[sebhc] hard sector substitute

Steve Thatcher melamy at earthlink.net
Tue Jun 29 05:43:14 CDT 2004

a HD drive is able to read DD disks, so there should be a way to reduce the speed to 300rpm (I haven't looked at the HD interface in LONG time...). I don't think rotational stability will be an issue. If that were the case then DD SS disks would be problematic. The same drive does both HS and SS. The only latency issue with regards to hard sector disks would be the computer response time to "seeing" the index hole and when it really starts writing the sector data. That time will vary a little, but is ignored when drives are being read.

I have been thinking about a PIC that would be able to not only supply the missing hard sector pulses, but also be able to remove them from hard sector disks. The PIC would work for both 5 1/4" and 8" drives and be smart enough to adjust itself based on the index hole. A few jumpers on it would set it for how many sector pulses to generate (1, 10, 16)  and what drive size.

Does anyone else have any suggestions or comments?

best regards, Steve Thatcher

-----Original Message-----
From: Peter <peter59 at sbcglobal.net>
Sent: Jun 28, 2004 8:50 PM
To: sebhc at sebhc.org
Subject: RE: [sebhc] hard sector substitute

The standard single or double density drive rotates at a speed of 300rpm.
High density drives are faster at 360rpm. I don't know the relative
stability of the rotational speed, but would suspect that you may have more
trouble with a high density drive than a double density. This view is NOT
supported by any experience or testing - just a guess on my part ;)

peter59 at sbcglobal.net - http://www.geocities.com/anapro.geo/

> -----Original Message-----
>  Steve Thatcher and I talked about this a month ago. It
> seems like it would be a relatively easy project. One
> could do it with one of those PLL chips and a couple 555's
> from an analog side or just use a PIC to create the pulses.
>  It saves having to find hard sectored disks. It does require
> that the drive be in good shape. The rotational speed
> has to be nice and constant. I don't know what the
> tolerance would be but I suspect it is within the
> range that most drives would work fine.
>  As far as drives go, I'd suspect that a H17 would drive
> either a 720K or a 1.44M. Of course, it wouldn't be
> any faster. That would require a faster processor.
> You'd need to deal with any rotational rate change but
> I'm not sure what these are for these drives.
> As it is now, it is just about as fast as it needs to
> be between writing bytes.
>  I should note that my Z80 machine includes the jumper
> modifications to do double sided disk. If anyone wants
> this information, I can make some notes.
> Dwight

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