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From: risto@tuura.UUCP (Risto Lankinen)
Newsgroups: comp.sys.ibm.pc
Subject: Re: warm/cold reboot on a IBM-PC
Keywords: reboot, IBM-PC
Message-ID: <605@tuura.UUCP>
Date: 22 Jan 90 09:42:35 GMT
References: <203@inesc.UUCP>
Organization: Nokia Data Systems Oy
Lines: 22

Someone (myself being most inexperienced net-user I couldnt check *who*)
wrote that the PC reboot was equally succesful either with JMP FFFF:0 or
F000:FFF0 .  The MS-DOS debugger revealed another JMP FAR in that location,
but for *any* Intel-based computer this does not apply.

I dont have the relevant Intel specs within reach right now, but I believe
I have seen that documented as a difference between different "x":s in
80x86 processor types.  So, any ROM code expecting a particular segment
preloaded in boot-up will fail if executed with direct jump to an incorrect
segment address.
(Although IBM BIOSes are not such...)

BTW, I have also seen a list of uses for other registers in boot-up as
well.  Just after reset, certain register(s) in 80x86 (or at least 386)
conain information such as CPU version number, microcode checksums etc.
I wonder, if any of the processor detection routines around will utilize
this stuff...

Risto Lankinen


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