The BIOS software has most important role is to load the operating system. Such as when you turn on your computer and the microprocessor tries to execute its first instruction, it has to get that instruction from somewhere. The BIOS provides those instructions. The other common tasks that the BIOS performs include:
• A power-on self-test (POST) for all of the different hardware components in the system to make sure everything is working properly
• Activating other BIOS chips on different cards installed in the computer
• Providing a set of low-level routines that the operating system uses to interface to different hardware devices. Such as the keyboard, the screen, and the serial and parallel ports etc.
• Managing a collection of settings for the hard disks, clock, etc.
The BIOS is special software that interfaces. It is usually stored on a Flash memory chip on the motherboard, but sometimes the chip is another type of ROM.
When you turn on your computer, the BIOS does several things. This is its usual sequence:
1. Check the CMOS Setup for custom settings
2. Load the interrupt handlers and device drivers
3. Initialize registers and power management
4. Perform the power-on self-test (POST)
5. Display system settings
6. Determine which devices are bootable
7. Initiate the bootstrap sequence
The first thing the BIOS does is check the information stored in a tiny (64 bytes) amount of RAM located on a complementary metal oxide semiconductor (CMOS) chip. The CMOS Setup provides detailed information particular to your system and can be altered as your system changes. The BIOS uses this information to modify or supplement its default programming as needed.
Interrupt handlers are small pieces of software that act as translators between the hardware components and the operating system.The device drivers are other pieces of software that identify the base hardware components such as keyboard, mouse, hard drive and floppy drive. Since the BIOS is constantly intercepting signals to and from the hardware, it is usually copied, or shadowed, into RAM to run faster.