BIOS-The BIOS (Basic Input-Output System) or UEFI Unified Extensible Firmware Interface is a software located on the motherboard ROM chipset, which handles all the startup routines necessary to get the computer running. 

In most PCs the BIOS will have 4 main functions:

POST - Test computer hardware insuring hardware is properly functioning before starting process of loading Operating System. Additional information on the POST can be found our POST / Beep Codes page.

Bootstrap Loader - Process of locating the operating system. If capable Operating system located BIOS will pass the control to it

BIOS - Software / Drivers which interfaces between the operating system and your hardware when running DOS or Windows you are using complete BIOS support

CMOS Setup - Configuration program. Which allows you to configure hardware settings including system settings such as computer passwords, time, and date?
Computer hardware are divided into 3 parts

BIOS manufacturers: American Megatrends, Phoenix, and Award

CMOS - Stores around 64K of Programming Short for complementary metal oxide semiconductor. Pronounced see-moss, CMOS is a widely used type of semiconductor. CMOS semiconductors use both NMOS (negative polarity) and PMOS (positive polarity) circuits. Since only one of the circuit types is on at any given time, CMOS chips require less power than chips using just one type of transistor. This makes them particularly attractive for use in battery-powered devices, such as portable computers. Personal computers also contain a small amount of battery-powered CMOS memory to hold the date, time, and system setup parameters. 

How to enter a typical CMOS setup: When PC boots up you will be told to press a key to get to setup:

Award (DEL)
Phoenix (F2)
American Megatrends (CTRL+ESC)
Others (F1, F10, ESC)

Note: some new motherboard designs allow access to the CMOS setup to be disabled through a motherboard jumper. If you cannot access the setup using the proper key commands stated above check your motherboard settings to see if the access has been disabled.

Special Thanks to American Megatrends, Award and Phoenix