BIOS - Basic Input Output System
The Basic Input Output System is a first software run by the computer, when the system is turned On. This software is usually stored in the Read Only Memory (ROM), located on the motherboard of a Computer.
The ROM is typically an Electrically erasable programmable read only memory (EEPROM). It allows the contents (bug fixes & upgrades) to be rewritten without removing the chip from the motherboard.
What does BIOS do
The main purpose of Basic Input Output System is to check all the Hardware component attached to the computer and to load the part of Operating System or other system programs to the RAM. The hardware devices may include : Keyboard, Mouse, Monitor, Hard Disk etc.