Help needed identifying old MFM drives from the excavation

Fred Cisin cisin at
Sun Dec 6 20:51:30 CST 2020

On Sun, 6 Dec 2020, Chris Zach via cctalk wrote:
> As the excavation of Bob's junkpile continues I have finally hit the MFM 
> layer. Specifically about 10 5.25 hard disks that look to be old style MFM 
> drives.
> Vertex V150
> Miniscribe 6085
> ST 4038M Seagate Franklin telecom AT-40
> Miniscribe 3650 HH
> Seagate ST4096
> Priam ID45-H
> Rodime RO203E
> RD54
> Real ST506
> Pair of ST412's.

The Seagates were commodity drives, used in almost everything.
Number is approximately the unformatted capacity.
ST506 was 5MB formatted (305 Cyl x 2 heads) ;
ST412 added buffered seek, was 10MB formatted (306 cyl x 4 heads).
ST4096 was 80MB formatted.  (1024 Cyl x 9 heads)  For a long time, it was 
the most common of the largest drives in that form factor.  I found out 
that 135W XT/AT power supplies were not always happy trying to run two of 
those at a time.

XT/AT MFM had 17sectors per track; 512 bytes per sector.

Drives formatted on a machine other than 5160/5170 are likely to be 
unreadable with 5160/5170.
Drives formatted for a given XT controller were often incompatible with 
another XT controller.  (Was some of that due to numbering sectors from 0 
Vs from 1?)
Drives formatted with an AT controller were normally usable on another AT 

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