What resetting CMOS does and when you need it

CMOS is a small chip on your motherboard that stores your computer's basic settings — things like the date and time, boot order, and hardware configuration. Resetting CMOS clears those settings back to factory defaults. Your computer will still work after a reset, but it will forget custom configurations you made in the BIOS (the firmware menu where you change those settings).

You might need to reset CMOS if you forgot your BIOS password, if your computer won't start because of a misconfigured setting, or if you're troubleshooting hardware problems. Some people also reset CMOS before selling a used computer to remove their custom settings. It's not something most people do regularly — only when something specific has gone wrong or you're making a deliberate change.

Resetting CMOS does not erase your files, programs, or operating system. It only affects the low-level hardware settings stored on that one chip. Your Windows or Mac installation, your documents, your photos — all of that stays intact.

Key Takeaways

  • CMOS reset clears only your BIOS settings back to factory defaults, not your files or programs.
  • The most common method is removing the CMOS battery from the motherboard for 10 to 30 seconds, then reinserting it.
  • Some newer computers have a CMOS reset button or jumper on the motherboard instead of a removable battery.
  • After a reset, your computer may boot slowly the first time and you will need to reconfigure any custom BIOS settings you had made.

Locating the CMOS battery inside your computer

Before you open your computer, shut it down completely and unplug the power cable. Wait a few seconds. This ensures you won't damage components with static electricity or an accidental short circuit while you're working inside.

Open your computer case. On a desktop, this usually means removing the side panel — typically held by two or three thumbscrews or clips. On a laptop, you may need to remove the entire bottom panel; check your laptop's manual for the exact steps, as they vary widely by model.

Look at the motherboard (the large circuit board inside). The CMOS battery is a small, round, silver coin-shaped battery about the size of a watch battery — usually labeled CR2032 or similar. It's typically mounted flat against the motherboard in a small plastic holder. On most computers, it's somewhere in the middle or lower portion of the board, but the exact location varies by manufacturer.

If you cannot find a removable battery, your computer may have a CMOS reset jumper instead. This looks like a small plastic cap on two or three metal pins. Check your motherboard's manual or look for a label on the board itself that says "CLR_CMOS" or "PSWD" (password reset).

Removing and reinserting the CMOS battery

Gently press down on the small metal clip or lever on one side of the battery holder. The battery will pop out slightly. Remove it by hand and set it aside on a non-static surface — a wooden table is fine, or you can place it on the cardboard box your computer came in.

Wait 10 to 30 seconds. This gives the CMOS chip time to fully discharge and forget its stored settings. Some people wait longer to be safe; there's no harm in waiting a minute or two.

Reinsert the battery into the holder, making sure it sits flat and the metal clip clicks back into place. The positive side (marked with a +) should face up, which is usually the default orientation in the holder.

Close your computer case, plug in the power cable, and turn the computer on. It should start normally. You may see a message during startup saying something like "CMOS battery low" or "CMOS checksum error" — this is normal and expected after a reset. The computer is simply noting that the CMOS settings have been cleared.

Using the CMOS reset jumper (if your computer has one)

If your motherboard has a jumper instead of a removable battery, shut down and unplug your computer the same way. Open the case and locate the jumper — it will be labeled on the motherboard, often as "CLR_CMOS" or similar.

The jumper is a small plastic cap sitting on two or three metal pins. Using a non-conductive tool (a plastic stick or the handle of a screwdriver), gently remove the cap and move it one pin to the side, so it's covering a different pair of pins. Leave it there for 10 to 15 seconds, then move it back to its original position.

Some motherboards have a three-pin jumper with positions labeled 1-2 and 2-3. Move the cap from pins 1-2 to pins 2-3, wait, then move it back. Check your motherboard's manual if you're unsure which pins to use — using the wrong pins can damage the board.

Close the case, plug in, and power on. The reset is complete.

What happens after you reset CMOS

Your computer will boot into its default BIOS settings. The date and time will be reset to a factory default (often something like January 1, 2000, or the date the motherboard was manufactured). Your boot order will return to whatever the manufacturer set — usually the hard drive first, then USB, then CD/DVD.

If you had set a BIOS password, it will be cleared. If you had disabled certain hardware in the BIOS, it will be re-enabled. If you had overclocked your processor or changed RAM timing settings, those changes will be gone.

The first boot after a CMOS reset may take longer than usual as the computer re-detects all its hardware. This is normal. Once it finishes, subsequent boots should return to their normal speed.

Set your date and time again in Windows or macOS. If you had custom BIOS settings you want to restore, you'll need to enter the BIOS menu (usually by pressing Delete, F2, or F12 during startup — the key varies by manufacturer) and reconfigure them.

When to call for help instead of resetting CMOS

If your computer won't start at all — no lights, no fan noise, nothing — a CMOS reset won't help. That points to a power supply problem or a hardware failure, and you should check that the power cable is firmly connected and the outlet works before opening the case.

If your computer starts but immediately shuts down, or if it starts and then freezes, a CMOS reset may help if a bad BIOS setting is the cause. But if the problem persists after the reset, the issue is likely hardware-related — a failing hard drive, bad RAM, or a motherboard problem — and you'll need to troubleshoot further or seek repair.

If you're uncomfortable opening your computer case, or if your computer is still under warranty, contact the manufacturer or a repair shop before attempting this yourself. Opening the case can void some warranties, and static electricity can damage components if you're not careful.

Frequently Asked Questions

Will resetting CMOS erase my files or programs?

No. CMOS only stores hardware settings like boot order and date/time. Your operating system, files, programs, and all data on your hard drive remain unchanged. The reset affects only the BIOS firmware, not your storage.

What if I can't find the CMOS battery?

Check your motherboard's manual — it will show the exact location. If you don't have the manual, search online for your motherboard model number (printed on the board itself) plus "CMOS battery location". If your board has a jumper instead, the manual will show that too. Some very new or very old computers may use different methods.

Do I need to do anything special after the reset?

Set your date and time in Windows or macOS. If you had custom BIOS settings, you'll need to reconfigure them by entering the BIOS menu during startup. Otherwise, your computer should work normally. The first boot may be slower than usual.

How do I know if my BIOS is password-protected?

When you start your computer and press the key to enter BIOS (usually Delete or F2), you'll be prompted for a password. If you see a password prompt and don't know the password, a CMOS reset will clear it. After the reset, you can enter BIOS without a password.

Is it safe to reset CMOS myself?

It's safe if you take basic precautions: shut down and unplug the computer first, avoid touching other components, and work on a non-static surface. The CMOS battery and jumper are designed to be user-replaceable. If you're nervous, a repair technician can do it in a few minutes for a small fee.