In message , Paul
writes:
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If you read the Wikipedia article on floppy, you'll
find there are plenty of variants. Interworking is
not a property of them.

In some cases, it's actually media differences. The magnetic properties

I remember even seeing a hard-sectored 5.25" floppy. (Most such had one
hole in the index track: it synched an oscillator when it passed the
sensor in the index hole, and other sectors were when a certain time had
passed. This one had multiple holes.
aren't the same (from the various eras). The same thing happened

I don't remember that, other than the difference between low-density
(360K for 5.25", 720 for 3.5", for IBM PC use) and high (1.2M and 1.44M
on IBM PCs). [The 3.5" floppies had an extra hole in the case, for the
higher density IIRR; the 5.25" ones didn't.] For machines other than PCs
(Amstrad, BBC, Commodore, ...), I think it was mostly a
layout-of-sectors (and index [directory] structures) rather than actual
magnetic variation, though I guess there might have been some such.

with optical drives and media. Original CD drives could not read CD-RW
media, because nobody imagined the existence of such at the time. A
different laser power was required. Laser diodes now, have a power

I don't think it was so much the _power_, as the _colour_; CD-Rs (and
RWs) have a decided colour cast, whereas stamped CDs (mostly!) don't.
(The writable ones probably _do_ need a bit more power to read them too
- certainly if the laser colour isn't optimised for them.)

There's also the format: you can write CD-RWs and CD-Rs in different
formats from CDs. (Even if you used the right format, unless you wrote
it all at once, the reading drive had to have "multisession" firmware,
otherwise it would either only read the files written in the first
session, or none at all.)
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With floppies, there were 360K, 720K, 1440K, and some Japanese
standard which might have been a higher value (and perhaps a different
drive). I have some motherboards, that they came out of the box,
set for the Japanese standard, and needed to be set to something

And Microsoft's own one that got _slightly_ more than 1.44 on a floppy
(I don't _think_ it was "the Japanese one" [was that 2.88?]; it was only
about 10% more, IIRR). I _think_ they used it just so that the number of
floppies needed to hold Windows 95 - which could be bought on floppies -
was reduced slightly. (The first at least floppy in the set was at
standard 1.44, and included software to control the drive to get the bit
more.) (Oh, it probably made copying more difficult, too, which they'd
want.)
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some of those other platforms I'd never owned, which happened to
use a different drive.

My Oric Atmos - and one of the early Amstrad word-processors (a complete
machine, not a piece of software) - used 3" drives, not 3.5". (A more
solid structure, IMO - didn't catch on though.)

Paul
John
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

"If just one child is saved, then we'll have created a police state for the
benefit of just one child."