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From: ast@botter.UUCP
Newsgroups: comp.os.minix
Subject: More on polled keyboards
Message-ID: <1070@botter.cs.vu.nl>
Date: Fri, 13-Feb-87 15:43:43 EST
Article-I.D.: botter.1070
Posted: Fri Feb 13 15:43:43 1987
Date-Received: Sun, 15-Feb-87 00:59:35 EST
Reply-To: ast@cs.vu.nl (Andy Tanenbaum)
Distribution: world
Organization: VU Informatica, Amsterdam
Lines: 20

Re the discussion on polled keyboards- I think that using INT 9 like that is
a dreadful kludge, furthermore it doesn't buy you anything.  Those clones
that are incompatible are incompatible not due to their keyboards, but due to
their disks and other devices.  So to use the BIOS in a multiprogramming
system you would have to find some equally awful kludge to get control away
from the BIOS after it started the disk up, and then catch the disk interrupt
yourself and jump back into the middle of the BIOS to get it going again.

Furthermore, you would have to make sure no other processes made BIOS calls
while waiting for the disk I/O to complete (which can take a looong time on
a floppy whose motor is initially off).  I just don't think a set of weird
kludges, one per device type is a nice way to program a multiprogramming 
system.  These things are complicated enough even when programmed in a
straightforward way.

Another facet of the BIOS issue is that the BIOS performance is not always
stellar.  While this was not top priority in MINIX, a lot of commercial
software bypasses the BIOS (especially the screen BIOS) for this reason.

Andy Tanenbaum