Diskette size

Paul Koning paulkoning at comcast.net
Fri Jul 21 14:19:48 CDT 2017

> On Jul 21, 2017, at 2:30 PM, Chuck Guzis via cctalk <cctalk at classiccmp.org> wrote:
> On 07/21/2017 10:37 AM, Adrian Graham via cctalk wrote:
>> I have a Facit9911 2 11/16” (or 70mm in new money) microfloppy drive with a mahoosive interface module which google turns up precisely nothing about. I’m pretty sure I’ve mentioned it here before but even a search of the archive turns up nothing.
>> See pic - http://www.binarydinosaurs.co.uk/facit9911MicroFloppy.jpg
> Even before flexible magnetic disks were used to record digital
> information, they found use in audio equipment.  E.g. the Telefunken DT-600:
> http://vintage-technics.ru/Eng-Telefunken_600.htm

Interesting.  Another example, slightly later, is the audio unit of the PLATO IV terminal (1974 or thereabouts).  It uses a rather large disk, perhaps 10 inches diameter, brown oxide, no grooves.  It's a random access device, with 128 tracks.  Each track has 32 sectors; a given audio clip can be up to 127 sectors long (though I'm not sure what happens if it's more than 32 sectors -- does it switch tracks?  Seems unlikely).

The track seek is done with a binary encoded pneumatic cylinder assembly, 7 cylinders -- low order stroke is one track pitch, next is 2 tracks, next is 4 tracks, etc.  So the binary track number would select 7 air valves which would feed supplied "shop air" to one or the other side of each piston, moving the read/write head to the correct track.

These terminals also had a back-protection setup for the plasma panels (the "slide projector", actually more like a microfiche projector).  Same sort of setup, but with X and Y both done by binary weighted sets of 4 air cylinders each.


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