Looking for a ST419

Tony Duell ard at p850ug1.demon.co.uk
Thu Oct 30 14:16:00 CDT 2008

> 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.


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