What Is CMOS Memory?

What Is CMOS Memory?CMOS is simply an acronym for complementary metal oxide semiconductor. CMOS simply describes the type of material from which this special memory is made. To start successfully, your PC must know specifics about its disk types, available memory, video type, and so on.

When you power off your PC, the information in your PC’s random-access memory is lost. For the PC to remember its key hardware settings, the PC uses a small battery-powered CMOS memory. Because the CMOS memory is batter powered, the memory maintains its contents, even when the PC is unplugged.

How Your PC Remembers Key System Settings

PCs differ by the number and type of disk they contain, the amount of available memory, video type and more. When your PC starts, it must know these key settings. To remember its settings, the PC uses a small battery powered memory called the CMOS. As you perform different hardware upgrades, you might have to update your systems’ CMOS settings. In addition to storing your PC’s hardware settings, the CMOS memory keeps track of your system’s date and time.


Your PC normally uses its CMOS memory settings only when it starts. Depending on your PC type, the way you access the CMOS settings will vary. When you first turn on your PC’s power, the PC performs a self-test of its hardware components. During the self-test, the PC displays a count of its working memory.

Normally, you will access your system’s CMOS settings by pressing one of the following keyboard combinations when your system completes its memory count:

  • DEL
  • EXS

When You Must Access CMOS Entries

As long as your PC starts successfully, you can normally ignore the PC’s CMOS settings. However, if you add memory to your system or install a new or different disk drive, you may need to update a CMOS setting.

Password Protecting Your System

Depending on your system type, you may be able to use a CMOS setting to password protect your system. When you assign a password to your system in this way, your system will require you to type in a password each time it starts. If you fail to type in the correct password, the system will not start.

Should you forget your password, or should you need to access a system for which another user has assigned password protection, remove the CMOS battery. The PC, in turn, will forget its current system settings, including the password. You can then install the CMOS battery and restart the system.


  • CMOS is an acronym for complementary metal oxide semiconductor. In short, CMOS defines the type of material from which the chip is made.
  • Your PC uses a special memory called the CMOS memory to store specifics about your system, such as the number and type of disks, the amount of memory, the video type, and the current system date and time. If you change your hardware configuration, you may have to run the CMOS setup program to inform your computer of the changes.
  • To access your PC’s CMOS settings, you normally press a keyboard combination after your computer completes its power-on self-test. The documentation that accompanies your PC wills specify the keyboard combination your must press.
  • When you display your CMOS settings, write down the current vales. Place your notes in a safe place. Should you ever need to restore the settings, you will be glad you took notes.
  • Like all batteries, your CMOS battery will eventually fail. At that time, you will need to replace the battery and then restore the previous settings.


  1. briefed very well

  2. Theophlilus MunyereMay 23, 2013 at 3:45 PM

    thanks guys I've been helped by your contribution