BIOS and CMOS

 

Difference between BIOS and CMOS

In computer system, especially the motherboard, there are 2 key components –

• BIOS
  
  
• CMOS

In this article we will understand both the terminologies in detail. Also, how are they related and differences in their features/attributes.

What is BIOS?

BIOS implies to Basic Input Output System. It is a pre-installed program on windows based computer systems. BIOS is used to start the computers. BIOS is the first program installed in windows computers even before the operating system.

                                              

When we power on a computer, the CPU approaches the BIOS to find out all Input-Output devices and to look over if all hardware connections are properly functioning. BIOS is the one which loads the operating system in to the computer memory, thus completing the booting process.

BIOS is a part of the motherboard. It is stored in the permanent memory called non-volatile Read-only Memory or Erasable Programmable Read-only Memory (EPROM) chip or Flash Memory on the Motherboard of a computer. EPROM and Flash memory is used to upgrade the BIOS program as we can change the contents of EPROM and Flash memory.

Once the booting process is complete, the BIOS acts as an intercessor between the Input-Output devices and the CPU. All hardware details of the computer are known and managed by the BIOS. Whenever IO device changes, the information needs to be communicated to the BIOS.

What is CMOS?

CMOS technically stands for Complementary Metal-Oxide-Semiconductor. It is a physical portion of the motherboard. CMOS is a memory chip that holds configuration settings and is supported by the onboard battery called CMOS battery. CMOS battery is an associated component that offers power for Real Time Clock whether the computer is switched on or off.  Whenever changes are made in BIOS configuration all the changes are stored to CMOS chip.

The lifetime of a CMOS battery is around 10 Years. When the battery drains out of energy, CMOS is reset, loses all the custom settings and system clock is also reset. The CMOS returns to factory settings when the power is not coming from the battery. It’s a regular practice to remove the battery to recall CMOS settings if there is a configuration problem.

 

CMOS stores a small amount of data, usually 256 bytes. The information on the CMOS chip contains different types of disk drives that are installed, the current date and time of the system clock, and the computer’s boot sequence. 

 

PARAMETER	BIOS	CMOS
Full Form	Basic Input Output system	Complementary Metal Oxide Semiconductor
Memory Type	BIOS is nonvolatile	CMOS is volatile
Main Functionality	BIOS is a program which is used to initialize hardware during the booting process.	CMOS is a memory chip which stores the BIOS configuration settings
Upgradation	It can be upgraded by Flashing.	It can be changed trough CMOS setup
Location	BIOS is usually found in separate chipset called EPROM or Flash memory in motherboard.	CMOS is also a memory chip usually found in Southbridge.