What is BIOS (basic input/output system)? Part-II

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. 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.
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 read this port and data from keyboard goes to computer.
(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.
(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: