What resetting CMOS actually does

Resetting CMOS clears the settings stored on a small battery-backed chip inside your computer. That chip holds information like your boot order, system time, and hardware settings — things your computer needs to know before Windows or Mac even starts. When you reset it, your computer forgets all those settings and goes back to factory defaults.

You might need to do this if your computer won't start, keeps showing the wrong time, or won't recognize a hard drive you just installed. It's also one of the few ways to regain access if you've forgotten a BIOS password (the password that locks your computer's deepest settings). Resetting CMOS is not the same as restarting your computer — it's a deeper reset that touches hardware-level memory.

Key Takeaways

  • CMOS is a small chip that stores your computer's hardware settings, and resetting it returns those settings to factory defaults.
  • The most common method is removing the CMOS battery from your motherboard for 10 to 30 seconds, then putting it back.
  • You will need to open your computer's case, so ground yourself first by touching a metal part of the case to avoid damaging components with static electricity.
  • After reset, you may need to re-enter settings like your boot order or system time, and your computer may take longer to start the first time.

When you actually need to reset CMOS

Most people never reset CMOS. You only need to if something specific goes wrong. The most common reasons are: your computer won't start and shows error messages about hardware detection, your BIOS password is locked and you can't access settings, your system time keeps resetting to the wrong date, or you've made changes in BIOS that broke something and you want to start over.

If your computer starts normally and you can log in, you almost certainly don't need to reset CMOS. If you're just having software problems — like Windows won't load or a program keeps crashing — resetting CMOS won't help. Those are operating system problems, not hardware settings problems.

How to reset CMOS by removing the battery

The battery method is the safest and most common way. First, shut down your computer completely and unplug the power cable from the wall. Wait 30 seconds. Then open your computer's case — usually by removing a side panel with a few screws. Look for a small coin-shaped battery on the motherboard, typically silver and about the size of a dime. It's usually labeled CR2032 or similar.

Before you touch anything inside, ground yourself by touching a bare metal part of the case frame. This prevents static electricity from damaging components. Gently push the battery holder clip to the side and lift the battery out. Leave it out for 10 to 30 seconds — longer doesn't hurt. Then press it back in until the clip snaps into place. Close the case, plug in the power cable, and start your computer.

Your computer may take longer to start the first time and may show a message saying settings were reset. This is normal. You may need to go into BIOS (usually by pressing Delete, F2, or F12 during startup — your computer will tell you which key) and set your boot order again if your computer doesn't start from the right drive.

Using the CMOS jumper if your computer has one

Some motherboards have a jumper — a small plastic clip on three metal pins — that can reset CMOS without removing the battery. Check your motherboard manual to see if yours has one. The manual will show you exactly which three pins to use and how long to move the jumper.

The process is similar: shut down, unplug, ground yourself, locate the jumper, move it to the reset pins for a few seconds, then move it back to its original position. This method is faster than removing the battery and carries less risk of dropping the battery or losing it inside the case. Not all motherboards have this feature, so check before you look for it.

What happens after you reset CMOS

Your computer will boot with all settings returned to what the manufacturer set them to. Your system time will probably be wrong — it might show a date from years ago. Your boot order may be reset, so if you have multiple drives, your computer might try to boot from the wrong one. Any custom settings you made in BIOS will be gone.

If you had a BIOS password set, it will be cleared. This is why resetting CMOS is sometimes used to bypass a forgotten BIOS password, though this only works if you have physical access to the computer and can open the case. If you made BIOS changes to fix a specific problem, you'll need to make those changes again after the reset.

Risks and things that can go wrong

The biggest risk is static electricity damage. If you touch components without grounding yourself first, you can permanently damage the motherboard. This is rare but possible. The second risk is physical damage — dropping the battery inside the case, or accidentally disconnecting a cable while the case is open. Work slowly and carefully, and take a photo of the inside of your case before you start so you can see what was connected where.

Another risk is that resetting CMOS won't actually fix your problem. If your computer won't start because of a failing hard drive or a software issue, clearing CMOS won't help. If you're not sure whether CMOS reset is the right fix, it's worth asking in a tech support forum or contacting the computer manufacturer first.

Alternatives if you can't or don't want to open the case

If you're uncomfortable opening your computer, some laptops and newer computers have a built-in way to reset CMOS through the BIOS menu itself. Look for an option called "Reset to Defaults" or "Load Optimized Defaults" in your BIOS settings. You can usually access BIOS by restarting your computer and pressing a specific key (Delete, F2, F10, or F12 — your computer will tell you which one during startup).

This method doesn't fully reset CMOS the way removing the battery does, but it clears most settings and solves many common problems. If this option doesn't work or isn't available, and you're not comfortable opening the case yourself, a computer repair shop can do it for you — it's a quick job and usually costs between $50 and $150.

Frequently Asked Questions

Will resetting CMOS delete my files or programs?

No. CMOS only stores hardware settings, not your files or programs. Everything on your hard drive stays exactly where it is. Your computer will still have all your documents, photos, and installed software after the reset.

How do I know if my computer has a CMOS battery?

Every desktop computer has one. Laptops usually have one too, though it may be harder to reach. If you're not sure, look up your specific computer model and motherboard online, or check the manual that came with it. A quick search for your model number plus "CMOS battery location" will usually show you a photo.

What if I can't find the CMOS battery?

Stop and don't guess. Take a photo of your motherboard and post it in a tech forum, or look up your exact motherboard model number (it's printed on the board) and search for its manual. The manual will show you exactly where the battery is. Poking around blindly risks damaging something.

Do I need to reset CMOS if I'm just upgrading my RAM or adding a new drive?

No. Your computer will detect new hardware automatically when you start it up. You only need to reset CMOS if the computer doesn't recognize the new hardware, or if you made changes in BIOS that caused problems.

Can I reset CMOS while the computer is plugged in?

You should always unplug the power cable first. Even when the computer is off, there's still a small amount of power flowing through the motherboard. Unplugging removes that power and makes the process safer.