Chapter 1 Introduction to Computer

Chapter 1 Introduction to Computer 1.1 What is a computer? We will briefly present as three points of view. From a functional point of view, a computer is an information processing system (IPS) capable of storing and manipulating numbers, words (symbols), and pictures. From an organizational point of view, a computer system consists of hardware (equipment) and software (programs) and sounds. From a users point of view, a computer may be a teaching machine, a source of reference materials such as dictionaries and encyclopaedias, a companion for playing games and tool for problem solving. To summarize the three points of view, we can define a computer is a collection of hardware and software for (a) data processing (e.g. calculation) (b) information processing (e.g. database) and (c) knowledge processing (e.g. A.I) The hardware is physical part of the system, such as the system unit, video monitor, printer, keyboard, mouse, scanner and other peripheral devices. Software is the name given to any kind of program which tells the hardware what to do. The hardware is visible and tangible and the software is the soul of the machine. A computer without software is like a car without gasoline, a camera without film, a stereo without records. A Computer is neither intelligent nor stupid. It slavishly follows the instructions given by the human user known as the programmer. 1.2 History of Computing In the early days man used to count with his fingers and manipulate numbers manually. But technological developments demanded faster computing devices. This led to the development of computers. The Abacus and Personal Computer are two such devices separated by thousands of years of history. 1. Early Calculating Devices - Abacus - Napier's Bones 5000 BC - Oughtrad's Slide Rule to - Pascal's Calculator 1936 AD - Jacquard's Loom - Babbage's Difference Engine - Babbage's Analytical Engine - Herman Hollerith-Punched Cards 2. Middle Age Computer - Mark I Computer 1937 - ABC to - ENIAC 1946 - Stored Program Concept - EDVAC 3. Modern Age Computer - 1st Generation Computer 1948 - 2nd Generation Computer to - 3rd Generation Computer Date - 4th Generation Computer - 5th Generation Computer 1.2.1 Early Calculating Devices Abacus (5000 BC) The Abacus was used in 5000 BC for counting and computations. It consists of a frame with some bars fixed across it. Each bar had some beads which could be moved along each bar.Every bead represented a position in the number system. Napier’s Bones John Napier, a Scottish Mathematician invented a tool which helped him in doing the tedious calculations involved in Astronomy. For this he used 10 strips of bones called Napier’s Bones and divided each into 9 squares. Again each square was divided into 2 parts. The lower half indicated units and the upper half indicated tens. Oughtrad's Slide Rule Napier also developed the method of logarithm. In the algorithm method, multiplication and division can be done by adding and subtracting not the numbers themselves, but with the help of related numbers, known as logarithms. All engineering calculations are being done with the help of logarithms. In 1620, William Oughtrad invented the slide-rule which is a calculation device that uses the principle of logarithms. Pascal’s Calculator (1642) In 1642, the great French mathematician and philosopher Blaise Pascal devised a calculating machine. The machine consisted of gears, wheels and dials. Each wheel had 10 segments like that of house energy meters. When one wheel completed a rotation, the next wheel moved by one segment. With this calculator, addition and substraction could be performed by dialing these series of wheels bearing the numbers 0 to 9 around their circumference. Jacquard’s Loom (1801) A French weaver, Joseph Jacquard used punched cards (Jacquard’s Loom) to determine the threads to be selected in weaving patterns automatically. A hole in the card permitted a hooked wire containing a thread to enter the pattern which the absence of a hole would correspondingly prevent. Babbage’s Difference Engine and the Analytical Engine Charles Babbage, a genius in the history of computing made a machine called Differential engine which could evaluate accurately algebraic expressions and mathematical tables correct upto 20 decimal places. Later on Babbage developed Analytical Machine. It was supposed to be a general purpose computer that could add, subtract, multiply, and divide in automatic sequence at a rate of 60 additions per second. His design would cover the area of a football field and be powered by a locomotive engine. He could not complete his work. In 1991 London’s Science Museum spent $600,000 to build a working model of the difference engine, using Babbage’s original plans. The result stands 6 ft high, 10 ft long, contains 4000 parts, and weighs 3 tons. He used punched cards to enter data. His idea had all the basic components of today's modern computer. Therefore, he is called the Father of Modern Computers. Herman Hollerith’s Tabulating Machine(1890) Dr Herman Hollerith of the United States of America was the next contributor to development of computer. He invented a machine which used punched cards to store and tabulate census information.This machine could sense the punched holes, recognize the number, and make the required calculations. 1.2.2 Middle Age Computers IBM Mark I In 1937, Harvard professor Howard Aiken set out to build an automatic calculating machine to combine electrical and mechanical technology with Hollerith's punched card techniques. In 1944 the mark I Digital computer was completed. Internal operations were controlled automatically with electromagnetic relays, arithmetic counters were mechanical computer. This was 15m long and weighed nearly 1500 tons. ABC (Atanassoff - Berry - Computer) During 1937-1938, Dr. John Vincent Atanassoff, a professor of physics and mathematics at Iowa State College, teamed up with Clifford Berry, his graduate assistant and began to build the first electronic computer. They call it the ABC. The ABC used vacuum tubes for storage and arithmetic logic functions. This was designed for the special purpose of simultaneous equations. ENIAC (Electronic Numerical Integrator And Calculator) In 1940 and 1941, Mauchly teamed up with J. Presparo Eckert, Jr, to construct ENIAC. ENIAC was the first electronic general-purpose computer to be put into full operation; vacuum tubes were used in ENIAC. It weighed 30 tons and could do 300 multiplications per second. Stored Program Concept In the mid 1940, H.Goldshine, A.W Burks and John Von Newmann wrote a paper suggesting: 1. Binary numbering systems can be used in building computers. 