21 Jan
1999
21 Jan
'99
4:29 p.m.
On Fri, 22 Jan 1999, Tony Duell wrote:
[80 track 5.25" disks]
> And they're pretty common on non-MSDOS systems. I far more 80-track DS
> drives than 40-track of any flavour.
What the CP/Mers used to refer to as Quad Density.
I've got a number of old IBM PCs and XTs so there
are some 40 track
drives around here, but also looking about I see a lot of 80 track drives
- TRS-80 model 4, Sirius, Gemini, BBC micros, Torch XXX, etc, etc. The
Whitechapel MG1 currently has a 3.5" drive in it, but I have the original
5.25" 80 track drive as well.
Ouch!. I need to find a source of these disks...
So what an I doing wrong?
Don't know, Tony. All I can suggest is to degauss them first, but you
probably do that anyway.
- don
Interesting! I have never had a problem using even generic 48tpi disks
at 96tpi.
- don
Nor have I, usually. I tend to treat all double-density 5.25" disks the same. Some of
the old ones I have were converted to be "flippy" 40-track,
and some time ago I found one such without a label. Not knowing whether it
really had been formatted flipped, I tried it out, using the
by-now-standard 80-track DS drive and a two-step circuit, and found it had.
"OK, so that's a flippy", I said to myself. A little later, I re-read
the
catalogue -- and got a different listing! I had inadvertantly catalogued
side two, with the disk right-side-up -- and realised that the tracks must
not line up, so side two had two sets of data, going in opposite rotations,
with the tracks interleaved!
So I have a three-sided 40 track disk :-)
Kersqueeble (or something).
I seem to remember that the track 0 (say) on the 2 sides of the disk
doesn't line up on a true double sided disk. I also seem to recall that
it's not offset by a whole number of tracks. I wonder if that's what
happened to you - you interleaved the tracks written by the 2 heads on
the 2 sides of the disk.
No I am not going to try it.
Talking of flippies, the 3" drives were stupid. All disks were double
sided. Single head disks used them as flippies - some drives even detected
the position of a notch in the disk and changed the colour of the drive
active LED so you could tell which way up the disk was . Double-head
drives had a little bracket that fitted into that notch and prevented you
putting the disk in upside-down.
So if you had flippy you could read side A in a double-head drive. But
you couldn't read side B - it was spinning the wrong way to read it with
the disk the normal way up and you couldn't turn it over to read it as a
flippy. Well, you couldn't until you dismantled the drive and applied
pliers and cutters to the bracket :-)
-tony