
How did we make the DOS redirector take up only 256 bytes of memory? - tdeck
https://blogs.msdn.microsoft.com/larryosterman/2004/11/08/how-did-we-make-the-dos-redirector-take-up-only-256-bytes-of-memory/
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tdeck
I ran across this when I was reading about the "CALL 5" interface that exists
in DOS. CP/M [1], the early cross-platform microcomputer OS, provided a set of
BIOS routines that you could invoke by setting up a function number and
arguments in the registers, then executing CALL 5. DOS system calls are done
through interrupts, but in order to make it easier to port earlier 8-bit CP/M
programs, you could also use a version of this CALL 5 interface in COM
programs. To this day, COM programs are supported in 32-bit Windows, which in
my mind means theoretically there might be some CP/M program that would run on
Windows as well with a few modifications.

[1]: [https://en.wikipedia.org/wiki/CP/M](https://en.wikipedia.org/wiki/CP/M)
[2]:
[http://stackoverflow.com/questions/16669352/call-5-interface...](http://stackoverflow.com/questions/16669352/call-5-interface-
on-ms-dos)

