1. UNIT 1 2. What is Computer ?? The word computer comes from the word compute which means to calculate A computer is an electronic device that can perform arithmetic operations at a high speed A computer is an electronic device that manipulates information, or data. It has the ability to store, retrieve, and process data. 3. Functionalities of a Computer Any digital computer carries out five functions : Takes data as input. Stores the data/instructions in its memory and can use them when required. Processes the data and converts it into useful information. Outputs the information. Controls all the above four steps. 4. Characteristics of a Computer Speed: The computer is a very high speed electronic device. The operations on the data inside the computer are performed through electronic circuits according to the given instructions. Arithmetical and Logical Operations: A computer can perform arithmetical and logical operations. Accuracy: In addition to being very fast, computer is also very accurate device. It gives accurate output result provided that the correct input data and set of instructions are given 5. Characteristics of a Computer Reliability: The electronic components in modern computer have very low failure rate. Storage: A computer has internal storage (memory) as well as external or secondary storage. Automation: A computer can automatically perform operations without interfering the user. Versatility: Versatile means flexible. Modern computer can perform different kind of tasks one by one of simultaneously. 6. Characteristics of a Computer Communications: Today computer is mostly used to exchange messages or data through computer networks all over the world. Diligence: A computer can continually work for hours without creating any error. Feelings: Computer is an electronic machine. It has no feelings. Consistency: People often have difficulty to repeat their instructions again and again. . Computer can repeat actions consistently 7. Advantages of Computer Computational and clerical work easy. Buying and banking more. Easy access to lot of useful information. Communicate and keep in touch with others. Entertainment with technologies It can store large amount of facts, instructions, and information. It can process data with accuracy at a very high speed. 8. Disadvantages No Feelings and IQ Specialized Tasks Hardware Limitation Data Tampering costly as compared to the pen and pencil they replaced. Using computer requires additional efforts in form of developing software and learning to use computers. Once an application on computer is developed and implemented, it becomes difficult to make even minor modification. A computer can only perform operations programmed or instructed by a person. It cannot correct wrong instructions by itself. 9. Applications of Computer Education Science Medicine and Healthcare Engineering/Architecture Communication Publication Entertainment Banks Reservations 10. Evolution of Computers ABACUS- It is a counting device which has emerged about 5,000 years ago in Asia Minor and is still in use today, may be considered the first computer. This device allows users to make computations using a system of sliding beads arranged on a rack. Pascaline Machine - In 1642, Blaise Pascal (1623-1662), invented first functional automatic calculator called Pascaline Machine. This brass rectangular box, also called a Pascaline, used eight movable dials to add sums up to eight figures long. The drawback to the Pascaline, of course, was its limitation to addition. 11. Evolution of Computers Leibniz Machine- In 1694, a German mathematician and philosopher, Gottfried Wilhem von Leibniz (1646-1716), improved the Pascaline by creating a machine that could also multiply, divide and find the square root. Leibniz's mechanical multiplier worked by a system of gears and dials. It lacked mechanical precision in its construction and was not very reliable. Charles Babbage- Charles Babbage, a 19th century professor is considered as father of modern digital computers. In 1842, he came up with his new idea of analytical engine, which was completely automatic. It was capable of performing basic arithmetic functions for any mathematical problem. But he was not able to produce it working model. He proposed another machine to perform differential equations called difference engine powered by steam and large as locomotive, the machine would have stored program and could perform calculations and print result automatically. 12. Evolution of Computers 13. Evolution of Computers In 1889, an American inventor, Herman Hollerith (1860-1929), also applied the Jacquard loom concept to computing. His first task was to find a faster way to compute the U.S. census. He gave the concept of punched cards. Punched cards were used as input medium in computers. Holleriths method used cards to store data information which he fed into a machine that compiled the result mechanically. 14. Some Early Computers THE MARK I COMPUTER: [1937-44] Invented by Howard. A. Aiken. Known as Automatic sequence Controlled Calculator. Though this machine was reliable, it was very complex in design and huge in size. It is used over 3000 electrically actuated switches to control its operation and was 50 feet long and 8 feet high. It was capable of doing 5 arithmetic operations: addition, subtraction, multiplication, division and table reference on numbers. 