The first software to run on your computer when you switched on the computer system is BIOS. BIOS is pre-installed when the computer is purchased. It reads the BIOS chip for instruction on what to do. The software programs installed on your system that you use daily, such as- browser, media player, office suite, etc. are high level software because they directly interacts with the operating system not to bare hardware. BIOS is low level software because it directly controls and communicates to the hardware components of the computer system. BIOS provide a number of services that allows users and higher level software to configure the settings for a computer system.
The four main functions of the BIOS are-
Power - On Self Test (POST) - It ensure that all the necessary hardware components are attached to the computer before it starts. After the POST, the major components (as- keyboard, Mouse, system memory, IDE drives) are initialized and made functional.
Bootstrap Loader- Locate the operating system and made functional. If a capable operating system is located, the BIOS will pass control to it. The BIOS looks in predetermined (it is usually decided by the computer manufacturer) locations for a bootable operating system. The Common places are- the CD-ROM drive, DVD drive, Pen drive and finally the hard disk drive.
BIOS drivers- Low-level drivers that give the computer basic operational control over your computer's hardware.
BIOS or CMOS Setup- Configuration program that allows you to configure hardware settings including system settings such as computer passwords, date, time and etc.