On Wed, 18 Aug 2004 09:33:27 -0400, "J. Clarke"
wrote:
*snip*

Nope. Doesn't work. I don't recall what was different about the Mac
hardware but there was something--the only way you could write a
Mac-formatted disk on a PC was to use a Central Point Software Deluxe
Option Board which provided the necessary hardware.

What was different about the Apple/Macintosh floppy drives
were that they were variable RPM drives whereas PCs simply spun
the floppy disk at a fixed RPM. This design decision was made, IIRC,
because Jobs wanted to not "waste" floppy disk space and to
simplify the electronics needed to read and write data to the disk.
Without telling you EVERYTHING I know, on a constant
RPM disk, the surface velocity of the media is rather greater
at the outer edge than at the inner edge of the writable area. Now...
this means that the read/write circuitry needs to be more complicated,
so as to be able to do its thing reliably both at the outer and inner
sections of the disk. Jobs went with simpler read/write circuitry,
and instead varied the RPM of the disk, slowing it down as the heads
moved out towards the outer edge. This meant that the surface
velocity of the media stayed "constant" no matter whether the heads
were at the center of the disk or the outer edge. It not only
makes the timing circutry simpler for determining where the bits are
at, but, eliminates some power control circutry that controls how much
electricity gets pumped through the heads.

I predict you'll boot it, realize how brutally slow it is, squint at
the tiny screen, and wonder why you went through the trouble!. Good
luck with the macquarium, it sounds like a cool project!

Some people collect old machines for reasons having nothing to do with
current utility. I suspect that 20 years from now that machine's going to
be worth a lot more working than it will as an aquarium.

Yea...I, for one, would LOVE to have a working IMSAI 8080 for
my (admittedly small) collection. However, every time they appear,
they seem to go for well over $1000...which is too much for me to
spend on a whim.
To continue the drift a bit, one of the things I really liked
about my CP/M system (a z80 based, COmpuPro system named helen), was
that it was really the last computer that I truly felt "in control"
of. I was able to keep a picture of the internal workings of the OS
and BIOS in my head, and, was able to re-program it to work the way
*I* wanted it to work. Although it is a trivial thing these days,
it was an exciting moment for me when I was able to re-write the BIOS
(in assembler, by the by) to change the keyboard input from a polled
system that came "standard" to an interrupt driven system. It worked
like a charm and made my life a LOT happier.
That was a good system and still runs, although it is so
limited that I really don't use it any longer, and, probably could not
program a simple serial IO routine in assembler any longer. Actually,
had some business decisions been made differently, I suspect that CP/M
would not only still be around, but, it would have evolved much as
PC/MS-DOS changed. There were extensions that were exploring the idea
of a hierarchical filesystem when it was drowned by the flood of
machines from IBM.
Regards
Dave Mundt