What is a Computer?

A Computer is an electronic machine with some mechanical facilities and is used mainly for data processing. It performs arithmetical and logical operations on the input data and gives the desired output. But in between the input and output, there is a step called processing which is done by the computer and processing methods on setups are provided by the users by a logical instruction known as program.



Functional Units of a computer
A computer is also a system because it is a group of integrated parts which are used to solve any problem by executing a suitable program.
Basically, there three types of functional unit of computer.
(1) Input/Output unit
(2) CPU
(3) Memory

Input/Output unit
A computer uses input devices for data entry purposes. Some input devices allow direct communication between the user and the computer. Devices connected directly to a computer are said to be on-line devices; mouse, light pen, touch screen etc. are all on-line devices.
Similar to input devices, output devices have an inter face between the user and the computer. These devices take machine coded output results from the processor and convert them into a form that can be used by human beings.

CPU(Central Processing Unit)
Central processing unit is the heart of any computer system. It consists of primary memory unit, arithmetic and logic unit and control unit.

Control Unit (CU):-Central unit controls all the hardware operations, i.e., those of output units, storage and of the processor itself. It fetches the requisite from main storage, stores it in a number of special registers, interprets the registers, interprets the instructions and follows the instructions to be executed by giving signals (or commands) to the appropriate hardware devices.

Arithmetic and Logic Unit (ALU):- The arithmetic and units in computers are capable of performing addition, subtraction, division a Subtraction, division and multiplication as well as some logical operations. The ALU has a number of selection lines to select a particular micro-operation in the unit.
Memory:-The memory or storage section of the computer consists of the devices used to store the in formation that would be used during the computations. The memory section of the computer is also used to hold both intermediate and final results as the computer proceeds through the program.
Memory can be divided into two categories-Primary Memory and Secondary Memory. Details of Primary Memory or Main Memory are as follows.
(A) RAM (Random Access Memory); and
(B) ROM (Read Only Memory).

Characteristics of a Computer
A computer is a fast and accurate electronic system that is designed to accept and store input data, process them and produce output results using the instructions of a stored program.
Speed and Accuracy :-Computer executes one instruction at a time. It can add and subtract numbers, compare characters to determine string matching and copy numbers and characters. There is nothing new in these operations.
In additions to their high speeds, computers have high accuracies as well. The circuits in a computer have electronic parts which do not have wear and tear.
Processing Capabilities:- Computer processing involves manipulating the symbols that represent things required by the user. People have been using characters, numbers and other symbols and computer processing simplifies this human task by providing the necessary speed and accuracy.
Data and Information:-Data are represented by symbols. After processing the data, information is produced. Thus information is data arranged in an order that would be useful to the user.
Data processing consists of three basic activities.
(1) Capturing the input data
(2) Manipulating the data and
(3) Handling the output results.

Capturing the input data: Data must be recorded or captured on some medium before they could be processed.
Manipulating the data: The following operations may be performed on the data.

(A) Classifying:
(B) Calculating:
(C) Storing:
(D) Summarising:

Handling the output results: Once data have been captured and manipulated, one or more of the following operations may be needed.

(A)Storing and Retrieving:
(B)Communicating and Reproducing:

Computer Processing Operations: A computer can perform only the following four basic operations through it can carry out the data processing activities.
(1) Input\Output operations
(2) Text manipulation and calculation operations
(3) Logic\Comparison operations
(4) Storage and Retrieval operations

Memory Capability

Computer systems have the ability of total and instant recall of data and an almost unlimited capacity to store these data. A typical mainframe computer system would have billions of characters and perhaps, thousands of graphic images, stored and available for instant recall.