ast@cs.vu.nl (Andy Tanenbaum) (11/19/88)
Several years ago I rewrote UNIX from scratch. This system, called MINIX, runs on the IBM PC, XT, AT, and many 386 machines. It also runs on the PS/2 model 30, but not on the model 50. The purpose of this message is to see if anyone can figure out why not. The thing which puzzles me is that it works fine on the AT, which is an 80286 based machine, just like the model 50. If the CPUs are identical, the problem must lie in the I/O somewhere. I don't have a model 50 anywhere around, nor do I have any documentation, so debugging code for it is somewhat tricky. It would have been nice if IBM made it compatible with the AT, but they seem to have not done so. Except for the hard disk, for which MINIX uses the BIOS call 0x13, it does all its I/O at the chip level. It directly addresses the NEC 765 floppy disk controller, the 6845 video controller, the clock, the interrupt controller, etc. If any of these things are different than the PC, XT, and AT, that would cause problems. Does anybody have any idea of what the problem might be? If you haven't heard about MINIX, I can send you a blurb. It is available from Prentice-Hall for $80, and includes all the source code in C. There is a large newsgroup, comp.os.minix about it. Thanks. Andy Tanenbaum (ast@cs.vu.nl)