[sebhc] Heath Hardsector disks

Lee Hart leeahart at earthlink.net
Fri Feb 4 00:18:14 CST 2005


Dave Dunfield wrote:
> 
> >I recall an article (possibly Sextant about 1985) about a hardware mod to
> >the heath drives allowing them to read soft sectored media. I'm kinda rusty
> >on this but it seems the heath disks had 10 holes, 9 equally spaced and one
> >of which was half spaced between. The hardware generated the pseudo holes by
> >some sort of multi-vibrator timed off the single hole. Does that ring a bell
> >with anyone? Roger B.

It was the reverse of this. The published circuit allowed you to use
physically hard-sectored disks (with 11 holes) with the soft-sector
controller (which expected 1-hole disks). The idea was that you had
100's of hard-sector disks when you bought your new soft-sector
controller, and could re-use these disks.

I have this circuit in my H89. It works as described. I can insert a
hard-sector disk, and format it as if it were soft-sectored. OF course,
the drawback is that this disk is a "freak" that can't be read on any
other computer unless it also has this hardware mod.

Physically, the mod is a dual one-shot and a gate. Each pulse from the
index sensor triggers the first one-shot. Its timing is chosen to time
out before the next sector hole. But when the true index hole comes
along (between two sector holes), the one-shot is still on. The
occurrence of a hole when this one-shot is already on triggers the
second one-shot. This one creates the fake "index" pulse for the disk
controller.

I also have the software installed from a second article; that connects
*both* the Heath hard-sector and soft-sector controllers to the same
disk drives. The same physical drives thus have two names; A: B: C: if
you insert a soft-sector disk, and D: E: F: if you insert a hard-sector
disk.
-- 
"Never doubt that the work of a small group of thoughtful, committed
citizens can change the world. Indeed, it's the only thing that ever
has!" -- Margaret Mead
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Lee A. Hart  814 8th Ave N  Sartell MN 56377  leeahart_at_earthlink.net

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