Path: utzoo!utgpu!watmath!watdragon!violet!afscian
From: afscian@violet.waterloo.edu (Anthony Scian)
Newsgroups: comp.sys.ibm.pc
Subject: Re: DEBUG bug
Message-ID: <14109@watdragon.waterloo.edu>
Date: 26 May 89 15:00:56 GMT
References: <514@philmtl.philips.ca> <2611@solo3.cs.vu.nl>
Sender: daemon@watdragon.waterloo.edu
Reply-To: afscian@violet.waterloo.edu (Anthony Scian)
Organization: U. of Waterloo, Ontario
Lines: 19

In article <2611@solo3.cs.vu.nl> msschaa@cs.vu.nl (Schaap MS) writes:
>>Go into DEBUG and enter and *trace* through the following instructions with
>>DEBUG on an 80286 or 80386 based system:
>>
>>           MOV   BX,FFFF
>>           MOV   AL,[BX]
>>
>>In trying to display the data contents DEBUG accesses a *word* and causes a
>>segment overflow trap which hangs the machine!
You can thank Microsoft for this behaviour because they used Intel 
reserved interrupts for their own purposes (MS-DOS). 
Any interrupt under 20h is reserved by Intel for future architectural
enhancement.
I think the interrupt that occurs in this case
is a disk I/O BIOS (I don't have an Intel manual here so I could be wrong).

Anthony
//// Anthony Scian afscian@violet.uwaterloo.ca afscian@violet.waterloo.edu ////
"I can't believe the news today, I can't close my eyes and make it go away" -U2