Awd 4.50G : need a free CMOS RAM byte. Is 34h OK?

by **Czerno** » Wed Oct 25, 2006 10:19 am

I have to put back this old 486 based MoBo into service, Award 4.50G BIOS.

Quick version : can I safely use "CMOS" memory byte #34H for my whatever purposes ? (I Need one free byte, if I'm wrong and 34H isn't free, then advise one).

Additionnal : Do you know where I could find complete spec for CMOS RAM use by this BIOS ? More additionnal : this BIOS's full spec. Even more additionnal : idem for other BIOSes.

TIA

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Czerno

by **NickS** » Wed Nov 01, 2006 6:03 pm

"Award 4.50g" is too generic a description.
Check this link for a "typical" CMOS layout.

by **Czerno** » Wed Nov 01, 2006 8:52 pm

NickS, w/ all due respect, your link is more "generic" than my question! I do know what a "typical" CMOS layout is like, thank you anyway.

If Award 4.50G - the infamous 1994 BIOS with the Y2k problem, which reverts to year 1994 at each boot when the century byte is 20 - is too generic, then what more is needed in order to answer my question ? The precise chipset ? I am correcting the Y2k problem by a home made patch to the partition sector of the boot HD, and for this I needed a safe (untouched by BIOS) register in CMOS. After examination, I found the particular register - 34h - appears not in use, but not 100% sure. I assumed there will be people in this forum who had access to OEM docs from Award - or even a disassembly of a generic 486 Award BIOS.

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Czerno (typo edited)

by **NickS** » Thu Nov 02, 2006 12:21 pm

I expect you understand that 4.50g is just the base Award BIOS product, which is then customised to the motherboard manufacturer's requirements with various goodies added, features disabled, etc. Different chipsets and motherboard features might use differing amounts and locations of CMOS ram for storage of parameters e.g. for chipset or onboard peripherals.

In my experience, the usage of BIOS-specific "reserved" data in CMOS can vary even from version to version of the BIOS for a specific motherboard, let alone chipset. A location unused in one BIOS version might be used in the next as they decide to add or enable a feature. When you upgrade, this change of usage of the CMOS data can be enough to prevent the board from booting. That's why we often advise people to use the "Clear CMOS" switch /cc (and, indeed the other "Clear xxx" switches /cd and /cp) when using awdflash with flashable BIOSes

I doubt that anyone can give you a definitive answer about which bytes of CMOS are free in a given version of the BIOS for a given motherboard, unless they have already done it for your motherboard and version of BIOS. They will not know that unless you post the BIOS ID and OEM message, hence "4.50g is too generic".

Best alternatives, IMO, are 1. to experiment ("suck it and see"), or 2. to go through the BIOS with a hex editor or disassembler looking for accesses to particular bytes, which I guess from the above you have already done.

by **Czerno** » Thu Nov 02, 2006 2:01 pm

NickS wrote:
I doubt that anyone can give you a definitive answer about which bytes of CMOS are free in a given version of the BIOS for a given motherboard, unless they have already done it for your motherboard and version of BIOS. They will not know that unless you post the BIOS ID and OEM message, hence "4.50g is too generic".

Best alternatives, IMO, are 1. to experiment ("suck it and see"), or 2. to go through the BIOS with a hex editor or disassembler looking for accesses to particular bytes, which I guess from the above you have already done.

Understood. In fact I already did "1." with no problems (yet). It's a pity there are no published records of custom CMOS and other resource usage though. I grasp it OEMs can, in theory, customise their machines BIOSes but I doubt most do so more than strictly necessary, and then do it other than choosing from a set of prebuilt options by the BIOS creators. Am I wrong here ?

Regards

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Czerno

by **zapbuzz** » Thu Jan 04, 2007 1:58 am

It's a pity there are no published records of custom CMOS and other resource usage though. I grasp it OEMs can, in theory, customise their machines BIOSes but I doubt most do so more than strictly necessary, and then do it other than choosing from a set of prebuilt options by the BIOS creators. Am I wrong here ?

perhaps a thread or forum could serve as a reference of general public interests from user experiences?