80386 cache and VGA

Bill Mayhew wtm at uhura.neoucom.EDU
Sat Jun 2 12:48:07 AEST 1990

I know from experience that AT&T (about the same as ISC) Unix will
not boot unless you have a 16 bit VGA controller and that
controller is in a 16 bit slot.  It'll boot from an MDA card too,
of course.

Cruiously, AT&T's 6386 hardware service guide shows the VGA card
installed in an 8 bit slot.  One of our staff people received a
6386 that had been configured by AT&T.  Apparently, they must have
followed the service guide.  It would boot DOS, but when he tried
to install the Unix bundle that came with the machine it would gag.
He called, and I switched the card to a 16 bit slot, and all was

I can't really think of any reason why a VGA card would have
problems with a cache system.  I am running AT&T 3.2.1 on a JDR 33
MHz MCT board with a 64K cache and an OEM verison of the Paradise
VGA Plus/16.  No problems.

Unix does not use the DOS BIOS for anything except to read the
first level bootstrap loader from the hard drive.  The reason is
that DOS BIOSES use software interrupts for virtually everything.
INTs aren't available in protected mode, so the results would be a
real mess.  The DOS BIOS also in not at all reentrant, so the
kernel couldn't use the BIOS anyway.

IBM is an exception.  The model 80 (which the only one I have
personal experience with) has a second BIOS, called, 'ABIOS' which
is accessible from protected mode (A for advanced).  The regular
BIOS is called, 'CBIOS' (C for compatibility).  The ABIOS works by
calling the functions via long jumps sort of a-la CP/M, if any of
you old-timers remeber that.  Perhaps Xenix for PS/2s uses the
ABIOS; that wouldn't surprise me too much given my experiences with
SCO :-).

== Bill ==

Bill Mayhew  Northeastern Ohio Universities College of Medicine
Rootstown, OH  44272-9995  USA    216-325-2511
wtm at uhura.neoucom.edu   ....!uunet!aablue!neoucom!wtm

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