1. 1.         Definition of Computer

 

In a layman language, a computer is a fast calculating device that can perform arithmetic. Although the computer was originally invented mainly for doing high speed and accurate calculations, it is not just a calculating device. It gets the data through an input device, processes it as per the instructions given and information as output. We can define a computer follows.

 

“A computer is fast electronic device that processes the input data according to the instructions given by the programmer/user and provides the desired information as output”.

 

Term	Meaning
Data	A set of basic facts and entities which itself has no Meaning.
Information	Data which has some meaning or value.
Instruction	A statement given to computer to perform a task
Input	Data and Instructions given to computer
Process	Manipulation of data
output	Information obtained after processing of data

 

1. 2.         Importance of Computer

 

Computer plays a vital role for processing of data in an organization. Computers help in processing volumes of data efficiently and accurately within short time.

 

A computer has the following characteristics, which makes it so important for an organization:

 

1. Fast: A computer is so fast that it can perform the given task (arithmetical of logical) in few seconds as compared to man who can spend many months for doing the same task. A computer can process millions of instruction per second.

 

1. Accurate: While doing calculations, a computer is more accurate than a man. Man can make mistakes in calculations but a computer does not, if it is provided with accurate instruction.

 

1. High Memory: A computer has much more memory of storage capacity than human beings. It can store millions of data and instructions, which can be retrieved and recalled even after number of years. This in not possible in cast of human brain.

 

1. Diligence: A computer does not surer from the human traits of tiredness and boredom. Man will be tired and bored while doing millions of calculations but computer, being a machine, does this jobs very efficiently and without any tiredness and boredom.

 

1. No Intelligence: A computer is a machine and obviously has no intelligence of its own. Each and every instruction must be given to the computer for doing a task. Man has intelligence and it is the man who invented computer and gives it all the instructions and logic to work. The main drawback of computer is that it cannot take decisions on its own.

 

 

1. 3.         Classification of Computer

 

The classification of computers is based on the following four criteria:

 

1. According to purpose

 

1. According to Technology Used

 

1. According to Size and Storage Capacity

 

1. According to Historical Advancement

 

            According To Purpose

 

According to the utilization of computer for different uses, computers are of the following two types;

 

1. 1.     general Purpose Computers

 

Computers that follow instructions for general requirements such as sale analysis, financial accounting, inventory and Management information etc. are called general computers. Almost all computers used in offices for commercial, educational and the applications are general-purpose computers.

 

1. 2.     Special Purpose Computers

 

Computers that are designed from scratch to perform special tasks like scientific applications and research, whether forecasting space applications, medical diagnostics, etc. are called special purpose computers.

 

            According To Technology Used

 

According to the technology used, computers are of the following three types;

 

1. 1.     Analog Computer

 

Analog computers are special purpose computer that represent and store data in continuously varying physical quantities such as current, voltage or frequency these computers are programmed for measuring physical quantities like pressure, temperature, speed etc. and to perform computations on these measurements. Analog computers are mainly used for scientific and engineering applications. Some of the examples of analog computers are given below:

 

(i)                            Thermometer: It is a simple analog computer used to measure temperature. In thermometer, the mercury moves up or down as the temperature varies.

 

(ii)                         Speedometer: Car’s speedometer is another example of analog computer where the position of the needle on dial represents the speed of the car.

 

2. Digital Computer

 

Digital computers are mainly general-purpose computers that represent and store data in discrete             quantities or numbers. In these computers, all processing is done in terms of numeric representation (Binary Digits) of data and information. Although the user enters data in decimal or character form, it is converted into binary digits (0’s and 1’s). Almost all the computers used nowadays are digital computers.

 

3. Hybrid Computers

 

Hybrid computers in corporate the technology of both analog and digital computers. These computers store and process analog signals, which have been converted, into discrete numbers using analog-to-digital converters. They can also convert the digital numbers into analog signals or physical properties using digital-to- analog converters. Hybrid computers are mainly used in artificial intelligence (robotics0 and computer aided manufacturing (e.g. process control).

