Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!rutgers!dayton!umn-cs!hyper!jmh
From: jmh@hyper.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Code to perform warm reboot.
Message-ID: <204@hyper.UUCP>
Date: Sun, 22-Feb-87 15:26:01 EST
Article-I.D.: hyper.204
Posted: Sun Feb 22 15:26:01 1987
Date-Received: Mon, 23-Feb-87 05:44:40 EST
References: <3258@j.cc.purdue.edu> <424@omepd> <1441@bnrmtv.UUCP> <1442@bnrmtv.UUCP>
Organization: Network Systems Corp., Mpls. MN
Lines: 16
Summary: Warm Boot and Extended Memory

In article <1442@bnrmtv.UUCP>, zarifes@bnrmtv.UUCP (Kenneth Zarifes) writes:
>  
> I almost forgot,  the best way to do a warm reboot is to move the value 1234H
> into the location 0040:0072 and THEN jump to F000:FFF0
> 
> You'll find that this works on clones, AT's, PC's and about everything else.

I believe that this machenism is used internally in DOS. Specifically,
on the AT, there are DOS routines for manipulating extended memory.  These
routines switch into protected mode to get to the memory they want.  However,
the only way out of protected mode is a hardware reset.  In order to
avoid the memory checks and delays on the reset, the magic number is
stored at 0040:0072 to control the restart process.

Joel M. Halpern -- Network Systems Corporation
ihnp4!umn-cs!hyper!jmh