2. Computer instructions as well as the data being manipulated could be stored internally in the machine. The first of these was an important idea because the numbering system is represented by only two digits (0 and 1) and also electronic components are typically in one of the two conditions 'on' or 'off'. So, the binary concept made equipment design simpler. The second idea called the stored program concept, was a brilliant breakthrough because it meant that programs could simply be entered into memory like data. EDVAC Mauchly, Eckert and others at the Moore school set out to build a machine with stored program capability. This machine was called EDVAC. It carries the distinction of being the first stored program electronic computer. 1.2.3 Modern Age Computers First Generation Computers The first generation (1940) of component including vacuum tubes. The vacuum tubes were fragile, subject to overheating and caused frequent breakdowns. Machine language were used during this period. e.g. ENIAC Second Generation Computers The second generation of computers (1959) used transistors instead of tubes. Transistors were smaller, faster and more reliable and produced far less heat during operation, much smaller device based on semiconductor. e.g. IBM 1401, LEO III, UNIVAC and ANLAS Third Generation Computers The development of integrated circuit (IC) technology in the mid-1960. DRAM were used for primary storage. e.g. ICL 1900 series, IBM 360 series Fourth Generation Computers This generations typified by large scale integration (LSI) of circuits which allowed the development of the microprocessor, which in turn allowed the production of the microcomputer(1974). It is a more powerful, reliable and compact computer. All computers used today make use of such silicon chip technology. e.g. Silo Z80, Inter 8086, 8088, 80286, .... Fifth Generation Computers Fifth generation computing devices, based on artificial intelligence, are still in development, through there are some applications, such as voice, recognition, that are being used today. The use of parallel processing and superconductors is helping to make artificial intelligence a reality. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization. 1.3 Classification of Computers Computer systems are classified by their CPU sizes, number of on line terminals, maximum disk storage capacity, and all other available I/O devices into the following categories: 1. Microcomputers 2. Minicomputers 3. Mainframes 4. Supercomputers. 1.3.1 Microcomputers Microcomputers are also called personal computers. Each contains a microprocessor and is designed for individual personal use. Classifications within this category include non-portable and portable computers. The mosty popular type of microcomputer, desktop computers, are designed to fit on top of desk. Portable computers include laptop, notebook, sub notebook and pen based. Laptop computers are the largest portable computers in this category. Notebook computers are smaller versions of the laptop computers. Sub notebook computers are even smaller than notebook computers. Pen based computers are the smallest computers and use a pen-like device to enter data. This pen-like device can be used to write directly on the screen or can be used as a pointer to make selections from a menu displayed on the screen. 1.3.2 Minicomputers Minicomputers are referred to as task-oriented computers. They are more powerful than microcomputers in terms of multiple user environments. In other words, many operators can use a minicomputer simultaneously. The most powerful minicomputers are called super minicomputers. 1.3.3 Mainframe Computers Mainframe computers are large computer systems that can handle hundreds of users, store large amount of data, and process transactions at a high speed. 1.3.4 Super Computers Super computers are to the largest, most expensive real-time computer systems. Super computer generally have CPUs of 5000k or more, online disk storage which store billions of characters. They are large, complex systems and use high-speed telecommunication facilities, such as satellites. Super computers react instantly to a variety of conditions and can normally execute millions of instructions each second. Their ability to carry out 50 to 100 million instructions per second sets them apart from most systems. 1.4 Structure of a Digital Computer A digital computer may be divided into the following fundamental units: a) Input Devices The input devices read the necessary data into the machine. A computer cannot deal with data unless in a language it understands. The input unit is provided to translate all data into electronic pulses so that computers can understand it. In most general-purpose computers, the instructions that constitute the program must be fed into the machine along with all the data to be used in the computations.Some of the more common input devices are keyboards, punched-card, magnetic tape readers etc. CPU INPUT ALU CU OUTPUT DEVICE DEVICE IMMIEDIATE ACCESS STORE BACKING STORAGE Block Diagram of a Digital Computer b) Central Processing Unit The CPU is the main part of a computer in which all processing is carried out. It also controls the activities of the whole computer configuration. It comprises there components namely: 1. Arithmetic and Logic Unit 2. Control Unit 3. Memory The functions of a CPU are to: 1. Store data as well as instructions. 2. Control the sequence of operations as per the stored instructions. 