Computer Science XI

Components of a Digital Computer A computer system

Components of a Digital Computer A computer system is the integration of physical entities called hardware and non-physical entities called software. The hardware components include input devices, processor, storage devices and output devices. The software items are programs and operating aids (systems) so that the computer can process data. 

Functional Units of a Computer System

Computer system is a tool for solving problems. The hardware should be designed to operate as fast as possible. The software (system software) should be designed to minimize the amount of idle computer time and yet provide flexibility by means of controlling the operations. Basically any computer is supposed to carry out the following functions.

- Accept the data and program as input

- Store the data and program and retrieve as and when required.

- Process the data as per instructions given by the program and convert it into useful information

- Communicate the information as output Based on the functionalities of the computer, the hardware components can be classified into four main units, namely - Input Unit - Output Unit - Central Processing Unit - Memory Unit These units are interconnected by minute electrical wires to permit communication between them. This allows the computer to function as a system. The block diagram is shown below.

Fig. 3.1 : Functional Units of a Computer System

Input Unit

A computer uses input devices to accept the data and program. Input devices allow communication between the user and the computer. In modern computers keyboard, mouse, light pen, touch screen etc, are some of the input devices.

Output Unit

Similar to input devices, output devices have an interface between the computer and the user. These devices take machine coded output results from the processor and convert them into a form that can be used by human beings. In modern computers, monitors (display screens) and printers are the commonly used output devices

Central Processing Unit
Fig. 3.2. Central Processing Unit

CPU is the brain of any computer system. It is just like the human brain that takes all major decisions, makes all sorts of calculations and directs different parts of the computer function by activating and controlling the operation.

It consists of arithmetic and logic units, control unit and internal memory (registers).

The control unit of the CPU coordinates the action of the entire system. Programs (software) provide the CPU, a set of instruction to follow and perform a specific task. Between any two components of the computer system, there is a pathway called a bus which allows for the data transfer between them.

Control unit controls all the hardware operations, ie, those of input units, output units, memory unit and the processor.

The arithmetic and logic units in computers are capable of performing addition, subtraction, division and multiplication as well as some logical operations. The instructions and data are stored in the main memory so that the processor can directly fetch and execute them.

Memory Unit

In the main memory, the computer stores the program and data that are currently being used. In other words since the computers use the stored program concept, it is necessary to store the program and data in the main memory before processing. The main memory holds data and program only temporarily. Hence there is a need for storage devices to provide backup storage. They are called secondary storage devices or auxiliary memory devices. Secondary storage devices can hold more storage than main memory and is much less expensive.

Stored Program Concept

All modern computers use the stored program concept. This concept is known as the Von – Neumann concept due to the research paper published by the famous mathematician John Von Neuman. The essentials of the stored program concept are - the program and data are stored in a primary memory (main memory) - once a program is in memory, the computer can execute it automatically without manual intervention. - the control unit fetches and executes the instructions in sequence one by one. - an instruction can modify the contents of any location inThe stored program
concept is the basic operating principle for every computer.

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