A BIOS
(Basic Input/Output System) Short for ROM BIOS, or System
BIOS is an electronic set of instructions that a computer uses to
successfully start operating. The BIOS is located on a chip inside of the
computer and is designed in a way that protects it from disk failure. The main
function of the BIOS is to give instructions for the Power-On Self Test (POST).
This self test ensures that the computer has all of the necessary
parts and functionality needed to successfully start itself, such as use of
memory, a keyboard and other parts. If errors are detected during the test, the
BIOS instructs the computer to give a code that reveals the problem. Error
codes are typically a series of beeps heard shortly after startup.
The BIOS also works to give the computer basic information about
how to interact with some critical components, such as drives and memory that
it will need to load the operating system. Once the basic instructions have
been loaded and the self-test has been passed, the computer can proceed with
loading the operating system from one of the attached drives. Computer users
can often make certain adjustments to the BIOS through a configuration screen
on the computer. The setup screen is typically accessed with a special key
sequence during the first moments of startup. This setup screen often allows
users to change the order in which drives are accessed during startup and
control the functionality of a number of critical devices. Features vary among
individual BIOS versions.
We can also use flash-memory cards to hold BIOS information. This
allows users to update the BIOS version on computers after a vendor releases an
update. This system was designed to solve problems with the original BIOS or to
add new functionality. Users can periodically check for updated BIOS versions,
as some vendors release a dozen or more updates over the course of a product's
lifetime. Mother board (System) BIOS, Video adapter firmware (BIOS), Drive
controller firmware (BIOS), Modem Card firmware (BIOS),Network adapter board.
BIOS, SCSI adapter BIOS. The mother board BIOS provides routines to support
motherboard features. BIOS ROM chips for major sub systems of computer such as
video and drive control must also be included.
Actually BIOS can be placed in between the computer and external
devices as its name tells it is used for reading the keystroke, displaying
values on screen, Reading and writing to and from floppy and hard disks etc.
The keyboard is assigned the port number 60, which is known to
BIOS. BIOS reads this port and data from keyboard goes to computer.
FUNCTIONS OF BIOS
BIOS a boot firmware program on a PC which controls the computer
from the time you start It up until the operating system takes over. When you
turn on a PC, the BIOS first conduct a basic hardware check, called a Power-On
Self Test (POST), to determine whether all of the attachments are present and
working. Then it loads the operating system into your computer's random access
memory, or RAM. The BIOS also manages data flow between the computer's
operating system and attached devices such as the hard disk, video card,
keyboard, mouse, and printer. The BIOS stores the date, the time, and your
system configuration information in a battery-powered, non-volatile memory
chip, called a CMOS (Complementary Metal Oxide Semiconductor) after its
manufacturing process. The main functions of the BIOS are:
(i) BIOS power on self Test (POST)
(ii) Bootstrap loader
(iii) BIOS Setup utility program
(iv) System service routines
(i) BIOS Power on Self Test (POST): While booting the system,
BIOS first performs POST. It is a built-in diagnostic program that checks
hardware to ensure that everything is present and is working properly. Then
additional tests are done during booting. The POST takes very less time to run
and if there is no problem, it is difficult to notice that it is running.
Actually the monitor even had not activated to see the problem (if there), so
speaker is used. When a PC is turned on, there are beeping sounds and if there
is some problem in machine, system stopped without booting up. These beep
patterns depends on the maker of BIOS and used to diagnose many hardware
problems of Pc. As the POST tests all important components of system, POST boot
errors are fatal. BIOS send the detail of problems to special I/O address
(usually 80h). A special debugging card is put to ISA slot to accept debugging
codes that BIOS sends to it. The place where POST stops and find a problem can
be seen by displaying the codes from card.
