BIOS stands for Basic Input Output System.
System Bios is a chip located on all the mother board which which contains a set of instructions how your system should boot and operate.

There are four main types of which BIOS performs:
1) POST-- it test the computer hardware and confirms that there is no error in the hardware before the operating system is loaded
2)Bootstrap loader--Locates the operating system and if it is found gives all the control to the operating system
3)BIOS Driver- here the drivers give basic operational control to the hardware
4) BIOS setup--Configuration program that allows you to configure hardware settings including the system settings..
Bios are the files which control processes like your computer clock and background processes when you see the windows when starting your computer its because of bios