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From: dmt@mtunb.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Code to perform warm reboot.
Message-ID: <850@mtunb.UUCP>
Date: Tue, 24-Feb-87 08:51:02 EST
Article-I.D.: mtunb.850
Posted: Tue Feb 24 08:51:02 1987
Date-Received: Fri, 27-Feb-87 06:43:39 EST
References: <3258@j.cc.purdue.edu> <415@omepd> <10075@cgl.ucsf.edu.ucsfcgl.UUCP>
Reply-To: dmt@mtunb.UUCP (Dave Tutelman)
Distribution: world
Organization: AT&T Information Systems - Lincroft, NJ
Lines: 29

In article <10075@cgl.ucsf.edu.ucsfcgl.UUCP> kneller@socrates.ucsf.edu.UUCP (PUT YOUR NAME HERE) writes:
>>>The following is Macro code to make an IBM PC and true compatibles
>>>perform a warm reboot.
>>> [...showing a simple assembler program to jump to F000:FFF0...]
>>
>>By this diction, what you propose (a jump to address F000:FFF0) is a
>>COLD BOOT. F000:FFF0 is the place where the processor begins to execute
>>when it is reset (i.e., when the power is turned on). The first thing it
>>does up there is to run test loops and initiate the memory check.
>
>Isn't it true that you can control whether the memory check is done or
>not by placing a particular value in a special memory location?

Byte 40:72 H (in the BIOS data area) is the system reset flag.  (I first
learned of this from Peter Norton's excellent book, "Programmer's Guide
to the IBM PC.")  It is set to 1234H on a warm boot, and could be
anything on a cold boot.  The BIOS startup code looks at this flag,
and skips things (notably the memory test), if the WORD is hex 1234.

I have looked at a few BIOS[es] (what is the plural of BIOS? :-),
and those I have checked all test the reset flag.  (That's not a
guarantee that every clone BIOS will, but it's a pretty strong indicator.)

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