Subject: RE: Preserving ancient media

From: "Hills, Paul" <[email-masked]>
Date: Wed May 21 10:18:24 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: [email-masked] [mailto:[email-masked]]
Sent: 20 May 2003 00:26
To: [email-masked]
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

---

From: [email-masked] (Tony Duell)
Date: Sat May 24 19:16:43 2003

> is not too much of a problem.

Do just check that you can expand this back to a WAV file (shouldn't be a 
proble, zip is not a lossy compression method) and that you can replay 
the WAV file into the computer concerned. No point in archiving data if 
it can't be used...

> some of those computers!.

Indeed...

-tony