ISA MFM disk controllers (From 19Jun09)

Fred Cisin cisin at
Sun Jun 21 18:30:18 CDT 2009

On Sun, 21 Jun 2009, Robert wrote:
> IIRC, the debug commands worked with XT controllers. It seems that the
> debug commands will not work with the newer AT controllers that have
> their own BIOS.

The DEBUG commands were never completely standardized.  Although there
were a lot of controllers that used same or similar commands, there were
always exceptions, such as the original IBM Xebec

> Also, aren't you talking about 5 1/2" drives? I thought that the smaller
> 3 1/2 drives were IDE drives, not MFM.

Not all.  There were still a lot of MFM 3.5" drives.
I even have one machine here with a ~100M ESDI 3.5  If I remember
correctly, the controller on that machine is a WD ?????07
Since ESDI, MFM, and RLL had virtually identical cabling and connectors,
it's a good idea to look up any drive before connecting.

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