Note for Computer Programming - CP by Jyotirmayee Reddy

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MODULE 1 INTRODUCTION TO COMPUTERS The term computer is derived from the word compute. A computer is an electronic device that takes data and instructions as an input from the user, processes data, and provides useful information known as output. This cycle of operation of a computer is known as the Input-Process-Output cycle shown in figure. The electronic device is known as hardware and the set of instructions is known as software. INPUTOUTPUT Data PROCESS Information Instructions Fig: Input –Process-Output Concept COMPUTER SYSTEM CHARACTERISTICS Computer is 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. 1) Speed:Computer executes one instruction at a time. Most instructions are carried out in less than a millionth of a second. 2) Accuracy: Since the circuits in a computer have electronic parts, which far do not have wear and tear, the instructions are carried out without any mistakes. 3) Vast Storage Media: In a computerized system a very large amount of data can be stored. Modern computers possess certain characteristics and abilities     Perform complex and repetitive calculations rapidly and accurately Store large amount of data and information for subsequent manipulations Compare items and make decisions Provide information to the user in many different forms 1

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   Automatically correct or modify the parameters of a system under control Draw and print graphs Receive and display audio and video GENERATIONS OF COMPUTERS The different computing devices developed over the years can be categorized into several generations. Each generation of computer is the result of a technological development, which changed the way computers used to operate. Computers can be categorized into five generations:      First generation(1940-1956) Second generation(1956-1963 ) Third generation(1964-1971) Fourth generation(1971-Till Date ) Fifth generation(1980s…) First –Generation Computers In this generation of computers, vacuum tubeswere used to build the circuitry for the computers and magnetic drum was used for the memory of the computer. A vacuum tube was a device made up of glass and used filaments to generate electrons. It was used to amplify the electronic signals. These computers used to perform calculation in milliseconds. The size of these computers was very large, and a single computer was used to cover the space of an entire room. Since the size of the computers was very large, they used to consume a great deal of electricity and generated a large amount of heat. To avoid malfunctioning from overheating, the rooms where these computers were placed had to be air-conditioned. They used machine language to perform operations and were capable of performing one operation at a time. The first generation computers are ENIAC, EDVAC and UNIVAC. These computers were used for scientific calculations. Second-Generation Computers In the second generation of computers, transistors were used instead of vacuum tubes. They are faster and more reliable than vacuum tubes. In addition the size of transistors was smaller than vacuum tubes and they generate less heat as compared to vacuum tubes. 2

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They used assembly language instead of machine language .The use of assembly language helped the programmer to specify instructions in the form of words. The main characteristic of second generation computers was that they used the stored program concept, i.e. the instructions were stored in the memory of the computer. These computers usemagnetic tapes and magnetic disks as external storage devices.IBM 1620, PDP8 and CDC1604 are examples of second generation computers. Third-Generation Computers They were characterized by the development of the integrated circuit (IC). An IC is a silicon chip that embeds an electronic circuit, which comprises several components, such as transistors. The use of ICs had increased the speed and efficiency of the computers to a significant extent. Third generation computers include IBM 370, PDP11 and CDC7600 etc. Fourth-Generation Computers Fourth generation computers use Large Scale Integration (LSI) circuits and Very Large Scale Integration (VLSI) circuits in the construction of computing components. LSI and VLSI circuits were further integrated on a single silicon chip, termed as microprocessor, containing control logic and memory. The Intel 4004 chip was the first microprocessor for the computers of this generation. The major change in the fourth generation of computers was seen in the replacement of magnetic core memories by semiconductor memories. For enabling connection and communication among multiple computers at one time they use two types of high speed computer networking. The first one is the Local Area Network (LAN), where multiple computers in a local area are connected and allowed to communicate among them. The second type of networking is the Wide Area Network (WAN), which facilitates connection and communication of hundreds of computers located across multiple locations.Fourth generation of computers used high-level programming languages. They have large primary and secondary storage memory. Examples are IBM 4300 and ICL 2900. Fifth-Generation Computers Fifth generation of computers is characterized by the Ultra Large ScaleIntegration technology, which is more powerful as well as faster than the microprocessors used by the computers of the fourth generation.The PCs in the fifth generation have become portable, which are much smaller than the fourth generation PCs. There are some computing 3

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devices of the fifth generation still in the development phase, which are based on artificial intelligence. BLOCK DIAGRAM OF COMPUTER A Computer has four main components 1) 2) 3) 4) Central Processing Unit( CPU ) Memory Input device Output Device Input Device Output Device memory N I . S E NOT ALU KTU CU CPU Fig:-Block Diagram Of Computer Central Processing Unit( CPU ) The CPU acts as the computer brain.CPU is responsible for the overall working of all components of the computer. It consists of two parts: Arithmetic and Logic Unit (ALU) and Control Unit (CU) .The ALU performs arithmetic operations and conducts the comparison of information for logical decisions. The control unit is responsible for sending / receiving the control signals from / to all components. The dotted lines in the above diagram represent the communication of control signal, whereas the solid lines denote the transfer of data. Under the control of CU, the data comes from input device(s) to memory, it is processed in ALU and the result is stored back in the memory. The processed results are displayed with the help of an output device. 4