David Thatcher wrote:
>
> Tim wrote:
> > The CPM API was mainly done through software
> > interupts with register variables setup to do whatever function you wanted.
> > Paterson duplicated the API functions added some of his own and mimicked the
> > described behaviour. He wanted programmers to be able to port their software
> > very easily from CPM.
>
>
> it was duplicated to the level that the first 100 (hex) bytes ( all
> programs under cp/m started execution at 0100H) contained the
> appropriate cp/m BDOS subroutine call at location 0005H in addition
> to the recommended DOS software interrupt, & most of the 'BDOS primate
> functions', (print character, get key input, print string, etc.) carry
> the same 'a' register 'selector' values.
MS-DOS duplicated CP/M-86 far past duplicating the base page layout.
The first 256 bytes HAD to be identical to allow easy porting of existing
software, but Patterson's 8086 OS used identical modules in BDOS which
were NOT needed for compatiblity. The BIOS jump table at the bottom of
the BIOS was also identical, again for software compatiblity. For those
of you that are interested in digging more deeply into history, there
used to be a newsgroup dedicated to CP/M ... don't know if it still
exists.
Regards,
-Nick T.
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|