On Fri, 2 Sep 2022, geneb via cctalk wrote:
All the discussion around 8" disks reminded me
about a question I've not been
able to find an answer to.
I've got a Qumetrak 842 drive that I use for imaging 8" disks with either
ImageDisk or AppleSauce. When I first tried it out with AS, the listed RPM
was > 7K.
well, 720, not 7K
It turns out that the disk I was working with was a
NOS Dysan that
had both the single and double-sided index windows punched in the jacket.
The 842 has both of those index sensors, so both were being triggered one
after the other. The solution was to cover one of the index windows on the
The question I have is how did a contemporary system deal with the
combination of a disk with both index windows and a drive with both index
THAT is why I asked:
> > How do they handle the issue of how the
drive knows whether it is
> > SS, DS, or SS flippy? Or is it assumed that that problem is for the
> > host FDC?
> > (some DS drives had both SS and DS index sensors, so that they could
> > read SS in the DS drive, and such a drive is going to see TWO index
> > pulses with this disk!)
and Chuck replied:
> I think I was using a Qume 842 to read the disk
and it turned out to
> be double-sided, so there was no problem reading it. The disk itself
> probably arrived here 30 years ago, so my memory may be faulty.
> This isn't the first floppy I've seen with both SS and DS holes,
> however. I recall that using a write-enable sticky over the
> appropriate index aperture resolved the problem of side-edness.
Obviously, it can be left to the user to mask off any extraneous index
hole(s). And a more sophisticated engineering solution was not provided.
Junpers to separately disable each index sensor with an open case, or
brought out to accessible switches would be a "RIGHT" way to handle it.
For reading and writing (not formatting) with a WD controller, you might
not even notice a problem.
But, with a 765 type controller, the long "flash blindness" (which will
happen twice per revolution), means some sectors are likely to be
Once you know whether the disk is SS or DS, then you should mask the
If you are FORMATTING, then YOU know whether you are SS or DS, and know
which hole to mask.
I used right protect tabs, but made sure their adhesive was in good shape!
I was also glad that they changed the write protect/enable notch location.
My first used 8" drive came with a handful of write enable tabs in the
back of the drive. Obviously, Bill Gates' "Computer Bowl" team were
people who had had OTHER people open the case and fish out the tabs that
had fallen off, or never had to re-enable write on a disk.
Well, hardly ever. (cf. "H.M.S. Pinafore", Gilbert & Sullivan)
The 5.25" location was more prone to friction knocking them off, but
easier to get to. And, I had a folded business card handy that I could
wrap over the notch and carefully slide in with the diskette for a
temporary protect. (and drive(s) dedicated to disk analysis jumpered to
disable write enable) SA455 had a simple jumper to reverse write
enable/protect sensing (software distribution went out on no-notch 5.25"
Grumpy Ol' Fred cisin(a)xenosoft.com