Computers Overview
Commodore PET
Sinclair ZX80
Sinclair ZX81
BBC Micro
Commodore 64
Sinclair ZXSpectrum
Memotech MTX
Memotech CP/M
Atari ST
Commodore Amiga
DEC 3000 AXP
Raspberry Pi



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 . . . . .

Problems loading any tapes

Tape not being recognised by the computer

After the tape "lead-in", if the computer recognises the tape, you should see a message such as FOUND "Program Name" displayed on the TV/monitor. If not, check the following . . . .

Connections Obvious, but double check that the connections between the tape player and the computer are correct, e.g., "Ear" to "Ear" (computer input) and "Mic" to "Mic" (computer output). (The "Mic" connections are not needed just for loading tapes).
Player Again obvious, but check that your player is actually producing audible output, without the "Ear" cable connected to the player, you can expect to hear the recording start with a high pitched tone of a couple of seconds followed by the familiar "screeching" and "warbling" sounds through the player's speaker as the tape plays.

If you can't get this far :

  • the cassette playback is faulty
  • or the tape is blank  
Computer With the "Ear" cable connected, sound enabled and the volume turned up on the TV/monitor, you should hear the tones through the TV/monitor as the tape plays.

If you don't hear the sounds, the computer audio input could be faulty - do you have another computer to try?

Cable It is unlikely, but not unheard of, that the original cassette cable for the computer may be damaged, try using a cable which has been proven to be good.
Tapes being recognised, but won't load successfully
Playback settings Probably the most common cause of loading problems. Successful loading can be very sensitive to the Volume and Tone (where available) settings on the cassette player. Experiment with various settings, with my equipment, I find that a volume setting of around 90% (I have no tone adjustment) seems to work best.
Tape Head Make sure that the tape player's heads are clean - normal usage will result in some deposition of the magnetic oxide from tapes onto the tape head. Make sure that the heads are clean, you may have a tape head cleaner - a compact cassette containing a slightly abrasive tape designed to remove such depositions.

Depending on the degree of contamination, more forceful action may be required - try cleaning the head using a cotton bud and isopropyl alcohol.

Player If possible, try another cassette player

Problems loading a single tape

Are you sure? Make sure that it is not a problem common to other tapes and that you can successfully load other tapes into the computer, if not, see above.
Playback settings As above, the playback settings can be different for different tapes, experiment with various Volume and Tone (where available) settings
Change sides Most commercial software was distributed with the program recorded on both sides of the tape. If one side does not work reliably, try loading the copy on the reverse side of the tape.
Player If possible, try another cassette player, it is just possible that you may be able to load the tape successfully using another player.

If not, it is pretty likely that the tape has degraded to a point where it cannot be read and you will, unfortunately, have to find an alternative. 


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