We very often encounter the error called “CMOS checksum bad error”. Though it is quite an irritating error message, the remedies are quite easy for this error. Basically CMOS is Complementary metal oxide semiconductor and used in the integrated circuit design.

Now in computers CMOS has a specific and very important job. In CMOS memory the initial boot up data is stored. When the computer is getting started means boot up is in process, then the values are compared in the CMOS memory.

If the data are the same then the computer will start normally otherwise the above said message will be shown. Now there are several reasons for the values getting changed in the CMOS memory.

cmos checksum error image


As the problem is associated with motherboard and CMOS memory settings so platform can be any.


There are mainly three reasons for this error.

  1. The CMOS battery may have expired. In the motherboard there is a battery to keep the system clock running. Now if the battery is expired then the time and date settings will be changed and will not be updated.
  2. Computer is shut down improperly. Normally before power off the Operating system has to be shut down. Now if we remove the power supply before the shut down process then the error may occur on the next start.
  3. BIOS have been updated. This can be caused by any virus or by the user.


Depending upon the manufacturer there are different types of problems faced. For some computers there will be an error message on the initial boot up and the computer will get started normally.

For some other computers there will be an error message on the boot up and user will be asked to change the CMOS values to default. After that, the computer will get started normally.


Based upon the reason there are solutions for each of them.

  1. First of all, restart the computer again. If the error still persists then for the CMOS battery problem we can remove the battery and get it replaced by another one. You can do it by yourself but if not sure then better ask a person on the matter. If you are doing it by yourself then note down the voltage rating and size of battery to get a new one. After changing make the change in the CMOS settings also like the date and time.
  2. For BIOS update make sure that the settings are correct. It’s better to get settings to its default values. If the update is done by any virus then it’s better to get the computer scanned by a virus scanner. More importantly, always get your computer secured by a reliable antivirus program.

For a shut down problem make sure that the computer is getting shut down before power off. For different Operating Systems the process of shutting down is different. So always make sure to shut down the system before removing power supply.

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