), C90 and C120. As the tape capacity, and hence length increased, the tape needed to be made thinner to fit within the tape enclosure - this made the longer tapes more prone to stretching or breaking. Cassettes marketed as computer data tapes were smaller, C15 being a typical size.

Tape Loading Problems?

Original tapes from home computers of the mid '80s are now around 30 years old. Depending on how and where they have been stored, some degradation is to be expected, I imagine that many were consigned to lofts and storage cupboards a long time ago and exposed to fairly large temperature and humidity variation over the period.

Consequently, some tapes may be unreadable - assuming that you even have a cassette tape player - portable cassette players are themselves something of a rarity these days, probably most of the cassette players still around are part of hi-fi systems, these are of course, still suitable for loading tapes into home computers of the period, provided that the tapes are still readable. If available though, an old mono cassette player is likely to be better for home computer use.

Even where tapes are still "good", loading of them can be a bit "hit and miss", in the event of difficulty in getting a tape, or tapes, to load, some reminders from the time might help . . . . .