ISA ( PC ) 8" floppy disk CONTROLLER ???

tony duell ard at
Wed Feb 4 14:52:50 CST 2015

> One effort to help a little is "write precompensation".  On inner
> tracks, if adjacent flux transitions that would end up real close
> together are written slightly out of position, slightly further
> apart, it can help reduce the problem of flux transitions being
> too close together.  As part of doing that, there is a signal
> available called "TG43" ("track number greater than 43") to help
> decide when to enable precomp.

In every 'normal' floppy disk system (read : ones using shugart SA400 or
SA800 type interfaces), write precompensation is done by the controller 
electronics, not the drive. So while an LSI controller chip may well have an
output to enable the precompensation electronics on the controller board
that would not be a reason to pass it to the drive.

On standard 8" drives, the TG43 signal on the interface connector does,
as Chuck said, reduce the write head current.


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