> On Jul 21, 2017, at 3:42 PM, Fred Cisin via cctalk <cctalk@classiccmp.org>
> wrote:
>
> On Fri, 21 Jul 2017, Paul Koning via cctalk wrote:
>> 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.
>
> Floppy? not rigid?
Yes, floppy. No sleeve, just the magnetic disk.
> THANK YOU!!
> I actually do love to be proven wrong!
> (so long as there are details like this!)
>
> Are there any pictures?
I haven't found any yet. Will ask.
paul
