ST506 and/or ST412 hard drives

Pete Turnbull pete at
Mon Dec 31 10:45:51 CST 2007

On 31/12/2007 16:23, dwight elvey wrote:
>> From: ard at
>> What signal is that? I've looked at the schematics for thsoe (although
>> not recently) and I can't remember any extra signals on the connector.

>  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.

There's a "drive selected" signal, but I think most drives have that. 
It's there because the 34-way control cable is daisy-chained but the 
20-way data cable is radial, one per drive.

>  I'd suspect things like step rate and number of heads would
> be more important to him than anything else.

The other important difference between the ST506 signals and the ST412 
was that the ST506 didn't support buffered seek; the timing of the step 
signals had to be slow enough that the stepper motor could keep up.  The 
ST412 was the first drive that buffered the step signals, so they could 
be sent rapidly, and virtually every hard drive after that did too.

Pete						Peter Turnbull
						Network Manager
						University of York

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