Computer Network

 To build up a communication between two or more being is called network. Thus the processing of making communication between to more computer by cable, modem or satellite is called networking. In both decade by mini and mainframe computer first networking process was started on. Later on in the starting of 80th decade networking process started on through personal computer(PC). It is no need to say that in personal computer only one user can used it at the sane time. Due to networking in PC more than one user can use one computer at the same time. Again one user can use more than one computer at the same time. In short we can say that because of networking the entire computer computer under network automatically come under the same system. That means processing unit of all computers under same network being inter-connected is made into three categories   

Computer Network:

Operating System of Computers

Operating system: An operating system is a set of computer programs that enable the computer hardware to communication and operate with the computer software. Every computer must have an operating system to run other programs. The operating system (OS) is the first thing loaded onto the computer. Without an operating system, a computer and software programs would be useless. Operating system, a computer as controlling and allocating memory, prioritizing system requests, controlling input and output device, facilitating networking and managing file systems. The operating system is also responsible for security, ensuring that unauthorized users do not access the system. The name of some operating system is MS-DOS, Windows 3.0, Windows 95, Windows 98, Windows 2000 professional and Windows XP. Windows Vista, UNIX, Linux etc.

     

 Operating systems are classified into two categories:

  (a) Text based operating system.

  (b) Graphics user interface (GUI) operating system.

(a) Text based operating system:  

Operating systems, which are operated by text-based commands, is called text-based operating system. DOS and UNIX are text based operating system. OS/2 is a text based operating system but it can be used with the help of GUI operating system with GUI software.

(b) Graphics user interface (GUI) operating system:

Mac OS, Windows 3x, Windows 95, Windows 98, Windows 2000 professional, Windows XP, Windows NT, Windows Vista, LINUX are graphical user interface operating system. Most of the operational procedures are common in these operating systems. People also refer to it as a point and click interface because we use a mouse to point at on screen objects and then "click" them. Apple computer introduced the first successful GUI with its Macintosh computer in 1984.

Necessity of operating system:

Operating system has made the use of computer easier. GUI makes operating system very easier to the general people. As a result use of computer becomes easier. Operating system also makes the bridge between hardware and software for smooth and proper functioning of computer. No computer system can run without operating system. The internal task of computer are conducted or performed by the operating system. Operating system plays the role of manager for performed works of computers properly and effectively. So, operating system is the most and indispensable driving force of computer.

Block diagram of Computer:

For the task of computer its different parts are joined with each other connecting according to a special rule. A joined condition by the connection of different parts with each other is called system or organization or structure of a computer. Structure or organization of a computer generally means its hardware part. A block or schematic diagram of a digital computer is shown below.

                      (a)- Input device

                 (b)- Central processing Unit

                 (c)- Output device

     (a) Input device: If we want to do any task by a computer we must put data or instruction into it. By which device computer are given any instruction, data and program are called Input device or Instruction device a users can communicate with his computer. As input device Keyboard is used more. Beside there are different 

 Input devices.

• Mouse                             

• Scanner

• Modem                            

• Joy-stick

• Light pen                           

• Digital camera

• Hard Disk Drive                

• Floppy Disk Drive

• Compact Disk Drive         

• Digital Versatile Disk or Digital Video Disk Drive

• Punch Card                      

• OMR( Optical Mark Readers)

• Digitizer                            

• Graphics Tablet etc.

• OCR(Optical Character Recognition)           

     

(b) Central Processing Unit: Shortly central processing unit is called CPU. It is the main part of a computer. It is also called the 'brain' of the personal computer. All the functions of a computer is controlled by CPU. Basically the central processing unit consist of: control unit, arithmetic-logic unit and memory unit. These basic elements of the central processing unit are installed on a single semiconductor chip, which is called the microprocessor. In 1971 Intel company of America at first introduced microprocessor. Later on more improved microprocessor were available of which one chip contained whole CPU, RAM, ROM, 1/0 etc. So CPU of personal computer means microprocessor. It divided into three parts.

(a) Control Unit     (b) Arithmetic Logic Unit   (c) Memory Unit 

(a) Control Unit (CU): Control unit a controls whole functions of a computer. This unit receives an instruction from main memory, orders to arithmetic logic unit to solve different     arithmetic problems, transfers this results into output unit etc. In a word the control unit controls all the works.

(b) Arithmetic Logic Unit (ALU): Any arithmetic and logical problems are solved in the arithmetic logic unit of a computer. This unit solves arithmetic problem by addition, subtraction, multiplication or division and it examines logical sides of any problem. After processing result are stored into this unit.

(c) Memory Unit (MU): Function of memory unit is to store data program or result. This unit stores given instruction and data. It also stores periodical results. Memory can be divided into two parts.

        
     # Main memory or Primary memory.

     # Secondary memory or Auxiliary memory.

Output device: The result of given data or program into input unit is displayed in the output unit. After processing any problem we can get its result by this unit. The device are used for displaying result is called output devices. There are different kinds of output devices. As

        Monitor                Printer                  

        Speaker               Micro Film

        Plotter                  Disk Drive

        Tape Drive           Terminal   

        Microcosmic etc.

                                                            

History of Computer

          

                                 

                

We live in an age of science. We can see the wonders of science around us. Science has mad our life easy and comfortable we can't thing of our modern life with out science.

The first wonder of modern science is the discovery of Electricity.

It has changed our life, society, and culture .It is a great source of power and energy.

