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..