15. Some Early Computers THE ANANASOFF - BERRY COMPUTER:[1939-42] Invented by Dr. John Atanasoff. Electronic machine to solve certain mathematical equations. It used 45 Vacuum tubes for internal logic and capacitors for storage. THE ENIAC:[1943-46] Invented by John Mauchly. Abbreviation for Electronic Numerical Integrator and Calculator. Developed for military needs. Uses 18000 vacuum tubes. It could add 2 nos in 200 ms and multiply in 2000ms. 16. Some Early Computers THE EDVAC:[1946-52] Invented by Dr. John Von Neumann. Abbreviation for Electronic Discrete Variable Automatic Computer. A sequence of instructions and data can be stored in the memory of a computer for automatically directing the flow of operations. Due to this, we often refer to modern digital computers as stored programs digital computers. THE EDSAC:[1947-49] Abbreviation for Electronic Delay Storage Automatic Calculator. In this machine, addition operations took 1500ms and multiplication operations took 4000ms. 17. Some Early Computers THE UNIVAC:[1951] Abbreviation for Universal Automatic computer. The first UNIVAC machine was installed in census bureau in 1951. In rapid succession, improved models of univac-1and other 700 series were introduced. UNIVAC marked the arrival of commercially available digital computers for business and scientific applications. 18. Computer Generations By Generation, we mean a step ahead in technology. There are five generations: (I)First Generation Computers (1940 to 1956): 19. Computer Generations First Generation Computers (1940 to 1956): Characterized by vacuum tubes in the circuitry and magnetic drums for memory. A magnetic drum is a metal cylinder coated with magnetic iron-oxide material on which data can be stored. Enormous in size, used great electricity and were expensive to operate, limited storage Uses machine language (binary) to perform operations. Could solve only one problem at a time. ENIAC, EDVAC and UNIVAC can all be classified as first generation computers. Advantages: These computers were based on vacuum tube technology. Fastest computing devices of their times. Disadvantages: Too bulky in size. Generate large amount of heat because of use of thousand of vacuum tubes. Non-portable and very slow equipments. Lacked in versatility and speed. Expensive to operate and used a large amount of electricity. Unreliable and Prone to frequent hardware failure. So, constant maintenance was required. Difficult to program and use since machine language was used. Limited commercial use because each individual component had to be assembled manually. 20. Computer Generations Second Generation Computers (1956 to 1963) : In the early 1950s, the discoveries of Transistor and Magnetic core memory changed the image of computers from unreliable to highly reliable machines with increased capability, and higher storage capacity. The transistor was far superior to the vacuum tube, allowing computers to become smaller in size, cheaper, reliable and more energy efficient. Though transistor still generated a great deal of heat, it was a substantial improvement. characterized by allowing programmers to specify instructions in symbolic language. Example:-PDP-8, IBM 1401. Advantages: Smaller in size compared to first generation computer because of Transistor. Reliable and less prone to hardware failure. So less maintenance is required. Reduce computational time from milliseconds to microseconds. Better portability & Wide commercial use. Less heat generated. Programming became more time-efficient since Assembly or Symbolic language was used. Disadvantages: 1. Air conditioning required. 2. Manual assembly of individual components into a functioning unit was required. 3. Commercial production was difficult and costly. 21. Computer Generations Third Generation Computer (1964-1971): The development of integrated circuit by jack kilby was the hallmark of the third generation of computers. Punched cards and printouts gave way to devices like keyboards and monitors Easier for the user to interact with the computer. Existence of an operating system allowed the device to run various applications For the first time, computers were being widely used in business for areas like: accounting, billing etc. Were substantially smaller and cheaper than their predecessors. Example: - NCR 395, B6500. Advantages: Based on Integrated Circuit(IC). Reduce computational time from microsecond to nanoseconds. Better portable and reliable than 2nd generation computers. Consume less power and generated less heat. Maintenance cost was quite low since hardware rarely failed. Disadvantages: Highly sophisticated technology required for the manufacture of IC chips. 22. Computer Generations Fourth Generation computer (1971 to present): Revolution in computer hardware came about which could shrink the computer logic circuitry and its components using the large scale integration (LSI) technology. Hundreds of components could now fit onto a single chip. In the 1980s, Very Large Scale Integration (VLSI) squeezed hundreds of thousands of components onto a single chip. Introduction of Personal Computers (PCs) programmable machines that are small enough and inexpensive so that these can be purchased and used by individuals. Companies like apple computers and IBM introduced very successful pcs. First memory chip was constructed in 1970 and could hold 256 bits. Example: APPLE-II, CRAY-I Advantages: Smallest in size because of high component density. Very reliable. Much faster in computation than previous generation. Heat generated is negligible. So, no air conditioning required in most cases. Hardware failure is negligible and hence minimal maintenance is required. Easily portable because of their small size. Totally general purpose. Minimal labor and cost involved at assembly stage. Cheapest among all generations. Microprocessor based system. Disadvantage: Highly sophisticated technology required for the manufacture of LSI chips. 