Re: NEWSFLASH! Linux ported to Commodore VIC-20!!

H. Peter Anvin (hpa@transmeta.com)
14 Sep 1998 19:36:25 GMT

Followup to: <m0zIbdN-000aQwC@the-village.bc.nu>
By author: alan@lxorguk.ukuu.org.uk (Alan Cox)
In newsgroup: linux.dev.kernel
>
> > Hmm, quickndirty calc for 90 minute tape at 64kbits =40megs or so. If
> > you can only get 32kbits then you still get 20megs... The sound
> > engineers among us can no doubt confirm bandwidth and S/N issues, but I
> > would have thought that at least 32kbits would be doable with a little
> > error correction ?
>
> 8bit micro people never got about about 3000bits/second off old cassette
> tape (MFM or FM encoded). Its just horrible stuff for distortion and
> stretching
>

MFM is also pretty crappy encoding when you're limited by bandwidth
rather than dynamic range. Tape is better than the phone lines in
many ways, although distortion is a problem; linear stretching appears
as a slow drift of the master clock and shouldn't be a significant
problem if you keep it in mind while writing the decode algorithm,

Furthermore, 8bit micros *never* used any form of ECC, usually a
16-bit CRC or checksum over the blocks was all that was ever used.

With QAM or Trellis, I wouldn't be surprised if you could get 16-32
kbps with a decent audio deck.

-hpa

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