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CMOS vs BIOS

These two components of your PC are often getting confused. Hopefully this will help explain the differences.

The BIOS (basic input/output system) is a chip on your system that contains a program that controls the interface between the CPU and the rest of your system. The BIOS is read during the power on (boot) process and sets up the machine to load the Operating System. It is a EPROM (Eraseable Programmable Read Only Memory) chip. This chip cannont be configured by the user. Some BIOS chips can be upgraded by using a technique known as flashing. This is done to allow the BIOS to support newer hardware.

The CMOS (complementary metal-oxide semiconductor) is a low power RAM chip that holds information about your system. Like any RAM chip (and unlike ROM), the chip needs power to retain its information. This power comes from the motherboard battery when the PC is powered off.

The CMOS stores info about the particular hardware in your PC and certain variable settings. This info is read by the BIOS during the boot process. Which is why they are often confused.

The CMOS settings can be accessed during the boot process. How to access them will vary depending on the BIOS in the machine. Generally there will be a message during the boot process to press some key to enter the Setup. The CMOS settings are usually described in your computer or motherboard manual.

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