Re: IIe tape drive

[mjmahon@aol.com (Michael J. Mahon)]

Anonymous Coward asked:

>Are there any old computers that did use stereo?  was the data ever
>different on the left channel than the right?  that would have been an
>interesting way to achieve storage "compression".

No.  Stereo would have required two channels of audio I/O, and since
cassette I/O was handled with timing loops by the CPU, it would have
been very tricky to decode the two channels simultaneously.  The timing
skew between the channels would be many tens of microseconds, and
varying as the tape stretched and its path meandered around.

Speed was never the driver for cassette I/O--cost and relaibility were the
fundamental requirements.  (And many users never achieved the level
of reliability required for confidence.)  Doubling the hardware requirements
and complicating the decoding software, just to benefit those who had a
stereo cassette deck, would have been a poor cost-benefit tradeoff.

As a side note, many users who were able to use cassettes relaibly
on their own systems found that they could not reliably exchange
cassettes with other users.  In my experience, the most significant
factor in this situation is relatively poor head alignment on inexpensive
cassette recorders.  Any misalignment of the playback deck's head
azimuth relative to the recording deck results in loss of high frequencies,
and the data values are contained in the timing of the edges, which are
degraded by high-frequency loss.  As a result, users should either:
1. don't interchange cassettes--always reading a cassette on the
recorder on which it was written (this bypasses the alignment problem),
or 2. before using a recorder, adjust its alignment carefully with a
standard alignment tape (hard to find) or, possibly, with a good brand
pre-recorded music cassette with clear high frequencies.

If you adjust your alignment after recording some cassettes, you may
find that you have rendered them unreadable, since the reading head
azimuth no longer matches the writing azimugh.


-michael

 Email:  mjmahon@aol.com
 Home page:  http://members.aol.com/MJMahon/