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CMOS Checksum Bad Error

We very often encounter the error called “CMOS checksum bad error”. Though it is quite an irritating error message but the remedies are quite easy for this error. Basically CMOS is Complementary metal oxide semiconductor and used in the integrated circuit design. Now in computer CMOS has a specific and very important job. In CMOS memory the initial boot up data are stored. When computer is getting started means boot up is in process, then the values are compared in the CMOS memory.

If the data are same then 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.



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 power supply before shut down process then the error may occur on next start.
  3. BIOS have been updated. This can be caused by any virus or by the user.


Depending upon manufacturer there are different types of problem faced. For some computer there will be a error message on the initial boot up and the computer will get started normally. For some other computer there will be an error message on the boot up and user will be asked to change the CMOS values to default. After that computer will get started normally.


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

  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 shut down problem make sure that 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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