How to Clear CMOS to Reset BIOS Settings

Documentation

Troubleshooting

000025368

11/14/2018

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What is CMOS?

Complementary metal-oxide-semiconductor (CMOS) is a small amount of memory on a computer motherboard that stores the Basic Input/Output System (BIOS) settings. The BIOS is the software stored on the memory chip on the motherboard. It instructs the computer on how to perform a number of basic functions such as booting and keyboard control. The BIOS is also used to identify and configure hardware in the computer.

For no boot or no display issues, clearing CMOS may help recover the boards because that restores the BIOS default settings.

How do I clear CMOS?

Two ways to clear CMOS:

  1. Using a CMOS jumper or a dedicated jumper on the motherboard, generally near the battery. The jumper position, time to wait, and location of the jumper are completely dependent on the motherboard.
  2. Removing the battery.

See steps for the two methods listed below.

Steps to clear CMOS using the jumper method
  1. Power off the system.
  2. Open up the system so you can see the motherboard.
  3. Locate the CMOS jumper by referring to the motherboard manual and how to clear the CMOS. In general, the CMOS jumper is three pins located near the battery.
  4. In general, CMOS jumper has positions 1–2 and 2–3. Move the jumper from the default position 1–2 to position 2–3 to clear CMOS. Wait 1–5 minutes then move it back to the default position.
  5. Power on the system. In some systems, you might need to enter BIOS to reset to the factory defaults.
Steps to clear CMOS using the battery method
  1. Turn off all peripheral devices connected to the computer.
  2. Disconnect the power cord from the AC power source.
  3. Remove the computer cover.
  4. Find the battery on the board. The battery may be in a horizontal or vertical battery holder, or connected to an onboard header with a wire.
  5. Remove the battery:
    1. If the battery is in a holder, note the orientation of the + and on the battery. Gently pry the battery free from its connector.
    2. If the battery is connected to an onboard header with a wire, disconnect the wire from the onboard header.
  6. Wait 1–5 minutes, then reconnect the battery.
  7. Put the computer cover back on.
  8. Plug the computer and all devices back in.

Example of battery onboard:

Battery onboard
 


Example of battery connected to an onboard header with a wire:

battery with wire

Related topic
Troubleshooting No Display and No Boot Issues on Intel® Desktop Processors