ST-506 hard drive emulation

[Jules Richardson]

On Tue, 2005-07-26 at 19:15 +0100, Pete Turnbull wrote:
> On Jul 26 2005, 14:42, Jules Richardson wrote:
> 
> > I'm not sure how complex such a box would be. I *think* an ST506-
> > interface drive looks pretty much like a big floppy, just with more
> > heads. Far as I know, it doesn't do anything intelligent on the drive
> > itself, just responds to head select / step commands from the
> controller
> > and reads or writes data.
> 
> Yes, except normally the step pulses are buffered, so you can send them
> fast and the drive will handle them at the correct rate.  At least, all
> but the oldest drives do that.  That's the main difference between
> ST506 (not buffered) and ST412 interfaces.

I suppose that's possibly not relevant for a solid-state replacement
though, as the device's ability to virtually step tracks will be far
faster than any controller of the period would produce?

> > The bit I don't know is the nature of the data signal at the interface -
> > it uses +/- signal lines for both read and write data. I'm not sure if
> > that's an analogue signal or a digital one.
> 
> Digital.

Well that bit's easy then :)

> > I don't think there's a need to handle anything complex in the virtual
> > drive. I believe an ST506 drive's purely a data store/replay device and
> > it knows nothing of the actual data stored on it - most of the circuirty
> > on board is presumably just motor control and head amplifiers / filters.
> 
> Correct.

I did just get to puzzling about what sort of sampling rate would be
needed to properly record data from the controller. I suppose the device
just needs enough memory per "track" to match the bit density * platter
circumference of whatever drive's being simulated.

cheers

Jules