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 [2]: http://stackoverflow.com/questions/16669352/call-5-interface...