2:
What BIOS Does The BIOS
software has a number of different roles, but its most
important role is to load the operating system. When you
turn on your computer and the microprocessor tries to
execute its first instruction, it has to get that
instruction from somewhere. It cannot get it from the
operating system because the operating system is located
on a hard disk, and the microprocessor cannot get to it
without some instructions that tell it how. The BIOS
provides those instructions. Some of 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 - For example, SCSI and graphics
cards often have their own BIOS chips.
- Providing a set of low-level routines that the
operating system uses to interface to different
hardware devices - It is these routines that give the
BIOS its name. They manage things like the keyboard, the
screen, and the serial,
and parallel ports, especially
when the computer is booting.
- Managing a collection of settings for the hard disks, clock, etc.
The BIOS is special software that interfaces the
major hardware components of your computer with the operating system. It is usually
stored on a Flash memory chip on
the motherboard but sometimes
the chip is another type of
ROM.
BIOS uses Flash memory, a type
of
ROM. |
When you turn on your computer, the BIOS does several
things. This is its usual sequence:
- Check the CMOS Setup for custom settings
- Load the interrupt handlers and device drivers
- Initialize registers and power management
- Perform the power-on self-test (POST)
- Display system settings
- Determine which devices are bootable
- 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. We will
talk more about these settings later.
Interrupt handlers are small pieces of
software that act as translators between the hardware
components and the operating system. For example, when
you press a key on your keyboard, the signal is sent to
the keyboard interrupt handler, which tells the CPU what
it is and passes it on to 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.
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