CMOS stands for Complementary Metal-Oxide-Semiconductor and refers to a small bit of memory on your motherboard that is used to save your BIOS settings. This allows your BIOS settings to be stored directly on your motherboard, so they can always be accessed, even without any added storage or any operating system on your PC.

Resetting the CMOS likely won't be your first port of call when you experience issues with your PC. However, it is an important step in the troubleshooting process and something that is generally easy enough to do that everyone should know how to do it. Whether you are experiencing freezing on startup, issues after a BIOS settings change, or something just doesn't feel right after installing a new kit of RAM, resetting your CMOS can sometimes be the easiest of fixes.

First things first

Let's not jump the gun

Before we look into resetting the CMOS, there are a couple of things we can try. The first thing you should do, depending on the issue at hand, is make sure everything is installed correctly. If you're having issues getting a display, check that your RAM, GPU, and monitor are all connected properly. If your PC is randomly turning off, check that your power supply is plugged in correctly to the main socket and on the motherboard. You may also want to check your CPU temps, since your PC may automatically shut down as they get too high.

If you have just installed some new hardware on your PC, and everything was fine before, it could be worth checking for BIOS and driver updates. While a lot of things are plug-and-play these days, sometimes they do need a bit of an update to ensure they are working as intended.

Always switch your power supply off (where applicable) and unplug the power cable directly from the unit itself before resetting the CMOS.

Using the motherboard's reset buttons

Rear I/O and main header area

The easiest way to reset the CMOS is if your motherboard has CMOS reset buttons. Unfortunately, not all motherboards do, but it is something we are seeing more of lately. There are two places these buttons can be located. The first is on the rear I/O where you will plug in all your peripherals, monitors, etc. The second is somewhere on the motherboard itself, normally either near the 24-pin power connector or towards the bottom with all the jumpers and headers.

Using these buttons to reset CMOS is a simple process. As mentioned above, disconnect your PSU, then hold down the CMOS reset button for 5–10 seconds, and you should be good to go. Normally, when you go to turn your PC on after this, it will say some settings have been changed and ask you to enter the BIOS to verify everything. If you see this, you will know it worked correctly.

Removing the CMOS battery

Yup, take it right out

Almost as easy as hitting the reset button, but not quite. Almost all motherboards have a small battery on them. It's normally a flat CR2032, but not always. Once you find it, you will notice there is a small metal tab on one side. If you push that metal tab in, it will release the battery and remove power from the motherboard.

There's always speculation about how long to remove the battery. In all the years I have been working on PCs, I find 30–60 seconds is more than enough. If your motherboard is still connected to a power button of some sort, you can press this for 10–15 seconds as well to help make sure all the power is drained from the motherboard. Again, make sure the PSU is disconnected from the wall socket before doing this.

Using the motherboard jumper pins

Old school method, but still worth knowing

One of the original and probably most annoying ways to clear your CMOS is by jumping a pair of pins on the motherboard. The reason this is annoying is they can be located almost anywhere on the motherboard and sometimes aren't always clearly labeled. Once you find them, things get a bit easier.

To reset the CMOS this way, you need to "jump" the pins, or connect them somehow. A lot of older motherboards in the past used to come with a little plastic jumper tool for this purpose. However, you can use anything metal to connect the pins, such as a pen, screwdriver, or even a butter knife. You will need to make sure to be careful not to scratch the motherboard and, as always, make sure the PSU is disconnected from the main socket.

Why would I need to reset my CMOS?

The main reason to reset your CMOS is if something just isn't working quite right. It sounds silly, but this can make troubleshooting your PC much easier when it is facing issues and, in some cases, can fix the issue at hand. Here are some examples of things that could cause you to want to reset your CMOS.

• Virus: There are some nasty viruses out there, and sometimes they can change your PC settings, causing major issues. Depending on the issue you are facing, if using an antivirus software hasn't resolved your issues, resetting your CMOS may be the key.
• Failed overclock: If you have recently tried to overclock your CPU or RAM and things just don't seem quite right, resetting the CMOS may help. It will put all your BIOS settings for your CPU and RAM back to default and should allow you to start again from the beginning.
• Black screen on boot up: This could be caused by a bad overclock or many other things. Double-check if your RAM is installed properly and that your GPU and monitor are also connected properly. If everything looks fine, you may need to reset the CMOS to get back to the default BIOS settings again.
• Random blue screen of death: A lot of times this can be caused by faulty RAM, but that is not always the case. Sometimes, resetting the CMOS can help fix any hiccups in the BIOS settings and alleviate any Blue Screen of Death (BSOD).
• Installing new hardware: In most cases, you shouldn't need to reset the CMOS before installing new hardware. However, if you are upgrading your CPU and/or RAM, and have changed some BIOS settings, it may be easiest to just do a CMOS reset to get things back to default.

Sometimes, there is no rhyme or reason as to why computers start acting up. Having the right knowledge to try and fix these issues when they arise, though, is a whole different story. Most people use a computer either in their home or their workplace on almost a daily basis. Being able to do a small bit of troubleshooting before calling in an IT expert is a great way to sort out issues as quickly as possible.