CMOS full form is Complementary Metal–Oxide–Semiconductor. CMOS is the chip that powered by a battery to store and keep information such as time and date, and hardware settings in the computers.
CMOS checksum error
When you found your computer’s date and time always back behind every time you turn on the computer or your computer always asks to set up the configuration this indicates that the battery that powered the CMOS chip needs to be replaced. There is also a typical error message like CMOS checksum error.