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
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
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
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
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.
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 . . . .
|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).
|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
|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
If you don't hear the sounds, the
computer audio input could be faulty - do you have
another computer to try?
|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
recognised, but won't load successfully
|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.
|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
Depending on the degree of contamination, more
forceful action may be required - try cleaning the
head using a cotton bud and isopropyl alcohol.
|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.
|As above, the playback settings can be different
for different tapes, experiment with various Volume
and Tone (where available) settings
|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.
|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.