recovering cartridge tapes (was: Tek fiches found! (was: Looking

[Tony Duell]

> 
> > 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 
than 'pulse'.

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?

-tony