> 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
