ST506 and/or ST412 hard drives

dwight elvey dkelvey at
Mon Dec 31 11:22:11 CST 2007

> From: pete at
>> 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.

 Yes, that may have been it. If he is using just one drive,
this shouldn't be an issue.

>> 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.

This is important because many drives that had the auto step, were
really slow using the fixed rate step. I had this problem getting
a ST251 to run on my Olivetti M20. The original drive had a fast step
rate of something like 6 ms. The ST251 wouldn't work faster than
10ms as I recall but the auto rate was much faster.

 I think we need to hear from Andrew to see just what it is he
is talking about. From his original post, I still think he has something confused.

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