 

            According To Size and Storage Capacity

 

According to the size and memory/storage capacity, computers are of the following four types:

 

1. Micro Computer: Micro Computers are the smallest category of computer consisting of a microprocessor and associated storage and input-output elements. They are designed to be used by one person at a time, meaning they are single user oriented ones.

 

1. Mini Computers: Mini computers are relatively fast but small and expensive Computers with some what limited input/output capabilities. Mini systems are designed to simultaneously handle the processing needs of multiple user. Mini Computer provides the facility of more stored capacity and communication link between users.

 

1. Mainframe Computers: Mainframe computers are large computer systems that have the capability to support many powerful peripheral devices.

 

1. Super Computer: Computers system characterized by their very large size and very high processing speed. Generally used for complex scientific applications.

 

 

4. Input/Output Unit

 

We know that the computer is machine that processes the input data according to given set of instructions and gives the output. Before a computer does processing, it must be given data and instructions.

 

After processing, the output must be displayed or printed by the computer. The unit used for getting the data and instructions into the computer and displaying or printing output is known as an Input/Output (I/O unit). The Input Unit is used to enter data and instructions into a computer. There are many peripheral devices which are used as Input/Output unit for the computer. The most common form of input device is known as a terminal. A terminal has an electronic typewriter like device, called keyboard along with a display screen, called Visual Display Unit (VDU) or monitor. Keyboard is the main input device while the monitor cab be considered both as input as well as an output device. There are some other common input devices like mouse, punched card, tape, joystick, scanner, modem etc., Monitor, Printer and Plotter are the main peripheral devices used as output units for the computer.

5. Center Processing Unit (CPU)

Fig. 1.1- Functional diagram of a generalized architecture of a computer system CPU is the main component or “brain” of computer, which perform all the Processing of input data. Its function is to fetch, examine and then execute the instructions stored in the main memory of a computer. In microcomputers. The CPU is built on a single chip or Integrated Circuit (1C) and is called as a Microprocessor. The CPU consists of the following distinct parts:

 

1. Arithmetic Logic Unit (ALU)

 

1. Control Unit (CU)

 

1. Register

 

1. Buses

 

1. Clock

 

            Arithmetic Logic Unit (ALU)

 

The arithmetic logic unit of CPU is responsible for all arithmetic operations like addition subtraction, multiplication and division as well as logical operations such as less than, equal to and grater than. Actually, all calculations and comparisons are performed in the arithmetic logic unit.

 

            Control Unit (CU)

 

The Control unit is responsible for controlling the transfer of data and instructions among other units of a computer. It is considered as the “Central Nervous System” of computer, as it manages and coordinates all the units of the computer. It obtains the instructions from the memory, interprets them and directs the operation of the computer. It also performs the physical data transfer between memory and the peripheral device.

 

            Registers

 

Registers are small high speed circuits (memory locations) which are used to store data, instructions and memory addresses (memory location numbers), when ALU performs arithmetic and logical operations. Registers can store one word of data (1 word =2 bytes & 1byte = 8 bits) unit it is overwritten by another word. Depending on the processor’s capability, the number and type of registers very from one CPU to another. Registers can be divided into six categories viz. General Purpose Registers, Pointer Registers, Segment Registers, Index Registers, and Flag Register and Instruction Pointer Register, depending upon their functions.

 

            Buses

 

Data is stored as a unit of eight bits (BIT stands for Binary Digit i.e. 0 or 1) in a register. Each bit is transferred form one register to another by means of a separate wire. This group of eight wires, which is used as a common way to transfer data between registers, is known as a bus. In general terms, bus is a connection between two components to transmit signal between them. Bus can be of three major types viz. Data Bus, Control Bus and Address Bus. The data bus is used to move data, address bus to move address or memory location and control bus to send control signals between various components of computer.

