What Is the Primary Function of the BIOS & the CMOS?

Your computer's Basic Input/Output System (BIOS) and the Complementary Metal Oxide Semiconductor (CMOS) chip that serves as the BIOS' memory handle the process of setting your computer up so that it is ready for you to use. Once it's set up, they also help your computer's parts work together. While you can use the BIOS and CMOS to do more, these basic functions are their key purposes in business-oriented, as opposed to enthusiast-oriented, computers.

Your computer's basic settings get made and stored in the BIOS. Many of them are extremely technical – like the clock speed at which the CPU communicates with the computer or the amount of power to send to it. Others are more mundane – like the system clock's time and date settings. Some are set by you as the user while others, like the types of drives attached, can be automatically set by the BIOS as it senses your computer's components.

While your computer needs to be booted into its operating system for you to access your files and your programs, the BIOS takes care of booting the operating system for you. When you turn your computer on, the BIOS tests your computer's components to ensure that they function. If they are all working, it looks to the appropriate drive for instructions on how to start up the operating system and has your computer start the boot process.

Since the BIOS tracks your system's settings, it knows some fundamental basics about your system, like which internal socket your hard drive plugs into. With this knowledge, it serves as a go-between for your operating system. When your OS or one of its programs needs to communicate with one of your computer's hardware components, it sends the command through the BIOS, which handles sending the command to the right place and collecting the response.

For the BIOS to work properly, it needs to keep information about your system handy. It stores your system's information and its settings in a memory chip referred to as a CMOS chip. Some computers use CMOS chips that retain their information after the power gets shut down, while others use traditional RAM chips that lose information when they lose power. Computers with CMOS RAM will also have backup batteries to keep the CMOS settings.