The radio, television, lights, fans, electronic iron, mills,factories and refrigerators all work though the power of electricity.

Science has invented many wonderful thing and computer is one of them. It is the most wonderful invention of modern science. 

Computer: 

The word computer is derived from the Latin word "computaer", which means a calculating machine. It was first used as a counting machine. Recently its uses and importance are seen dominating almost in the whole of our working fields. Computer is an ultra-modern electronic device. which accepts data through input device, stores and processes mathematically or logically and then sends the result through the output device according to the user requirements. It work on the given instruction of human being. 

 Computer Generation:

                                      Computer can not come to its present stage by one step. It has to go through many steps. In keeping with the improvement of electronics industries computer has also been improved. In 1951 first electronics computer UNIVAC ( Universal Automatic Computer ) was invent by heart and soul trying of some mathematicians. The age from 1951 even today can be divided into some generations. They are as follows.

(a) First Generation: From 1951 which computers are introduced as first generation computer. A main feature of first generation computer is to utilize tubes in their electronics circuits. Because of using huge numbers of vacuum tube a computer looked big in structure and needed more electricity.

 (b) Second Generation: from 1959 to 1965 which computers are introduced as the second generation computer. Main feature of second-generation computer were the using of transistors in the place of vacuum tubes. Because of using transistors second generation computers become in small structure and needed lower cost of electricity.

(c) Third Generation: From 1966 to 1970 which computers are introduced as third generation computers. Into those computers I.C. (Integrated circuit) were used.For using I.C. these computer become too small in structure and working efficiency was also upgraded. There are many Diodes, Transistors and other electronic parts in to an I.C. chip. More high level languages were used in third generation computers and its using also easy and simple.

(d) Fourth Generation: From 1971 to 1995 which computers are introduced are called fourth generation computers. This computers were produced with Large Scale Integration (LSI) and very large Scale Integration (VLSI) Microprocessors and semi conductor memory. As a result these computers were with high speed, high programming Language 'PASCAL' etc was the contributions of this generation.  

 (e) Fifth Generation: In 1981 at Japan 300 computer scientists and engineers of 14 countries declared as fifth generation computer, which would be produced after 1995. At that time scientists thought that fifth generation computers would be able to understand human language and according to those order or language they (computer) would be able to perform special task. This is why fifth generation computer would be enriched with artificial wit or brain.   

 

 
Type of Computers: On basis of structure, computer are classified in three type as-

                         

                              1- Digital Computer.

                              2- Analog Computer.

                              3- Hybrid Computer.

                    Digital Computer: A majority of the computers used in the world today are digital.A digital computer processes information which is based on the absence or presence of an electric plus, an on (1)/ off (0) condition. So a computer that counts the numbers and works directly on digits that represent either discrete data or symbols is called digital computer. These types of computers are able to give acute and error less result.  

                     Analog Computer: A computer that can measure continuous physical quantities such as electrical current, length, temperature, pressure, shaft rotations, voltage etc. and convert them to analogous decimal digits, and them realizes an arithmetic or logical operation and accomplished result is visible by meter or indicator is called analog computer, Speedometer of motorcar, thermometer etc. are ideal examples of analog machine. Analog computers are used mainly for scientific and engineering purposes because they deal with quantities that very constantly. These type of computers give approximate result only.    

                      Hybrid computer: The best combination of digital and analog computer is called hybrid computer. The hybrid computer takes analog inputs, converts them into digital data and processes them in digital form. Whether the output is digital or analog is a matter of requirement. These types of computers are used in real-time processing like whether forecasting and in the intensive care of a Hospital.

                           Classification of Computers:

    Computers are available in different size with different capabilities. They may be classified in the following four categories.

              1- Super Computer.

             2- Mainframe Computer, 

             3- Mini Computer.

             4- Micro or Personal Computer (PC). 

Super Computer: Super computer is the most powerful, expensive, and high speedy computer. In a few countries of recent world have super computer. It can perform more than crores of calculation within a second. This computer is being used sophisticated scientific research, cosmic research, and in the military affairs. Its sale and production are restricted.

Mainframe Computer: Mainframe computer is less powerful than the super computer than can analyses huge quickly. They are used in big research institutes, education institutes, banks, large organizations etc. A large number of users can use such a computer simultaneously.

 Mini Computer: A physically small and less working capability computer compared to mainframe is called mini computer. This type of computer can be set up in a large size table. Many users can use it simultaneously by connecting several terminals. Mini computer is generally used in Office, Banks, Clinics, Hospitals, Garments factory and multinational companies etc. The PDP Series of computers are mini computers.

Micro or Personal Computer(PC): In November, 1977 Intel company at first produced Microprocessor. This Microprocessor is introduced as Intel-4004, which is mainly used in calculator. The word Micro means very small. That is why a microcomputer made with mini microprocessor is called Microcomputer. Only one can use this type of computer at a time, so it is called Personal Computer (PC). A man in general stage could be able to use computer technology when the microcomputer came broad way. Besides in official works computer is being used extensively in home-works, sports, and recreations and in personal affairs. Microcomputer is mainly contained unique processor. Recently multiprocessor is being built with microcomputer. The working official processor used in Microcomputer is going to the way of development is so torrent that meanwhile the necessity of minicomputer is being mitigated by microcomputer. A few dates ago men could only think to used microcomputer setting on a desktop. At present it is also found in the shape of briefcase and mini books.