What is BUS in computer architecture?

Bus is the path between components of computer or a collection of wire through which data is transmitted from one part of computer to another. The CPU has to be able to send various data, instructions, and information to all the devices and components inside the computer as well as to the different peripherals. These electronic pathways are nothing more than tiny wires that carry information, data and different signals throughout the computer from one component to the other components. This network of wires or electronic pathway is commonly known as the "System Bus".

The functions of Bus are:

(a) It carries information from one component to another.

(b) It carries data, address or control signal

The bus consists of three main parts

Control Bus

The control bus carries the control signal. The control signal is used for controlling and co-ordination of the various activities across the computer. It is generated from

the control unit within the CPU. The control bus is unidirectional from CPU to other components.

Address Bus

It is group of wires or lines that are used to transfer the address of memory or I/O devices. It is unidirectional, bits flow in one direction, from the processor to peripherals. The processor uses the address but to perform the function of identifying a peripheral or a memory location.

Data Bus

Data bus transfer data from one location to another across the computer. The meaningful data which is to be sent or retrieved from a device is placed on to these lines. CPU uses data bus to transfer data. These lines are bidirectional, data flow in both direction between the processor and memory and peripheral devices.

1. What do mean by computer architecture? Describe each functional components of computer architecture with typical diagram.

When referring to computers, architecture or computer architecture is the overall design and setup of the computer. This includes where connections and parts of the computer are to be placed, how each of components operate with each other, dimensions, etc.

It is a framework, functional description, design and implementation for various parts of computer.

The major hardware components of computer system are:

(a) Input Unit

(b) Processor

(c) Storage

(d) Output unit

(e) Memory

Figure: The basic block diagram of computer system.

Input Unit

The input unit is formed by the input devices attached to the computer. Input devices are used to interact with computer system or used to enter data and instructions to

the computer. Keyboard, Mouse, Scanner etc are some example of input devices.

The basic functions of input unit are:

• It accepts data and instruction from the outside world.

• It converts these data and instruction into computer understandable form.

• Supply the converted data to the computer system for further processing.

Central Processing Unit

CPU is a major component of any computer. It acts as heart and brain of computer, and performs all the processing related activities. It receives data and instructions from outside world, stores them temporarily, processes the data as per the instructions and sends the result to the outside world as information.

The CPU is combination of three components ALU, CU and Registers.

Arithmetic Logic Unit (ALU)

This is the area of CPU where various computing functions are performed. The main functions of ALU are as follows:

• It accepts operands from registers.

• It performs arithmetic and logical operations

• It returns results to register or a memory

Control Unit

The control unit provides the necessary timing and control signals to all the operations in the computer. It controls the flow of data between the CPU and memory and peripherals. The main funtions of control units are given below:

• It performs data processing operation

• It sends control signal to various parts of computer system for controlling

• It gives commands to input data from input unit to memory unit to ALU.

• It transforms result from ALU to memory unit to output unit.

• It gives command to store the data, instruction and program in memory.


Registers are the primary memory of computer system. They are mainly used to store data during the time of processing inside ALU.

The main function

• It holds the address of the active memory locations

• It holds the contents of the accessed (read/write) memory word.

• It holds the address of the next instruction to be executed.

• It holds the data to be operated upon, the intermediate results, and the results of processing.

• It hold the current instruction being executed.


Memory is the part of the computer system that is used to store data or instruction or program temporarily and permanently. Memory is the main storage unit in a computer. In simple terms, memory indicates the primary memory is the main storage unit in a computer. But, memory can be divided into two types primary or main memory and secondary or auxiliary memory.

Primary Memory

Alternatively referred to as internal memory, main memory, and primary memory, a primary storage device is a medium that holds memory for short periods of time while a computer is running. Although it has a much

lower access time and faster performance, it is also about two orders of magnitude more costly than secondary storage.

Random Access Memory (RAM) and cache are both examples of a primary storage device.

(This picture is only for students to


Secondary Memory

Secondary storage is any storage device designed to retain data and instructions (programs) in a relatively permanent form. Secondary storage is non-volatile that is stored data and instructions retain even if the power supply is cut off. It is also called as auxiliary memory or back-up memory.

Some example of secondary memory are Hard disk, Cd, DVD, Floppy disk, Magnetic tape etc.

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