Interaction between bios and CMOS

[bwanaaa]

Yes I have read the wiki and searched the net, but I am missing something. As I understand it, The CMOS retains specific values that the bios reads to boot the machine. The bios is a programmable rom that really cannot be changed from within the 'bios setup'. When we pres the del key and enter the 'bios setup' we are really entering the cmos setup. This is where we set our clocks, our voltages, which hardware is enabled and other properties of the hardware. I am not speaking of UEFI and for now let's pretend it does not exist for clarity.

When a mother board executes the bios instructions, it retrieves values from the CMOS. The CMOS is a RAM chip that is powered at all times- usu by a watch battery when the pc is off. I assume that that specific data is stored at specific offsets in the cmos. Programs like CPU-Z, AIDA, etc can also access these memory locations to tell us about our hardware parameters.

However, for the computer to run the bios instructions, it has to be powered up. Is the voltage, clock speed, and other operating parameters of the bios chip affected by the CMOS settings?

In other words, when I overclock my PC, does the bios execute faster?
Also, If a bios is modified and the computer is booted without 'clearing the CMOS', can the previous values in the CMOS caused the new bios to crash?

 

[Kougar]

Code in it may execute faster due to the higher processor speed, but that's about it... the CMOS just stores settings, as you say. Take the CMOS battery out of the computer and the computer will still turn on just fine but without any default settings. There are still settings hardwired into the BIOS or UEFI, it just takes longer for the BIOS to initialize itself and the system, and of course any optimizations & settings are both lost.

And yes, it's possible previous values can affect a modified BIOS. This is particularly true of BIOS updates and is why any manual recommends users load BIOS defaults after flashing the BIOS. It happens with firmware updates in other devices as well, such as routers.

 

[bwanaaa]

tnx, i thought as much but wasnt sure.

 

[john3850]

Old site with good bios info.
http://www.bioscentral.com/