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From: perry@omepd.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Code to perform warm reboot.
Message-ID: <424@omepd>
Date: Thu, 19-Feb-87 02:35:54 EST
Article-I.D.: omepd.424
Posted: Thu Feb 19 02:35:54 1987
Date-Received: Fri, 20-Feb-87 07:18:51 EST
References: <3258@j.cc.purdue.edu>
Sender: news@omepd
Reply-To: perry@inteloa.intel.com (Perry The Cynic)
Distribution: world
Organization: Intel Corp., Hillsboro
Lines: 40
Keywords: cold boot, warm boot, IBM PC
Summary: Considering the temperature of a bootstrap

In article <3258@j.cc.purdue.edu> tim@j.cc.purdue.edu (Timothy Lange) 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...]

Let us talk about `Cold' and `Warm' boots. In my book, a `cold' boot is one
that starts from scratch, ignoring any previous state. That's what happens
if you turn on your PC. Part of a Cold Boot is a more or less thorough check
of the hardware. The PC BIOS doesn't do exceedingly much, but it puts the
processor through some simple checking paces, does a memory check and collects
information about peripherals (depending on what type of PC you have).

A `warm' boot, on the other hand, is performed on a running machine. Its
purpose is to restart the system, reloading the operating system. As we
do this from a running machine, there is no need to examine the hardware -
people are unlikely to rip out memory chips or extension boards from a
running PC.

If you think that the difference is insignificant, try a PC where the
memory test takes two minutes. This will change your perspective.

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. Please
wait...

There is a simple way to perform a real `warm' boot on an IBM PC. Just do
an `INT 19H' instruction. This will reload MSDOS and restart the configuration
process (reading CONFIG.SYS, executing AUTOEXEC.BAT etc.) without first doing
the hardware checks. Believe me, it's faster.

The only advantage of a Cold Boot is that you're jumping into ROM, so no-one
can intercept you. Programs can intercept interrupt 19H and delay or prevent
the boot (which may be a good thing for sensitive programs that have to do
cleanup operations). A `JMP F000:FFF0' kills the machine immediately.
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