What is the Difference Between a BIOS Chip and a CMOS Chip?

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In summary, the BIOS chip stores the BIOS (a program that contains instructions for checking hardware and starting an operating system) and the CMOS chip stores the CMOS settings (things like boot order, and user and supervisor BIOS passwords). If the BIOS is not saved to the CMOS chip, the computer will not boot. The BIOS chip and the CMOS chip are not the same thing.
  • #1
Math Is Hard
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I have some trouble understanding the CMOS chip and the BIOS chip. Some of the terminology throws me, for instance when "go into CMOS" and "go into the BIOS" are used interchangeably.

Here's how I think it works:

The BIOS chip:
A "system rom" chip, non-volatile memory
Contains firmware that can be updated by "flashing the BIOS", but is done rarely
Contains the BIOS (instructions for checking hardware and starting an operating system)
Contains a "CMOS set up utility" for changing BIOS settings

The CMOS chip:
Volatile memory, persists as long as it has battery power
Contains the BIOS settings (things like boot order, and user and supervisor BIOS passwords)
Holds date and time information

Am I on the right track?

I got further confused last week when a friend was telling me that the BIOS chip and the CMOS chip are the same thing.

Thanks.
 
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  • #2
The terminology is mostly wrong - it comes from people building cheap clones copying each others documentation and stuff that is just out of date.

The bios (a program) used to be stored on an eprom with the settings stored in a low power memory (CMOS) which was kept alive by a little watch battery on the motherboard - which also powered the clock when the computer was turned off.

Now the whole thing, the bios program and the settings are stored in flash memory (the same stuff as your usb key or memory card) this makes it much easier to update the bios program to a newer version. You generally don't bother unless there is a specific fault that the new version fixes or some useful feature - if it ain't broke ...

Similalrly there are a 100 and 1 tuning parameters on a modern PC - especially a high performance one which allow you to tweak it's performance. Unless you have no life and enjoy spending the weekend adjusting them so that your machine is 1% faster than some other loser's on the internet - you just select 'default' in the setup screen.However none of that matters.
You go into the setup screening by hitting whatever magic key combination at startup.
If you have screwed up the machine that it won't boot there will be a jumper somewhere on the motherboard that says "bios reset" or "cmos reset".

Pulling the battery out doesn't necessarily clear the settings anymore
 
  • #3
Thanks, NS.

So, what is the battery powering if the BIOS plus the settings are all stored in flash memory?
 
  • #4
Math Is Hard said:
Thanks, NS.

So, what is the battery powering if the BIOS plus the settings are all stored in flash memory?
The clock
 
  • #5
NobodySpecial said:
The clock

AHhhh, OK, thanks! :smile:

*hits self over the head*
 

1. What is the difference between a BIOS chip and a CMOS chip?

The BIOS (Basic Input/Output System) chip is responsible for storing and executing the initial boot-up instructions for a computer. It is a non-volatile memory chip that contains the firmware for the computer's motherboard. On the other hand, the CMOS (Complementary Metal-Oxide-Semiconductor) chip is a type of memory chip that stores the computer's basic hardware configuration, including date, time, and system settings. It is powered by a small battery on the motherboard, allowing it to retain its information even when the computer is turned off.

2. Can the BIOS chip and CMOS chip be replaced or upgraded?

Yes, both the BIOS chip and CMOS chip can be replaced or upgraded. However, it is a delicate process and should only be done by a professional. Replacing the BIOS chip requires specialized equipment and knowledge, and a mistake could render the computer unusable. Upgrading the CMOS chip can be done by replacing the battery or using software to update the settings.

3. What happens if the CMOS chip battery dies?

If the CMOS battery dies, the computer will lose its hardware configuration and system settings, such as the date and time. This can cause the computer to display errors or prevent it from booting up properly. To fix this issue, the battery needs to be replaced.

4. Can the BIOS chip and CMOS chip be reset?

Yes, both the BIOS chip and CMOS chip can be reset. To reset the BIOS chip, you can remove the battery from the motherboard or use a jumper on the motherboard. To reset the CMOS chip, you can remove the battery or use software to reset the settings. However, resetting either of these chips should only be done if necessary, as it can potentially cause problems with the computer's functionality.

5. Are there any security risks associated with the BIOS chip and CMOS chip?

Yes, there are potential security risks associated with the BIOS chip and CMOS chip. Since these chips store important system and hardware information, they can be targeted by hackers to gain access to a computer or steal sensitive data. It is important to keep these chips secure and regularly update their firmware and settings to prevent any potential security breaches.

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