One of the most common uses of
is for the basic input/output system of your computer, commonly known
as the BIOS (pronounced "bye-ose"). On virtually every computer available,
the BIOS makes sure all the other chips, hard drives, ports and CPU function
Every desktop and
in common use today contains a
microprocessor as its central processing unit. The microprocessor is the
hardware component. To get its work done, the microprocessor executes
a set of instructions known as software (see
Microprocessors Work for details). You are probably very familiar with
two different types of software:
- The operating system - The
system provides a set of services for the applications running on your
computer, and it also provides the fundamental user interface for your
computer. Windows 98 and Linux are examples of operating systems. (See
Operating Systems Work for lots of details.)
- The applications - Applications are pieces of software that are
programmed to perform specific tasks. On your computer right now you
probably have a browser application, a word processing application, an
application and so on. You can also buy new applications and install them.
It turns out that the BIOS is the third type of software your computer
needs to operate successfully. In this edition of
you'll learn all about BIOS -- what it does, how to configure it and what to
do if your BIOS needs updating.
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,
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
ports, especially when the computer is booting.
- Managing a collection of settings for the
The BIOS is special software that interfaces the major hardware
components of your computer with the
system. It is usually stored on a
chip on the
motherboard, but sometimes the chip is another type of
BIOS uses Flash memory, a type of ROM.
When you turn on your computer, the BIOS does several things. This is its
- 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
Booting the Computer
Whenever you turn on your computer, the first thing you see is the BIOS
software doing its thing. On many machines, the BIOS displays text
describing things like the amount of memory installed in your computer, the
type of hard disk and so on. It turns out that, during this boot sequence,
the BIOS is doing a remarkable amount of work to get your computer ready to
run. This section briefly describes some of those activities for a typical
After checking the CMOS Setup and loading the interrupt handlers, the
BIOS determines whether the
is operational. Most video cards have a miniature BIOS of their own that
initializes the memory and graphics processor on the card. If they do not,
there is usually video driver information on another ROM on the motherboard
that the BIOS can load.
Next, the BIOS checks to see if this is a cold boot or a reboot.
It does this by checking the value at memory address 0000:0472. A value of
1234h indicates a reboot, and the BIOS skips the rest of POST. Anything else
is considered a cold boot.
If it is a cold boot, the BIOS verifies RAM by performing a read/write
test of each memory address. It checks the PS/2 ports or
USB ports for a
keyboard and a mouse. It looks for a peripheral component interconnect
(PCI) bus and, if it
finds one, checks all the PCI cards. If the BIOS finds any errors during the
POST, it will notify you by a series of beeps or a text message displayed on
the screen. An error at this point is almost always a hardware problem.
The BIOS then displays some details about your system. This typically
includes information about:
Any special drivers, such as the ones for small computer system
adapters, are loaded from the adapter, and the BIOS displays the
information. The BIOS then looks at the sequence of storage devices
identified as boot devices in the CMOS Setup. "Boot" is short for
"bootstrap," as in the old phrase, "Lift yourself up by your bootstraps."
Boot refers to the process of launching the
system. The BIOS will try to initiate the boot sequence from the first
device. If the BIOS does not find a device, it will try the next device in
the list. If it does not find the proper files on a device, the startup
process will halt. If you have ever left a floppy disk in the drive when you
restarted your computer, you have probably seen this message.
This is the message you get if a floppy disk is in
the drive when you restart your computer.
The BIOS has tried to boot the computer off of the floppy disk left in
the drive. Since it did not find the correct system files, it could not
continue. Of course, this is an easy fix. Simply pop out the disk and press
a key to continue.
In the previous list, you saw that the BIOS checks the CMOS Setup for custom
settings. Here's what you do to change those settings.
To enter the CMOS Setup, you must press a certain key or combination of
keys during the initial startup sequence. Most systems use "Esc,"
"Del," "F1," "F2," "Ctrl-Esc" or "Ctrl-Alt-Esc" to enter setup. There is
usually a line of text at the bottom of the display that tells you "Press
___ to Enter Setup."
Once you have entered setup, you will see a set of text screens with a
number of options. Some of these are standard, while others vary according
to the BIOS manufacturer. Common options include:
- System Time/Date - Set the system time and date
- Boot Sequence - The order that BIOS will try to load the
- Plug and Play - A standard for auto-detecting connected
devices; should be set to "Yes" if your computer and operating system both
- Mouse/Keyboard - "Enable Num Lock," "Enable the Keyboard,"
- Drive Configuration - Configure hard drives, CD-ROM and floppy
- Memory - Direct the BIOS to shadow to a specific memory address
- Security - Set a password for accessing the computer
- Power Management - Select whether to use power management, as
well as set the amount of time for standby and suspend
- Exit - Save your changes, discard your changes or restore
Be very careful when making changes to setup. Incorrect settings may keep
your computer from booting. When you are finished with your changes, you
should choose "Save Changes" and exit. The BIOS will then restart your
computer so that the new settings take effect.
The BIOS uses CMOS technology to save any changes made to the
computer's settings. With this technology, a small lithium or Ni-Cad
supply enough power to keep the data for years. In fact, some of the newer
chips have a 10-year, tiny lithium battery built right into the CMOS chip!
Updating Your BIOS
Occasionally, a computer will need to have its BIOS updated. This is
especially true of older machines. As new devices and standards arise, the
BIOS needs to change in order to understand the new hardware. Since the BIOS
is stored in some form of ROM, changing it is a bit harder than upgrading
most other types of software.
To change the BIOS itself, you'll probably need a special program from
the computer or BIOS manufacturer. Look at the BIOS revision and date
information displayed on system startup or check with your computer
manufacturer to find out what type of BIOS you have. Then go to the BIOS
manufacturer's Web site to see if an upgrade is available. Download the
upgrade and the utility program needed to install it. Sometimes the utility
and update are combined in a single file to download. Copy the program,
along with the BIOS update, onto a floppy disk. Restart your computer with
the floppy disk in the drive, and the program erases the old BIOS and writes
the new one. You can find a BIOS Wizard that will check your BIOS at
Major BIOS manufacturers include:
As with changes to the CMOS Setup, be careful when upgrading your BIOS.
Make sure you are upgrading to a version that is compatible with your
computer system. Otherwise, you could corrupt the BIOS, which means you
won't be able to boot your computer. If in doubt, check with your computer
manufacturer to be sure you need to upgrade.