> ... and that reason is ? A little less tersely please ;-)
As someone has mentioned it is limited to one bit in mono (it didn't occur
to me that you could use both channels). It has to cope with all kinds of
tape recorders of different qualities (and often your cheapo mono cassette
recorder would fare better than your expensive stereo).
Someone else has mentioned that you could increase the speed to 4500 fairly
reliably. My experience has been that with a good tape recorder this would
work at the time, but if I tried to load the tape a couple of months later
the system wouldn't even recognise the header. I imagine the speed of 1500
was chosen because it was the best that could be guaranteed to be reliable
under a wide range of conditions. Later on some games were supplied with
loaders which worked at 1.5 to 2 times the speed, but the manufacturers at
least had control over half the process (that is, they could record it using
high quality equipment).
There are all sorts of things you have to contend with on tape which
don't occur with modems. Firstly there is degredation of the recording,
stretching of the tape, print-through, etc. Secondly there is the fact that
you can't guarantee the quality of the tape recorder. To be conservative
you shouldn't rely on a response of much more than 10kHz. Also, if your
tape recorder breaks down and you play the tape back on a different machine,
how will the quality of the playback differ? There is also the fact that
tape players have volume and tone controls which can be fiddled with and
you want to make it as easy as possible to find settings which work.
Thirdly, if a dropout occurs on a phone line then you can just ask the
sender to repeat the last packet; this is impossible with tape devices.
imc
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