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Path: utzoo!linus!security!genrad!decvax!microsoft!markz
From: markz@microsoft.UUCP (Mark Zbikowski)
Newsgroups: net.micro.pc
Subject: More on interrupt vector usage
Message-ID: <8668@microsoft.UUCP>
Date: Thu, 3-Nov-83 23:54:27 EST
Article-I.D.: microsof.8668
Posted: Thu Nov  3 23:54:27 1983
Date-Received: Sun, 6-Nov-83 21:35:40 EST
Organization: Microsoft Corporation
Lines: 33


A quote from a recent issue of Info-IBMPC

    "...  [Am I missing something?  IBM uses interrupts in
    the range 0-1F and Intel reserves these.  This seems
    like a problem to me.  -Ed.]..."

Yes, something is being missed, but the problem seen is
only a problem for IBM and for the ISV's who happened to
use the direct calls to the IBM ROM BIOS rather than use
the DOS interface.  The much-publicized issue was NOT whether
or not IBM had used the interrupt vectors but rather that
MSDOS/PC-DOS had usurped them.  To quote from the previous
article in Info-IBMPC:

    "...  Page 2-4 of the I'M manual reveals that MS-DOS
    uses 25 of those 27 reserved interrupt vectors.
    Specifically, MS-DOS uses 5 and 8 through 31
    inclusive...."

This is not the case.  The cited documentation says NOTHING
about MSDOS/PC-DOS using these vectors.  Rather, on the
previous two pages, the document describes these interrupts
as the interface to the IBM ROM BIOS.

On page 2-7, under the heading of 'other R/W memory ussage'
are described the ONLY vectors in use by MSDOS/PC-DOS.

FYI: MSDOS/PC-DOS has been running on several 80188's and
80186's for quite some time without modification.  Only the
device drivers were changed.
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