23. Computer Generations Fifth Generation Computers (Present and Beyond): The goal is to develop devices that are capable of learning and responding to natural language input. Such a computer would learn from his mistakes and possess the skill of experts. This generation of computers is using new technologies Large scale integration, along with new programming languages and will be capable of Amazing feats such as voice recognition. It can be characterized by: Artificial intelligence: it refers to series of technologies to simulate human behavior like thinking, speaking and reasoning. Parallel processing: refers to the computers processing several instructions at once at the same time using multiple processors. 24. Classification of Computers On the basis of Technology Analog Computer Digital Computer Hybrid Computer On the basis of Purpose General Purpose Special Purpose On the basis of Storage Capacity, Size & Computational Speed Micro Computer Mainframe Mini Computer Super Computer 25. Classification of Computers Analog Computer: They are used to process analog data. Analog data is of continuous nature and which is not discrete or separate. Such type of data includes temperature, pressure, speed weight, voltage, depth etc. These quantities are continuous and having an infinite variety of values. Digital Computer: It can be used to process numeric as well as non-numeric data. It can perform arithmetic operations like addition, subtraction, multiplication and division and also logical operations. Most of the computers available today are digital computers. Hybrid Computer: A hybrid is a combination of digital and analog computers. It combines the best features of both types of computers, i-e. It has the speed of analog computer and the memory and accuracy of digital computer. 26. Classification of Computers General Purpose Computer: Most computers in use today are General-Purpose computers , those built for a great variety of jobs. By using a general purpose computer and different software, various tasks can be accomplished, including writing and editing , manipulating facts in a data base, tracking manufacturing inventory, making scientific calculations, or even controlling organizations security system, electricity consumption, and building temperature. Specific Purpose Computer: A Special-Purpose Computer are designed to be task specific and most of the times their job is to solve one particular problem. They are also known as dedicated computers. Such a computer system would be useful in playing graphic intensive Video Games, traffic lights control system, navigational system in an aircraft, weather forecasting, satellite launch / tracking, oil exploration etc. 27. Classification of Computers Super Computer: Supercomputer is the most powerful and fastest, and also very expensive. It was developed in 1980s. It is used to process large amount of data and to solve the complicated scientific problems. It can perform more than one trillions calculations per second. It has large number of processors connected parallel. So parallel processing is done in this computer. Super computer are mainly used for: Nuclear energy research Aircraft design Automotive design The examples of supercomputers are CRAY-1, CRAY-2, Control Data CYBER 205 and ETA A-10 etc. Drawbacks Operating super computer requires highly qualified staff. Experts are required for such computer engineering. They are sensitive to temperature, humidity & dust. Non-portability & large size 28. Classification of Computers Mainframe Computer: Mainframe computers are also large-scale computers but supercomputers are larger than mainframe. It requires a very large clean room with air-conditioner. Large mainframe systems can handle the input and output requirements of several thousands of users. For example, IBM, S/390 mainframe can support 50,000 users. There are basically two types of terminals used with mainframe systems:- Dumb Terminal: Dumb terminal does not have its own CPU and storage devices. This type of terminal uses the CPU and storage devices of mainframe system. Intelligent Terminal: Intelligent terminal has its own processor and can perform some processing operations. Drawbacks Operating super computer requires highly qualified staff. Experts are required for such computer engineering. They are sensitive to temperature, humidity & dust. Non-portability & large size 29. Classification of Computers Micro Computer: The microcomputers are also known as personal computers or simply PCs. The IBMs first microcomputer was designed in 1981 and was named as IBM-PC. The most popular types of personal computers are the PC and the Apple. These two types of computers also use different operating systems. PC and PC-compatible computers use the Windows operating system while Apple computers use the Macintosh operating system (MacOS). Desktop Computer: a personal or micro-mini computer sufficient to fit on a desk. Laptop Computer: a portable computer complete with an integrated screen and keyboard. It is generally smaller in size than a desktop computer and larger than a notebook computer. Palmtop Computer/Digital Diary /Notebook /PDAs: a hand- sized computer. Palmtops have no keyboard but the screen serves both as an input and output device. 30. Classification of Computers Mini Computer: These are smaller in size, have lower processing speed and also have lower cost than mainframe. These computers are known as minicomputers because of their small size. The capabilities of a minicomputer are between mainframe and personal computer. Minicomputers are commonly used as servers in network environment. The first minicomputer was introduced in the mid-1960s by Digital Equipment Corporation (DEC). Drawbacks Cannot connect all hardware devices Cannot execute all languages and softwares 31. Distributed Computers Distributed computing exploits a network of many computers, each accomplishing a portion of an overall task, to achieve a computational result much more quickly than with a single computer. Distributed computing also allows many users to interact and connect openly. The segment of the Internet most people are most familiar with, the World Wide Web, is also the most recognizable use of distributed computing in the public arena. Another type of distributed computing is known as grid computing. Grid computing consists of many computers operating together remotely and often simply using the idle processor power of normal computers. 