Re: Disk transfers help please

[pausch@saaf.se (Paul Schlyter)]

In article <%AkM0C17OH@khar-pern.talamasca.ocis.net>,
Michael Deutschmann  <michael@talamasca.ocis.net> wrote:

> On Sat, 9 Jul 2005, Simon wrote:
>
>> 2/ Most of the B-Sides seem to be unrecognized on the 5.25 PC drive -
>> once I have inserted the disk, the drive never stops, and the transfer
>> tells me all the sectors are bad. Am I doing something wrong ?
> 
> This probably has nothing to do with the fact that you are dealing with
> Apple disks -- rather it's that PC hardware doesn't like flipped disks
> period.
> 
> Years ago, when my family was transitioning to PC from Apple, I was
> frustrated that I could not do a single-side PC format of the unused back
> side of a disk (the front side being in use by the Apple).  I strain to
> recall, but I think the symptoms were similar to yours -- a long spin, and
> eventual errors.
> 
> I think the problem has to do with the index hole -- the little hole in
> the envelope which is next to the large round hole where the motor grips
> the media inside.  This hole is aligned with a second hole in the media
> itself -- the two holes match up once per revolution, and some hardware
> can detect this.  Some computer systems used the index hole to find
> sectors based on the specific position on the disk surface.
> 
> The index hole is through both sides of the disk envelope (so it can be
> read by a light beam), but it is asymmetrically positioned, and most
> floppies only included a single hole.  So if you insert the disk upside
> down, the index hole will be on the left side instead of the right, and
> the drive will be unable to see it.
> 
> The Disk ][ doesn't use this feature, so Apples work fine with flipped
> disks (assuming the media itself is OK on the flipside).  PC's apparently
> freak out, because the drive mechanism doesn't see any pulses from the
> index sensor when the drive spins.  It looks to the hardware as if the
> motor is broken.
> 
> ---- Michael Deutschmann <michael@talamasca.ocis.net>

The Apple II floppy disks were quite unique in not using this index hole
at all.

Back in the days of the Apple II, floppy disks came in two flavors:

"Soft sectored" - one index hole in the disk

"Hard sectored" - 16 index holes in the disk, one per sector

For any other type of computer, it was important that you got soft
sectored floppies if your system required that, and hard sectored
floppies if your system required that.  Hard sectored floppies
were in the monitory though, and a few years later they vanished
completely.

But since the Apple II didn't use the index holes at all, it didn't
matter whether you got "soft sectored" or "hard sectored" floppies
for your Apple II - they both worked fine.

I had a few hard sectored floppies for my Apple II - perhaps one
or two - which I used.  They wored fine.

But the Apple II was unique in the respect.  For any other
computer system you had to get the right kind of floppy,
with one or 16 index holes in the disk itself, or else the floppy
wouldn't work.

-- 
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