 

            Clock

 

Clock is another important component of CPU, which measures and allocations a fixed time slot for processing each and every micro-operation (smallest functional operation). In simple terms, CPU is allocated one or more clock cycles to complete a micro-operation. CPU executes the instructions in synchronization with the clock pulse. The clock-speed of CPU is measured in terms of Mega Hertz (MHz) or Millions of Cycles per second. The clock speed of CPU varies from one model to another in the range. 4.77 MHz (in 8088 processor) to 2266 MHz (in Pentium II). CPU speed is also specified in terms of Millions of Instructions Per Second (MIPS) or Million of Float-ing-Point Operations Per Second (MFLOPS).

 

6. History of Computers

 

Computer history starts with the development of a device called the abacus by the Chinese around 3000 BC. This was used for the systematic calculation of arithmetic operations. Although here were a number of improvements in calculating devices, no conceptual changes were made until the end of the 8th century. During the first decade or the 19th century, Jacquard invented an automated loom operated by a mechanism controlled by punched cards. During the same period charles Babbage developed his differential and analytical engines. This device had provisions for inputting data, storing information, performing arithmetic operations and printing out results. This provided a base for the modern computer.

Fig 1.2 devices used in different generations of computer

 

At the end of the nineteenth century, Herman Hollerith and James Powers designed a data processing machine for processing census information. Hollerith developed codes for processing both alphabetical and numerical data. A significant machine built in the early 1940s was Mark which utilized electromagnetic relays. Later in the 1940s the first electronic machine known as ENIAC (Electronic Numerical Integrator and Calculator) was introduced.

 

During the period, 1946-52, John Von Neumann and his team developed a high-speed digital computer using vacuum tubes. This machine mainly served as a laboratory to test many or the notions of programming and coding used in modern computers.

 

7. Computer Generations

 

Unit 1950 the major contributions were from the Universities and Research Institutions. Almost all the later developments were due to the computer manufacturers.

 

From the early 1950s, computers started appearing in quick succession, each claiming an improvement over the other. They represented improvements in speed, memory (storage) systems, input and output devices and programming techniques. They also showed a continuous reduction in physical size and cost. The developments in material technology, particularly the semiconductor technology.

 

Computers developed after ENIAC have been classified into the following five generations:

 

First generation 1946-1955

Second generation 1956-1965

Third generational 1966-1975

Fourth generation 1999-1975

Fifth generation 1996-present

 

You may notice that, from 1946, each decade has contributed one generation of computers. The first generation computers are those in which vacuum tubes are used. Magnetic drives and magnetic core memories were developed during this period.

 

All the first generation computer possessed the following characteristics as compared to the later models:

 

1. Large in size.
2. Slow operating speeds.
3. Restricted computing capabilities.
4. short life span
5. Complex maintenance schedules

 

The Second Generation computers were marked by the use of solid-state device called the transistor in the place of vacuum tubes. All these machines 19. were much faster and more reliable than their earlier counterparts. Further, they occupied less space, required less power and produced much less heat.

 

The research in the field of electronics led to the innovation of the integrated circuits, now popularly known as IC chips. The use of IC chips in the place of transistors gave birth to the third generation computers. They were still more compact, faster and less expensive, than the previous generation.

 

Continued efforts towards miniaturizations led to the development of large scale integration (LSI) technology. Intel Corporation introduced LSI chips called microprocessors for building computers. The latest child of the computer family that uses LSI chips has been names the fourth generation computer. The fourth generation computers are marked with an increased user-computer inter-action and speed.

 

Japan and many other countries are working on systems who are known as expert systems which will considerably improve the man-machine interaction. Such systems would integrate the advancements in both hardware and software technologies and would facilitate computer-aided problem-solving with the help of organized information in many specialized areas.

 

The generation of computers is termed as fifth generation computers. Although expert systems are expansive and time-consuming to build, they are likely to become more popular in the next few years.