When you turn your computer on, a sequence of commands are automatically executed:

1. Information about your system configuration is loaded from the BIOS into main memory and chipset registers.

2. The BIOS executes a set of system diagnostics known as POST tests (Power On Self Test) to confirm that the various components of your system are working properly. During bootup, the BIOS will: check floppy and hard disk drives; initialize chipset registers and system hardware; check memory size and test memory; setup power management; check I/O ports; display system configuration information on the screen; check system configuration information stored in CMOS (CMOS (complementary metal-oxide semiconductor)
A semiconductor technology that uses less power and generates less heat (enabling higher circuit density) than bipolar semiconductor technologies. (another name for a BIOS chip).

3. After POST, the BIOS hands control of the system over to the operating system. It searches for command lines on the hard drive or floppy that load device drivers and the operating system. After the command lines are executed the operating system loads and the BIOS jumps in the back seat.

For more informatiom like this visit our extensive BIOS FAQs page.