18 Jun
1998
18 Jun
'98
7:43 p.m.
I think that there are some exceptions to that Tony.
The following is a
clip from some correspondence with Chuck Guzis at Sydex a while back:
"Another topic that I'd like to see some commentary on is how people
have handled those old diskettes that lack the Index Address Mark
information, such as those used on the Cromemco C10. On a PC
controller, the first sector on a track on such a diskette usually falls
to be seen by the FDC because it falls in the "blind spot" (ostensibly
PLL sync-up time) of the 765-family chip.
Have you tried using a controller that doesn't need the Index Address Mark,
such as a WD1772 or a NatSemi DP8473 ?
"But 3.5" diskette drives are too difficult
to modify. We've had good
read and write results by passing the index signal through a 1-shot
carefully adjusted to trigger slightly ahead of the actual index
position. But this is a very touchy arrangement, though it does work.
But the Index Address Mark isn't part of the spec for 3.5" disks. I know
most PC controllers put it there, but it's not in the Sony spec, and some
controllers (see above) will work fine without it.
I know that I have experienced the problem of the
first paragraph on more
than the C10 disks.
- don
--
Pete Peter Turnbull
Dept. of Computer Science
University of York