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[Ron Thigpen <rthigpen AT nc.rr.com>]

Gina Norman wrote:
> Each cassette tape had some capacity to hold data -- just like a CD-R can
> hold 650MB, a cassette could hold _some_ amount.
>
> What was that amount?  (Assuming I mean a 45 mins./side cassette).

Those cassette tapes weren't being used to store digital data, at least 
in native form.

Remember how you hooked up that device?  It was a connection to the 
microphone input!  I know you must have gotten curious and listened to 
one of those tapes.  They had a kind of high-pitched, warbly howl to 
them.  Remind you of anything?

Yep, between the cassette recorder and the computer there was a *modem*, 
modulating for recording, demodulating for playback.  Depending on the 
time period we're talking about, state of the art for modems would have 
been somewhere 300 and 1200 baud.  There'd be limitations on recording 
and playback due to the medium, as well.  Pre chromium dioxide and Dolby 
B, cassette tapes didn't do very well with high frequencies, and were 
also very noisy.

(standard disclaimer for likelihood of bad math...)

Optimistically assuming 300 baud
stored bits ~= (300 bits/sec * 60 sec/min * 45 min) = 810,000
in kilobits = 810,000/1,024 ~= 791 kb
in kilobytes = 791/8 = 98 kB

I'd guess these device were actually doing maybe a half to a third of 
that.  I remember waiting for what seemed like the better part of an 
hour for my small BASIC programs to load and record.  But, hey, it beat 
the crap out of re-keying every time and I was damn glad to have it.

Converting to mp3 filesize terms, at 128kbps recording rate:

791 kb/128kbps ~= 6.18 seconds

Even if you were getting 1200 baud and used both sides of a 90 minute 
tape, you'd still only be able to store about 50 seconds.

Quod erat demonstrandum, analog is king.

--rt