The BIOS (Basic Input Output System) can be defined as a set of built in software routines. The BIOS controls many of the most important function of the PC, like how it interprets keystrokes, communication through the computer ports etc. it also has the job of testing the computer every time it is turned on.

In fact it is responsible for the allocation of system resources. Simply stated the BIOS serves as a link between the hardware and software of your computer.

The BIOS cannot be classified as either software or hardware, it is both. Like software, the BIOS is a set of instructions to the computer’s processor. The fact that it is sometimes codes onto the chip gives it the hardware classification. In fact a correct term for something like the BIOS is Firmware. The BIOS code of most PCs has a wide variety of functions to take care of.

Typically, it comprises of program routines that test the computers. It also does the task of letting software take over control of the computer’s hardware, so that the program can run more smoothly.

BIOS also include a complete system for determining the peripherals and cards that we have installed and ensuring that they do not conflict in their requests for input/ output ports and memory assignment. In most cases the first thing the BIOS tells the microprocessor to do is run through all the hardware of the system like keyboard, mouse etc and to test it they are working properly followed by the boot up process.

During the boot process the BIOS code instructs the microprocessor to go to a particular section of code, that tells the chip how to read the first sector of your hard disk. The program code then takes over from the BIOS and tells the processor how to load the operating system to get your machine up and running.


Bus Architecture


The bus is a medium used to transfer data and controls from one part to other part of computers. There are mainly three types of bus:

  • Data bus: A bus which carries a word to or from memory is known as data bus.
  • Address bus: The address bus carries memory address. The width of the address bus equal to the number of bits in the MAR (Memory Address Register) of the memory.
  • Control bus: The control bus carries the control signals between the units of computers. For instance, if the processor has to send READ and WRITE commands to memory, START command to I/O units, etc, such signals are carried by a control bus.

Functions of BUS:

(i) Carries information from one place to another.

(ii) It may carry data, address or instructions.

(iii) One component interacts with other through bus.

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