Clear CMOS Settings

In this video from ITFreeTraining, I will look at how to clear the CMOS settings on a computer. When changes are made in the BIOS or UEFI, these settings are stored in the CMOS. This video will look at how to clear these settings which will return the computer back to its factory defaults.

BIOS and CMOS
0:19 Before I start, I will first look at how the BIOS and the CMOS work. This will give you a better understanding of what happens when the settings are cleared. In this video, I will only refer to BIOS, but if you have a computer with a UEFI chip on it, the principal is the same and the procedures are also the same.

The BIOS is a small chip on the motherboard. This chip contains a small amount of code and when the computer is first switched on, this code tests the hardware and starts the computer.

The BIOS also contains setup software that allows configuration changes to be made to the computer. These configuration changes need to be stored somewhere, but cannot be stored in the BIOS because it is read only.

In the early days of computing, this configuration was stored in a chip called the CMOS. CMOS stands for complementary metal-oxide semiconductor. Nowadays, motherboards do not have a CMOS chip, but instead the configuration is stored in the South Bridge.

The size of this storage varies, but in modern motherboards it is around 64 kilobytes. The average computer may only require 100 bytes of storage depending on what options you configure. This storage is traditionally volatile, meaning that when the power to the computer is switched off everything in memory will be lost.

Since this data is the configuration for the computer, you need the configuration to be available even if the computer does not have power for long periods. To do this, the motherboard will have a battery installed. This battery keeps the memory powered and thus data will not be lost between reboots.

You may be thinking, why not use flash RAM as it is non-volatile and thus keeps its values between power losses? A lot of modern motherboards use flash RAM and thus do not require power to keep their settings. Even if flash RAM is being used, the settings are still referred to as CMOS because administrators are so used to calling it by that name. If we are making the move to flash RAM, the question arises, do we still need the battery?

The battery is still found on modern motherboards because it is used to power the clock. The clock is referred to as the real time clock or RTC. The battery allows the clock on the motherboard to function even when the computer is not powered. This allows the computer to accurately keep track of the time, including the current date even if the computer is not connected to the power for a long period of time.

Now that we understand how the settings are saved, what happens if you make a change to CMOS on your computer and the computer becomes unbootable? The most common time this occurs is when a password has been configured and no one knows what that password is. When something like this occurs, you need a way of clearing the CMOS settings.

Clearing CMOS
3:13 1_Bullet12_Jumper

To clear the CMOS settings, which will set the motherboard back to factory defaults, there is a jumper on the motherboard. To clear the settings, move the jumper to the second position and start the computer up.

Clearing CMOS
3:25 If you have trouble locating the jumper, refer to the motherboard manual for its location. It is usually located next to the BIOS chip. There will usually be some printed text next to it help you find it. Usually it will have the letters CLRTC which stand for Clear Real Time Clock. Essentially you reset all the settings and also reset the real time clock. If you have a computer that you keep having to set the time and date on, chances are the battery on the motherboard is dead.

I will now have a look at how to reset the CMOS and also have a look at the effect removing the battery will have on the computer.

Demonstration
4:05 First, I will start the computer and press the delete key to enter the setup. Once in the setup, notice that the date is currently set correctly. Once I reset the CMOS setting, we will notice that the time and date will not be correct.

References
“The Official CompTIA A+ Core Study Guide (Exam 220-1001)” Chapter 3 Position 6115 - 6269“CompTIA A+ Certification Exam Guide Tenth Edition” pages 125 - 126

Credits

[SDN_]

You explained each information very clear and understandable. Thank you so much. Thumbs up 👍

[fareenjatoi]

A perfect example of how a detailed informative video should be.

[johntodd]

This is the best video out there, , hands down. Ok, I have 3 long beeps 2 short beeps. I have a cmos reset button on the motherboard. Does this work as the jumpers? I unplugged it, pulled the batter for 5 minutes and pushed the reset button on the motherboard and voila. This is a great video. Liked and subscribed.

[tkbanque]

unbelievable, this make it clear about CMOS, thank you

[faizalali]

I have a asus motherboard but I followed everything you said and it's working! Thank you.

[fareenjatoi]

Keep it up !
Your channel really helps me so much.

[MaheshKumar-jiq]

Hi, great video. Sorry, I have a quick question: in order to reset the CMOS, do you keep the jumper cable connected to the extreme right side pins or after a while do you reposition them to the left?

[WinTheWarWithin]

Great video! I learnt a lot. 👍

Will this work with Intel NUC Skull Canyon? Intel NUC Mini PC i7-8705G with RX Vega M GL Graphics

My PC failed a BIOS update last night and I'm losing sleep. Lol.

[Gaurav_c]

I have the same bios as yours but it is stuck on the page where it says phoenix bios . It is stuck at memory testing and the computer is not booting can you help?

[richardcirelli]

wow big taking PC fundamental class and instructor dose not really show step by this video is great need more out there that walk you through a step by step.thanks

[fareenjatoi]

Great video, it takes lots of courage and efforts to make such contents.
Thankyou

[kitsune]

new to debugging motherboard codes. I have a 'd3' code on a asus board, im going to try this since it sounds like a great place to start :)

[saralanzuise]

I love you explain things! makes easier for everyone. Thanks a lot for the valuable channel.

[NikonErik]

My procedure it critically different than in this video! My ASUS Motherboard manual has me turn off and unplug the power cord before moving the jumper. Wait 5-10 seconds. Move the jumper back, then plug in the PC and turn it on.

[geraldahlstrom]

Good video, however must I flash a new bios to accomplish the act?

[giaptheson]

Please note that without CMOS battery, when the computer shuts off, all BIOS settings will be returned to factory defaults, leading to the error message every time the computer turns on stating that you have to set date and time.

[wlmrcruz]

Will this method clear the admin password in the bios? thank you in advance

[NickB-hyfe]

Od if I take the main battery out also have to take the CMOS battery out or will the main battery be okay

[KeiffyGames]

Hey man quick question? I just upgraded from the Ryzen 5 3600 to the 3700x, and everything seems to be fine and working. I click on SYSTEM and it shows I now have the 3700x as my cpu, but when I try to enable All cores and when I go into the Task manager, still says 3700x but under CPU its still showing 6 cores and 12 threads from my 3600? Any ideas as to why this is, and how to fix it? Please Help. And Thanks

[OutlawedPoet]

This was a great video. Got a problem though. I have the BIOSTAR A320MH motherboard. A while ago, I accidently increased the CPU clock too high and it wouldn't boot. After placing the jumper on the second and third pins, the settings were reset and the computer worked fine. However, after clearing everything, I tried to put the jumper back onto the first and second pin (which is what BIOSTAR says you should do) and the computer would not boot. Put the jumper cap back to the second and third slot, and the CMOS was cleared, and it booted again. Do you know why this is? The first and second pins are the "normal" ones according to the motherboard label FYI. Weirdly enough though, the picture they use for the overview page has the jumper on the second and third pins.