[sebhc] H89 BOOT

Lee Hart leeahart at earthlink.net
Tue May 15 22:09:27 CDT 2007

Carroll Waddell wrote:
> If a diskette is bootable (BOTH HDOS AND CP/M) on my H8, should it be 
> bootable on an H89?

The stock distributions of Heath's HDOS and CP/M would boot on either an 
H8 or an H89. But, that was because they took pains to make sure they would.

The H8 came with an 8080 CPU; the H89 had a Z80 CPU. These two CPUs run 
at different speeds and have different instruction sets. Heath wrote the 
BIOS so it would boot on either. But there were switches in the code 
that could select between them (i.e. you could build a new BIOS that 
would be specific to the H8 or H89).

There were also differences in the two machine's boot ROMs. Programs 
that used them (like HDOS) could also have problems running on the 
"wrong" machine.

Another common problem was that the boot code could be configured use 
the wrong terminal baud rate, wrong memory size, wrong disk parameters 
(sides, step rates, 40/80 tracks), or wrong disk controller (H17, H37, 

Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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