All about CMOS and BIOS

CMOS is short for Complementary Metal Oxide Semiconductor. CMOS is responsible for storing the date, time, system setup and other small functions. They are used at the start of a boot process in a computer system that is why it requires a small battery on the system board that provides power to the CMOS chip, even while the computer is turned off so it will not loose all data save on it.

The program saved inside the CMOS is called BIOS, short for Basic Input Output System. BIOS is the program capable for storing the date, time, system setup and other small functions. Through the BIOS, user can configure devices at the start of a boot process in a computer system.

The BIOS is useful especially if the user needs to reinstall a new operating system on the computer. User need to access first the BIOS and configure what it is needed to.

BIOS of new motherboard can be access by pressing any of the following keys on your keyboard during the boot up process.
  • F1
  • F2
  • DEL
  • ESC
  • F10
After pressing the correct key, you should be redirected to BIOS settings screen. below are different examples of BIOS settings screen.

In this type of BIOS, the menus are listed. System time and date could be access by selecting the first option and press enter.

After you press enter key, you should be redirected to this screen where you could change the time and date and see system information about your hard disk drive and other devices.

One important option is the boot sequence which could be configure on this screen. change the values by selecting it and pressing enter and use the arrow keys or press + and - sign.

Another type of BIOS is just like this one above. The menus are in tab format and you could select each menu by pressing right and left arrow key.

The boot sequence could be access under BOOT menu. change the values by pressing enter.

Remember: If you are using a bootable disk as your medium, the boot sequence must by like this:

First Boot Device: CD or DVD
Second Boot Device: HDD

And if you are booting on a bootable flash drive, just change the first boot into USB, then after the reinstallation, you should change again the boot order into this sequence:

First Boot Device: HDD
Second Boot Device: CD or DVD


Sometimes BIOS is inaccessible due to due hardware related issues such as electrical problems or due to inadvertence, such as someone set and then forget the password and the only way is to reverse this. This can be time consuming or frustrating depending upon the motherboard manufacturer and model of the motherboard. So here is my guide if ever this would happen to you. follow my procedure on how to reset or disable the BIOS password.

  1. Read about you motherboard manual and Locate, if possible, the instruction booklet for BIOS jumper setting of your motherboard. If you don't have the manual, then use this site - motherboard references
  2. Make sure you shut down your computer and unplug the power cable from the outlet.
  3. Locate where the BIOS jumpers are located.

4. Take note of the present pin location and the location of the jumper on those pins to determine their default location. Write it down so you will not forget!
5. Move the jumpers from the their default location . From pins #1 and #2 , place the jumper across pins #2 and #3.

6. Leave the jumper in place for 20 to 30 seconds and then return it to its default location
7. Plug the power cord back in and restart the computer.
8. During it's startup (boot) process, press the DEL, F10 or F1 key, (depending on your computer) to get into the Bios/CMOS setup. If you don't know how to access the BIOS, follow this link - Bios Basics
9. The Bios password should be gone!

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