32. Parallel Computers Parallel computing is the simultaneous use of multiple processors (CPUs) to do computational work. Some operations, however, have many steps that do not have time dependencies and can therefore be broken up into multiple tasks to be executed simultaneously. Parallel computations can be accomplished on shared- memory systems with multiple CPUs. Organizing the concurrent work of the multiple processors and synchronizing the results are handled by program calls to parallel libraries; these tasks usually require parallel programming expertise. 33. Components of a Computer A typical computer system has Input Unit Central Processing Unit Memory Unit Output Unit. This is also known as Von Neumann Architecture of the computer 34. Components of a Computer Input Unit: The input unit links the external environment with the computer system. Data and Instructions are given as input. The input to the computer can be made by keyboard, mouse etc. All the data supplied to the computer is transformed into the binary codes. Unit called input interface accomplishes this transformation. The various input devices are: Keyboard, Mouse, Joy stick, Light Pen, Punched Cards, Optical Mark Reader, Magnetic Tape, and Optical Character Reader. 35. Components of a Computer Output Unit: It links the computer with the external environment. It supplies information and results of computation to the outside world. The results produced are in the binary form. Before supplying the results to the outside world, it must be converted to human readable form. Unit called output interface accomplishes this task. The various output devices are: monitor, printer, and plotter. 36. Components of a Computer Primary Memory : Primary memory is the memory that is used to store the data and the instructions. Every program, that needs to be executed, is to be bought into this primary memory. Primary memory is small and extremely faster. It is volatile in nature i.e. information stored in it is lost as soon as the power is switched off. It is implemented in two types: 1. Random Access Memory (RAM): It is required to provide information to the processor. It is volatile in nature. 2. Read Only Memory (ROM): It stores the initial start-up instructions. It is non volatile in nature. Secondary Memory: Also known for backup storage, it is typically used as a supplement to main storage. It is much cheaper than the main storage. Stores large amount of data and instructions permanently. Hardware devices like magnetic tapes and disks fall under this category. It is slow as compared to primary memory. 37. Components of a Computer Central Processing Unit: The Central Processing Unit (CPU) is the brain of any computer system. As in a human body, the brain, similarly, in a computer system all major computations are made by the CPU and is also responsible for activating and controlling the operations of other units. The Registers, Arithmetic Logical Unit and Control Unit of a computer system are jointly known as the Central Processing Unit (CPU). 1. Control Unit:- The control unit is able to maintain order and direct the operation of the entire system Central nervous system for the computer. Manages and coordinates the entire computer system. Directs the flow of data through the CPU, and to and from other devices. It instructs other parts of CPU on what to do and when to do. Determines what data is needed, where it is stored, where to store and sends the control signals 2. Arithmetic Logic Unit: Circuitry that executes all the arithmetic and logical operations on the data made available to it. ALU comprises two units: Arithmetic Unit: arithmetic calculations such as addition, subtraction, multiplication & division. Logical Unit: logical operations based upon the instructions provided to it. 3. Registers: High speed storage area that temporarily stores data during processing. Stores information such as data, instructions, addresses and intermediate results of calculations. Registers work under the control of control unit to accept, hold, and transfer instruction or data 38. Input Output Devices Input/output devices are required for users to communicate with the computer. input devices bring information INTO the computer and output devices bring information OUT of a computer system. These input/output devices are also known as peripherals since they surround the CPU and memory of a computer system. 39. Input Devices They are electromechanical device that are used for entering the data into computer in the machine under stable form i.e. in binary form. In other words, It accepts data & instruction from the user & other applications. Data input to a computer can be in the form of text, audio etc. All the todays available input devices can be broadly classified into the following categories:- Human Data entry devices: Keyboard Pointing Device(mouse) Picking device(light pen, touch screen) Source data entry devices: Audio input-Speech recognition Video Input-Digital camera Optical scanner-OCR, MICR, OMR. 40. Input Device: Keyboard Device The most commonly used input device is the keyboard on which data is entered by manually keying in or typing certain keys. A keyboard typically has 101 or 105 keys. Function Keys Numeric Keypad Cursor Movement Keys Alphanumeric Keypad/ Special-function Keys 41. Input Device: Point & Draw Device Mouse: The mouse is a common pointing small hand-held input device having 2-3 buttons on