5 Mar
2002
5 Mar
'02
8:16 a.m.
--- Carl Lowenstein <cdl(a)proxima.ucsd.edu> wrote:
They look like DEC RK03's to me. Predecessor to
the RK05, and actually
re-badged drives from some other manufacturer, the name of which escapes
me at the moment.
Diablo.
RK05's used a glass reticule for positioning.
For the positioner-feedback mechanism, yes. It was a voice-coil
positioner with a detector circuit that would ramp up the coil
so that on a long enough seek, the drive could bring the heads
from zero to max speed, cruise the proper amount, then
slow down
the heads to prevent, among other problems, whiplash, overshoot
and excessive current in the coil windings.
On more than one occasion, I have repaired an RK05 drive by merely
replacing the light bulb behind the reticle.
I think that on-disk format tracks came with the first
"Winchester"
sealed drives.
Perhaps Winchesters were first (I forget what year they were invented),
but the RL01/RL02 drives had embedded servo tracks. Prior to that, drives
like the RM02/RM03 (CDC 9762?) had a servo surface (with an attendant
servo head that could frequently be visually distinguished). The problem
is that for the RK03/RK05, you didn't want to give up 50% of your data
area for servo information, so the packs are hard-sectored (12 sectors
per track of 16-bit words or 16 sectors of 12-bit words) and the
track-to-track positioning was accomplished entirely externally. Makes
it possible to format a blank or disassembled-and-reassembled-with-no-
regard-to-hard-sectoring pack. RL01/RL02 packs are *not* low-level
formattable by the user. When the Air Force would bulk erase them to
protect secure data, those packs were rendered inoperative.
-ethan
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