Question about CMOS and BIOS

[Systole]

I've always been one to confuse the CMOS and BIOS. From what I've read thus far, the CMOS is a configuration chip that the system "looks" to when it's first booting. In the CMOS setup interface, you can configure the hardware installed on the computer system. I'm wondering if anyone knows more about the CMOS and how it works with the BIOS.

Thanks.. Nigel

 

[Fencer128]

Hi,

The BIOS is a program. Nowadays it's usually stored on a flash EEPROM. The configuration parameters used by the BIOS program are stored in non-volatile memory. This is usually some sort of battery powered NVRAM (referred to commonly as CMOS - though it usually isn't CMOS tech now as far as I understand). If the battery fails - the configuration data is lost. This is not true of the BIOS program stored on the flash eeprom.

For lots of very technical BIOS info check out the forms at wimsbios.

Hope that helps,

Andy

BTW - Welcome to the forum!

 

[Systole]

Thanks for the help Andy,

So the CMOS configuration chip does not copy anything to the BIOS (EEPROM). It just somehow let's the BIOS know what the system configuration is? I'm gussing that volatile memory does not lose it's information once power is lost, but that NVRAM will?

Thanks for the help,

Nigel

 

[Fencer128]

Originally posted by: Systole
Thanks for the help Andy,

So the CMOS configuration chip does not copy anything to the BIOS (EEPROM). It just somehow let's the BIOS know what the system configuration is? I'm gussing that volatile memory does not lose it's information once power is lost, but that NVRAM will?

Thanks for the help,

Nigel

The BIOS program used on your motherbaord is aware of how to access the configuration data it needs. It is determined by the company who wrote the BIOS along with hardware decisions made by the motherboard manufacturer. All IBM PC compatible motherboards are aware of how to address the BIOS program during the POST sequence. In this way everything works together.

Cheers,

Andy

 

[Peter]

The CMOS RAM is just a few bytes of battery-backed storage where the BIOS remembers what its settings are. Settings are lost when the battery gets weak, or if you deliberately remove the battery or use the "CMOS clear" jumper that disconnects it.

BIOS is software, residing in a (flash)ROM, which in turn is mapped to a given point in the computer's memory map - exactly at the spot where the processor begins executing code when it's first powered up. During its execution, BIOS detects stuff (DIMMs, PCI and AGP cards, USB devices etc. etc.) and reads related settings from this CMOS RAM as it goes along.