Preserving ancient media

From: Hills, Paul <Paul.HILLS_at_landisgyr.com>
Date: Wed May 21 09:51:36 2003

Thanks for that.

I tried simply zipping up a .WAV file created by the program I mentioned and
it compressed from 544kb down to 3.4kb. The original data file was 409
bytes, so although the result is 8 times bigger than the data file, storage
is not too much of a problem.

At this compression ratio (or rather expansion I suppose), a CD could store
80Mb of original computer data - more than was probably ever written for
some of those computers!.

paul

-----Original Message-----
From: ard_at_p850ug1.demon.co.uk [mailto:ard_at_p850ug1.demon.co.uk]
Sent: 20 May 2003 00:26
To: cctalk_at_classiccmp.org
Subject: Re: Preserving ancient media


> That's sort of what I was thinking of. Of course, as you say, it is ZX81
> specific.
>
> Were these home computer tape format's standardised in any way, or at
least

Not at _all_ Just about every manufacturer did it his own way...

> based on an older standard? I seem to remember a format called
> "Cottis-Blandford" from years ago. Am I right in saying that most home

I thought the common one was 'Kansas City', but that was not common on UK
home computers (the BBC micro was perhaps the closest to it).

> computer's tape data format was 1200Hz and 2400Hz for logic 0 and 1 (maybe

No! Some did, many didn't.

What's worse is that some manufacturers used a constant time for each bit
(so that one state was a single cycle of 1200 Hz, the other was 2 cycles
of 2400 Hz, say), but many other manufacturers used a single cycle at
each frequency for the 2 states. This means the bit rate is not even
constant...

> the other way round). How many stop/start & parity bits (and possibly more
> control bits) are sent may be computer-specific I guess.

However, a reasonable quality digital audio recording of these old tapes
might well be enough to preserver them (you could play it back to a real
tape, or directly into the home computer). It's not an efficient way to
store the data, but it's better than losing it totally.

-tony
Received on Wed May 21 2003 - 09:51:36 BST