[Coladam] reading ADAM disks in PC drives

Rich Drushel drushel at apk.net
Tue Jan 26 18:57:45 CET 2010

On Mon, January 25, 2010 2:36 pm, Joe Blenkle wrote:

> Not possible...but this is a limitation of ADAMem...not Virtual ADAM...if
> Steve gets around to completing a standalone emulator, it may be possible to
> read ADAM disks in your PC drive. I remember him saying something about it,
> but I don't remember if it was because it COULD be done or it COULDN'T be
> done...

    It *CAN* be done, assuming that the PC OS gives you direct access
to the floppy drive hardware (see ADAMserve source).  Piece of cake
under MS-DOS, or the DOS box under OS/2 (I debugged ADAMserve from OS/2),
but Windows 9x and up did not correctly virtualize the hardware so you
were stuck.

    I *BELIEVE* (failing memory, no time to consult docs) that 1.44 MB
ADAM disks are fully accessible with ordinary DOS function calls (INT 21H
style).  Any of the ADAM double-sided 5.25" formats, however, can only be
read on one side, due to an unfortunate bug in the formatting firmware for
the original Orphanware 320K disk drive, and stolen/propagated for all
competitors.  The 2nd side is formatted with an erroneous value in the
"head" field for all sectors on the 2nd side.  ADAM firmware ignores the
value, but DOS firmware does not and returns an error.  The ADAMserve floppy
disk I/O code bypasses DOS I/O and talks directly to the floppy controller,
so it can correctly ignore the erroneous value.  You can use DOS FORMAT.COM
to make a 320K 5.25 disk which does not have the "head" field mismatch and
ADAM drives will happily use it.  Unfortunately, there are too many original
ADAM disks in the field, so a practical PC floppy reader has to be able to
deal with the format error.

    I know nothing about hardware programming in modern verisons of
Windows, so I have no idea how you would write a device driver for a
traditional floppy disk.  Dale Wick is far more current hardware-wise
than me.


Richard F. Drushel, Ph.D.            | "They fell:  for Heaven to them no hope
Instructor and Executive Officer     |  imparts / Who hear not for the beating
Department of Biology, CWRU          |  of their hearts."
Cleveland, Ohio  44106-7080  U.S.A.  |         -- Edgar Allan Poe, "Al-Aaraaf"

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