14 Nov
2007
14 Nov
'07
8:18 p.m.
I was reading your thread about DDC head-per-track drives.
I had a friend around 1980 that had one of these drives which he had
obtained as surplus from the US Air Force.
It used helium atmosphere around the disks to reduce friction. The disk was
12" in diameter and spun at 33,000 RPM (not a typo), and so it would produce
considerable heat from friction if ordinary air were used, at least that's
what I heard at the time. It was intended as a substitute for magnetic core
(RAM) for mainframes. The disk latency was around 30 microseconds. Because
the driving electronics were a lot slower then, the rated random access
speed was (as I recall) 50 microseconds.
Lee