3. Issue commands to all parts of computer system. 4. Carry out data processing and to send results to output. 1. Arithmetic and Logic Unit (ALU) The ALU operates on the data available in the main memory and send them back after processing, once again to memory. The functions of the ALU are 1. It carries out arithmetic operations like additions, subtraction, multiplication and division. 2. It performs certain logical actions based on AND and OR functions. 2. Control Unit The control unit directs all operations inside the computer. It is known as the heart of the computer because it controls and coordinates all hardware operations i.e. hose of the CPU and input output devices. The main functions of the control unit are: 1. It gives commands to transfer data from the input device to the memory to the Arithmetic logic unit. 2. It also transfers the results from memory to the output device for printing. 3. It stores the program in the memory, takes instructions one by one, understands them and issues appropriate commands to the other units. 3. Memory It is also called the computer's main memory or primary memory because it is able to store information, which can be recalled or accessed when required. The program insturctions has to be stored in the main memory in order to make it work automatically. The memory is make of electronic components due to which its operation is extremely fast. Main high speed memory is limited in size and very costly to buy; as such, only limited memory is provided. The rest of the programs and data are kept in secondary storage devices also known as backing storage devices. The main functions of the memory are to store: 1. Instructions waiting to be obeyed by other components of the CPU. 2. Instructions currently being obeyed. 3. Data awaiting processing. 4. Data currently being processed. 5. Processed data awaiting output. c) Output Devices The results of any computer processing have to be communicated to the user. Output devices translate the computer output into a form understood by human beings. Common output devices are CRT displays, printers, card-readers etc. The five basic units of a computer can be summarised as in the following table. Unit Function Input Reads information from input device and feeds to the computer in coded form. Storage Unit Stores program instructions and data. Arithmetic & Logic Unit Performs arithmetic and logic operations. Control Unit Interprets program instructions and initiates control operations. Output Unit Decodes information and presents it to the user. 1.5 Software A software program is actually a set of instructions written in various computer languages by programmers. There are two main types of software. They are (1) System software (2) Application software. 1.5.1 System Software System software consists of programs that are used to control and operate the computer hardware. There are three components in system software: the operating system, utility programs and language processors. The operating system tells the computer how to perform functions such as how to load, store and execute programs, how to manage resources available (CPU time). Utility program are designed to perform functions that are not available in application software, such as formatting a diskette and creating a directory. 1.5.2 Application Software Application software consists of programs created to perform a specific user's task. Application software allows a user to prepare a document, design a financial worksheet or create a useful database. Main frame The main frame is the workhorse of the business world. A main frame is the heart of a network of computers or terminals which allows hundreds of people to work at the same time on the same data. It requires a special environment - cold and dry. Personal or micro Computers for personal use come in all shapes and sizes, from tiny PDAs (personal digital assistant) to hefty PC (personal computer) towers. More specialized models are announced each week - trip planners, expense account pads, language translators... Hand-held (HPC) PDA Tablet PC Laptop/Notebook Desktop Tower   Workstation When talking about PC computers, most people probably think of the desktop type, which are designed to sit on your desk. (Bet you figured that one out!) The tower and the smaller mini-tower style cases have become popular as people started needing more room for extra drives inside. Repairmen certainly appreciate the roominess inside for all the cables and circuit boards ... and their knuckles. A workstation is part of a computer network and generally would be expected to have more than a regular desktop PC of most everything, like memory, storage space, and speed. The market for the smallest PCs is expanding rapidly. Software is becoming available for the small types of PC like the palmtop (PPC) and handheld (HPC). This new software is based on new operating systems like Windows CE (for Consumer Electronics). You may find simplified versions of the major applications you use. One big advantage for the newer programs is the ability to link the small computers to your home or work computer and coordinate the data. So you can carry a tiny computer like a PalmPilot around to enter new phone numbers and appointments and those great ideas you just had. Then later you can move this information to your main computer. With a Tablet PC you use an electronic stylus to write on the screen, just like with a pen and paper, only your words are in digital ink. The Tablet PC saves your work just like you wrote it (as a picture), or you can let the Hand Recognition (HR) software turn your chicken-scratches into regular text. Supercomputers The supercomputer is the top of the heap in power and expense. These are used for jobs that take massive amounts of calculating, like weather forecasting, engineering design and testing, serious decryption, economic forecasting, etc. The first Cray supercomputer was introduced in 1976 9 Computer Systems and Computer Programming Computer Systems and Computer Programming 8