15 Nov
2007
15 Nov
'07
7:49 a.m.
On 14 Nov 2007 at 12:18, Lee Inness-Brown wrote:
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.
Let's see--33,000 RPM is 550 rev/second or about one rev every 1.8
milliseconds. To get that down to 60 microseconds max (2*30) you'd
have to pack 36 heads per track. That's a lot of heads on a 12"
disk!
Cheers,
Chuck