Re: Pet 8088 coprocessor board for sale on Ebay

From: Michał Pleban <>
Date: Mon, 17 Jan 2011 18:42:43 +0100
Message-ID: <>

W dniu 2011-01-17 18:03, Bill Degnan pisze:

> Yes, there's something happening strange with that disk.  When you are in 
> native CBM-II mode all you see are the two PRG files, BOOTMS.PRG and 
> MSDOS.PRG.    Is the entire MS DOS in MSDOS.PRG?  BOOTMS.PRG I suppose sets 
> up the environment.  Does what I am asking make sense?Has anyone here taken 
> the D80 file and made a bootable disk?  Yes (I have the system packed away 
> at the moment, but I am getting itchy to test it out given the 
> on-topic-edness.

No, MS-DOS is not in MSDOS.PRG. MSDOS.PRG is only the 6509 loader. I
tried to disassemble it, only got into first few bytes so far. I see
that it loads the 8088 code directly from disk sectors and puts into
RAM, then launches the 8088. Then it contains lots of other stuff I had
no time to disassemble, probably all the IPC interface on the 6509 side.
MSDOS.PRG is a binary file, which is loaded by BOOTMS.PRG, a BASIC program.

The disk is "strange" because it's dual CBM DOS and Microsoft FAT. The
actual MS-DOS files are in the FAT filesystem, which (as all FAT disks)
starts at the first track. It can coexist with CBM DOS, because CBM BAM
and directory are in the middle of the disk, so they don't collide.

If you look at the D80 file with a hex editor, you will see the FAT
table starting at $0100, then FAT copy starting at $0300, then MS-DOS
directory starting at $0500. Looking at the FAT contents and file sizes,
I conclude that FAT clusters are of 2 kB size. But I can't quite figure
out which physical sectors correspond to FAT clusters. There are some
strange one, two or three-sector gaps filled with 00, and I can't
comprehend that. You can see that at $50F5 is the message "INIT TABLE
BAD" that we are looking for, and from FAT allocation data it appears to
me that this belongs to MSDOS.SYS file. But I cannot really see which
exact sectors comprise this file.

Perhaps there could be a way to dump a file from MS-DOS to the AUX
device, which should correspond to the RS-232 port, but I don't know
whether Commodore really made this device assignment, and if so, what
are the baudrate and other parameters.

I tried to debug the RECV.EXE program and indeed it tries to read
something from the AUX device, so I hope that indeed it is the RS-232
port. Still no idea about baudrate etc.

BTW, yes, I took the D80 file I got from Ed Shockley, and I put in onto
a diskette to make a bootable disk. I did it with cbmlink, there were no
problems with that.


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Received on 2011-01-17 18:00:22

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