Re: Pet 8088 coprocessor board for sale on Ebay

From: Michał Pleban <>
Date: Wed, 19 Jan 2011 11:30:44 +0100
Message-ID: <>

W dniu 2011-01-19 05:18, Hoffmann-Vetter, Martin pisze:

> Yes, it loads 54 sectors starting at Track 1 Sector 21 to memory bank 1 address 0. After reading sector 22 the next sector is sector 0 on the next track. So it loads IO.SYS at 10000 (6509) or 0000:0000 (8088) and MSDOS.SYS at 11800 (6509) or 0180:0000 (8088).

Correct. In fact, the first kilobyte of IO.SYS are interrupt vectors,
where INT 07h points to 0044:0000. This jumps to 0040:0126, which
apparently initializes MSDOS.SYS by calling 0180:0000, and then uses DOS
INT 21h routines to load the COMMAND.COM file. So INT 07h is the warm
start procedure, triggered by circuitry on the board according to Ruud's

So it looks like actual code of IO.SYS is at segment 0040 and MSDOS.SYS
at segment 0180. Now I am looking at this initialization code with IDA
Pro disassembler :-)


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Received on 2011-01-19 11:00:22

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