BIOS- Basic Input Output System: An Introduction
Starting Your System: How the BIOS loads the operating system
When you turn on your computer, several events occur automatically:
- The CPU "wakes up" and sends a message to activate the BIOS.
- The BIOS then runs a series of tests, called the POST for Power On Self Test,
to make sure the system devices are working correctly. In general, the BIOS:
- Initialises system hardware and chipset registers
- Initialises power management
- Tests RAM (Random Access Memory)
- Enables the keyboard
- Tests serial and parallel ports
- Initialises floppy disk drives and hard disk drive controllers
- Displays system summary information
- During POST, the BIOS compares the system configuration data obtained from POST with the
system information stored on a CMOS - Complementary Metal-Oxide Semiconductor
- memory chip located on the motherboard. (This CMOS chip, which is updated whenever new
system components are added, contains the latest information about system components.)
- After the POST tasks are completed, the BIOS looks for the boot program responsible for
loading the operating system. Usually, the BIOS looks on the floppy disk drive A: followed
by drive C:
- After being loaded into memory, the boot program then loads the system configuration
information (contained in the registry in a Windows environment) and device drivers.
- Finally, the operating system is loaded, and, if this is a Windows environment, the
programmes in the Start Up folder are executed.
Using the BIOS Setup program, you can modify BIOS settings and control special features
of your computer.
For example, you can select the sequence of drives the BIOS checks when loading
the operating system or turn the Numlock on or off.
The Setup program includes several menus for making changes and turning on or off
certain features. Before modifying any of these options, however, make sure you are
completely familiar with your system and the results of choosing various options.
It is possible to corrupt your hard disc data or disable
your computer completely by choosing the wrong settings.