15 Sep
2015
15 Sep
'15
9:17 a.m.
The PLATO IV terminals (the hardwired Magnavox ones,
not the later microprocessor based
ones) had an optional "Audio player". That used a floppy disk of about that
size, storing
analog audio snippets (in analog form, not digitized -- remember, this was around 1972).
Seek was done by a pneumatic D/A converter, essentially. There were 128 tracks, each
with 32 sectors.
Those disks had no sleeve -- you'd just slide the bare magnetic disk into the player
mechanism.
I have an office dictating machine here, I think it is badged 'Olympia' which used
magnetic disks. It
appears that the disk had a spiral groove cut in it, like a gramophone record, the
magnetic head ran
along this [1] and could be lifted and repositioned (like the tone arm of a gramophone) to
skip long
distances forwards or backwards.
[1] I have heard of a similar machine with a sprial 'cam' as part of the machine
to guide the head, this
does not have that or any evidence of it. The magnetic head does the guiding.
I do not have any disks for it, but from the user guide (which I do not know what happeend
to) the normal
disk was 'rigid' (I assume hard plastic), there was also a flexible version for
sending by mail. From the size
of the slot and turntable, I think the disk is about 7" diameter,
I think with this machine you just inserted the 'naked floppy'. No sleeve.
I don't know the exact date, but from the technology used (a pair of B9A based valves
and
contact-cooled metel rectifiers) I would guess early-mid 1960s.
-tony