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Difference Between CMOS and BIOS


BIOS (Basic Input Output System) and CMOS (Complementary Metal Oxide Semiconductor) are two terms that are used interchangeably in relation to computer technology. This is because they are very closely related to each other. In actuality, these two are nothing alike. BIOS is a type of software that manages the computer hardware when a computer boots-up. It is more like a primitive operating system that initializes all the resources needed by the true operating system. On the other hand, CMOS is a type of integrated circuit. The reason why the two seem so intertwined is the usage of a CMOS chip to store the information needed by the BIOS. These are the settings you change by accessing a menu during boot-up; commonly by pressing F2.

One of the main reasons why CMOS was chosen is because of its very low energy consumption. The CMOS chip is constantly powered and when the system is off, a CR-2032 battery takes over the job to keep the information stored within. Once power is lost, the settings are also lost. On the other hand, the BIOS doesn’t need to be constantly powered as the code is stored in non-volatile memory. It also runs for only a short period of time before handing control over to the true operating system.

Another difference between CMOS and BIOS is their importance. While the contents of CMOS are important, losing it is not really disastrous for the entire system. It can easily be restored by going to the menu during boot-up. The BIOS code is very important as without it, the computer would not be able to boot. To repair, the chip containing the BIOS needs to be removed and reprogrammed. There are many safeguards to prevent the corruption of the BIOS; including multiple restrictions to prevent accidental corruption and employing multiple chips containing the same BIOS for disaster recovery.

The term CMOS has stuck even though CMOS is no longer employed for quite some time. Flash memory has become the medium of choice for storage. On the other hand, the BIOS is still in wide use in many modern computers; although, BIOS is expected to be replaced with UEFI in the near future.


1. CMOS is type of chip while BIOS is a simple operating system
2. CMOS should always be powered but not the BIOS
3. CMOS is not critical while BIOS is
4. CMOS is no longer in use while BIOS still is

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