ballou@brahms (Kenneth R. Ballou) (10/31/86)
In article <277@puff.wisc.edu> plocher@puff.WISC.EDU (John Plocher) writes: >Notes from other messages: >>And, as I type this, my keystrokes are being processed by those very same >>BIOS ROMs, although my machine is running multiuser Xenix, not PC-DOS. > > WRONG! > > If you are using XENIX, your keystrokes are NOT going through > any ROM routines - in fact, the ROMs are ONLY used at boot time > to determine HARD DISK parameters. > > The Xenix device drivers are totally seperate from any of the > ROM BIOS routines! > > (this info relates to MicroSoft/IBM Xenix 2.0 (SVR2ish) only) In fact, there is just no way one could use BIOS in 80286 protected mode. The point is that the contents of segment registers meansquite different things in protected and in real mode. The BIOS assumptions about how it can use segment registers would almost certainly cause protection violations in protected mode. For example, a common technique used to avoid changing the DS and ES registers is to put data in the code segment (obviously, this is not true in ROM, but is used in device drivers, for example) and to use a CS segment override. This will cause an exception in protected mode, since the processor makes a distinction between code segments and data segments. --- Kenneth R. Ballou ...!ucbvax!cartan!brahms!ballou Dept. of Mathematics University of California Berkeley, California 94720