30 Oct
2008
30 Oct
'08
12:16 p.m.
RWC was important with the ST-506 standard, but, IIRC,
it fell
away with the ST-412 standard, and the pin that the controller
used to tell the drive to reduce the write current was recycled
as another head-select line, allowing an ST-412-compatible drive
to have 9-16 heads. More modern drives kept track of which track
they were on and handled RWC internally, sometimes based on the
Write Precomp value, I think.
I doubt that. Precompenation is slightly altering the timing of the write
pulses, and there's no easy way for the drive to detect that. More likely
the drive simply knew what cylinder the heads were on (e.g. by keeping a
count of step pulses inside the microcontroller) and simply reduced the
write current on cylinders beyond a certain value.
I think some drives did the precompensation themselves too, thus the
controller didn't have to bother with either the RWC or the Precompensation.
-tony