(ii) Bootstrap Loader: To boot the operating system. The BIOS
contains a program known as bootstrap loader whose responsibility is to search
and start the operating system boot program. Then the boot program of operating
system controls the computer system and boots the operating system. The boot
sequences for Award BIOS software are;
(i) Test the CPU
(ii) Initialize support chips
(iii) Initialize the keyboard
(iv) ROM BIOS test
(v) CMOS RAM test
(vi) Memory test
(vii) Cache initialization
(viii) Initialize the vector table
(ix) CMOS RAM check sum
(x) Keyboard initialization
(xi) Video circuit test
(xii) Video memory test
(xiii) DMA Controller test
(xiv) PIC tests
(xv) EISA mode test
(xvi) Enable EISA slots
(xvii) Check memory size
(xviii) Memory test
(xix) Check EISA memory
(xx) Mouse initialization
(xxi) Cache initialization
(xxii) Shadow RAM setup
(xxiii) Floppy test
(xxiv) Hard drive test
(xxv) Serial/parallel port test
(xxvi) Initialize math coprocessor
(xxvii) Boot speed
(xxviii) POST loop
(xxix) Security/Password information
(xxx) Write to CMOS RAM
(xxxi) Initialize adapter ROM
(xxxii) Set up the time
(xxxiii) Boot the system and control given to INT 19 boot loader.
(iii) BIOS Setup Utility Program: A non volatile memory (NVRAM)
is used to store information about the computer system. During installation of
a system, the user run BIOS setup program and enter the correct parameters. The
settings of memory, disk types and other settings are stored in NVRAM and not
in BIOS chip itself. To construct NVRAM, the material required is CMOS
(Complementary metal oxide semiconductor). These CMOS chips are very efficient
storage devices as they store and maintain data on very low values of current.
The system's configurations therefore are also termed as CMOS settings, which
we can set using BIOS set up program. The BIOS reads the parameters from CMOS
RAM as and when required.
CMOS settings can be maintained by battery backup either by using
capacitor or by a battery built into NVRAM chip. This chip also has system
clock. If there is no battery, the setting remains for short period of time and
we need to reset the system. With it there is loss of BIOS password which
protects BIOS set up program.
To clear the CMOS RAM contents, two methods used are
(i) By using clear CMOS jumper.
(ii) By holding down enter key during booting of the system.
For Pentium III motherboards, different set ups are there in AMI
BIOS. These are:
• Standard CMOS Setup: It is used to set time date, hard disk type, type of floppy drive,
type of monitor and keyboard.
Advanced CMOS Setup: It is used to set typematic rate and delay, above 1 MB memory
test, memory test tick sound, Hil < Del> message display, system boot up
sequence etc.
• Advanced Chipset Setup: It is used to set features of chipset.
• Power Management Setup: It is used to control power conservation
options.
• PCI/Plug and Play Setup: It is used to set options of PCI bus and that of
plug and play devices.
• Peripherals Setup: It is used to control options related to I/O controllers.
• CPU Configuration Setup: This setup is used to select the types of CPU
installed in the motherboard. In AMI BIOS, the settings are auto as it
automatically finds out the type of CPU in the computer system.
• System Service Routines: The BIOS provides various software routines
(subprograms) that can be called by higher-level software such, as DOS,
Windows, or their applications, to perform different tasks. Virtually every
task that involves accessing the system hardware has traditionally been
controlled using one or more of the BIOS programs (although many newer
operating systems now bypass the BIOS for improved performance). This includes
actions like reading and writing from the hard disk, processing information
received from devices, etc.
BIOS services are accessed using software interrupts, which are
similar to the hardware interrupts except that they are generated inside the
processor by programs instead of being generated outside the processor by
hardware devices. One thing that this use of interrupts does is to allow access
to the BIOS without knowing where in memory each routine is located.
Normally, to call a software routine you need to know its address.
With interrupts, a table called an interrupt vector table is used that
bypasses this problem. When the system is started up, the BIOS puts addresses into
this table that represent where its routines are located for each interrupt it
responds to. Then, when DOS or an application wants to use a BIOS routine, it
generates a software interrupt. The system processes the interrupt, looks up
the value in the table, and jumps to the BIOS routine automatically. DOS itself
and application programs can also use this interrupt vector table.
Post a Comment