recovering cartridge tapes (was: Tek fiches found! (was: Looking
ard at p850ug1.demon.co.uk
Fri Jul 23 13:28:17 CDT 2010
> > IRIC the Tekky 405x series didn't use any of the standard encodings,
> > though. They had a 2 coil head that read/wrote 2 tracks at the same time.
> > A pulse on one track was a '0' bit,a pusle on the other track was a '1'.
> > Whether simultaneous pulses on both tracks were used as some kind of
> > marker I don;t know, many otehr similar systems did use that.
> It was indeed. Pulse on one track = 1, pulse on other track = 0, pulse
> on both tracks = marker. The pulses on each track were alternately
> positive- and negative-going to minimise the dc component.
That makes sense. I should probably have said 'flux transition' rather
FWIW, the HP9830 'calculator' uses a similar encoding scheme on compact
cassettes (driven by the spools only, there is no capstan and pinch
roller, but since this is a self-clocking scheme, it doesn't matter that
the tape speed isn't consant). The HP9865 cassette drive and I assume the
HP9821 do the same thing.
As do the handheld calcualtor magnetic card readers
(HP65/HP67/HP97/HP41). The desktop magneitc card systems
(HP9100/9810/9820) do not, though.
> I have the spec somewhere. Probably in one of my Tek service manuals.
How detailed a spec? Is there enough to understand the cotnents of a tape
at the file level?
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