ST506 and/or ST412 hard disk drives

Tony Duell ard at
Mon Dec 31 17:57:46 CST 2007

>  I have the same question. The ST506 and ST412 were different
> in the WrPrecomp signal being changed to a head select for
> the ST412. I think he is looking at documents that state that he
> needs a ST506/412 interface. This would be compatable with
> just about any MFM drive made after the ST412.
>  There was a signal on some drives that came on the data cable.
> I think it may have been a write protect but I don't recall
> exactly what it was. The ST506 may have used this signal.
> I'm not sure if this is what he is talking about.
Some, if not most, ST506/ST412 interface drives output a signal on the 
data cable when that drive is selected. The idea was you could plug the 
data cables into the controller in any order, and the controller could 
determine which data connector to use, which receivers to enable, etc. 
It's a pity few controllers made use of that!
I'm not aware of any write-protect signal on the data connector of any 
such drive.

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