upper-side along with a wheel that you can roll over a hard, flat surface It is .used to point to a particular place on the screen and select in order to perform one or more actions. Types Of Mouse: Physical Mouse: I t has a rubber ball on the bottom side that protrudes when the mouse is moved .It require a smooth, dust free surface such as mouse pad on which its rolled. Optical Mouse: It uses led to detect the movement of mouse. It requires an opaque flat surface underneath it. 42. Input Device: Point & Draw Device Joystick(A Screen-pointing Device): The joystick is a vertical stick which moves the graphic cursor in a direction the stick is moved. It typically has a button (also called as triggers)on top that is used to select the option pointed by the cursor. Joystick is used as an input device primarily used with video games, training simulators and controlling robots. Light Pen: It is a pen shaped device used to select objects on a display screen. It is quite like the mouse (in its functionality) but uses a light sensitive detector to move the pointer and select any object on the screen by pointing to the object. Users of Computer Aided Design (CAD) applications commonly use the light pens to directly draw on screen. 43. Input Device: Data Scanning Devices Scanner: Scanner is an input device used for direct data entry from the source document into the computer system. It converts the document image into digital form so that it can be fed into the computer. Types of scanner Flatbed scanners: also called desktop scanners, are the most versatile and commonly used scanners. It provide high quality scan in a single pass. Its a box-shaped machine similar to a photocopy machine &has a glass top & a lid that covers the glass. Used to scan full page documents. Handheld scanners: use the same basic technology as a flatbed scanner, but rely on the user to move them instead of a motorized belt. This type of scanner typically does not provide good image quality. However, it can be useful for quickly capturing text. 44. Input Device: Data Scanning Devices MICR: Magnetic Ink Character Recognition is a character recognition system that uses special ink usually iron oxide and characters. When a document that contains this ink needs to be read, it passes through a machine, which magnetizes the ink and then translates the magnetic information into characters. MICR technology is used by banks. MICR codes can be easily read by humans. 45. Input Device: Data Scanning Devices OCR: Optical character recognition is the mechanical or electronic translation of scanned images of handwritten, typewritten or printed text into machine-encoded text. It is widely used to convert books and documents into electronic files. An OCR system enables you to take a book or a magazine article, feed it directly into an electronic computer file, and then edit the file using a word processor. All OCR systems include an optical scanner for reading text, and sophisticated software for analyzing images. OCR is already being used widely in the legal profession 46. Input Device: Data Scanning Devices OMR: Optical Mark Recognition is the process of capturing human-marked data from document forms such as surveys and tests. Optical Mark Reading (OMR) is one of the fastest and safest methods for data-entry. OMR is a great time-saving process in collecting data but can also create a huge headache if not done correctly. Advantages of OMR-Technology Simplicity Functionality Speed Flexibility 47. Input Devices Bar-code reader: Data coded in the form of small lines (known as bars) are known as bar codes. Bar codes represent alphanumeric data by a combination of adjacent vertical lines(bars) by varying their width and the spacing between them. They are particularly used for unique identification of all types of goods, books, postal packages, badges, tags, etc. A bar-code reader uses a laser-beam scanning technology. Electronic Card Reader: It is connected to a computer, is used to read the data encoded on an electronic card and transfer it to the computer for further processing. Depending on the manner in which data is encoded, electronic card are of following two types: Magnetic strip cards:- These cards have a magnetic strip on their back. The data to be encoded on the card is stored on the magnetic strip. Smart Card:- Smart cards have a built-in microprocessor chip instead of the magnetic strip. 48. Input Devices Voice Recognition Device/Speech Recognizer: It is the technology by which sounds, words or phrases spoken by human are converted into digital signal & these signals are then transformed into computer Text. It accepts the spoken word through microphone & convert them into binary form of 1s & 0s. Thus they make computers much easier to use. Voice recognition system is normally classified into the following 2 categories:- Speaker-dependent: Most voices recognition system of are speaker-dependent. That is they can recognize the speech of only a single individual or a few individuals. Speaker-Independent: Speaker-independent voice recognition systems can recognize words spoken by anyone. 49. Output Devices Output devices are an electromechanical device that accepts data from a computer and then processed the data & display it in a form suitable for use by the outside world (the user). Output generated by output devices is classified into following 2 types:- Soft-copy:- The electronic version of an output which usually resides in a computer memory is known as soft copy. Example-Monitors display Hard-copy: - It is the Physical form of output It refers to the recorded information copied from a computer onto a paper. Example-Printout obtained from printer 50. Output Devices: Monitors Monitors produce soft-copy output. Two basic types of monitor used today 1. Cathode Ray Tube (CRT) Monitor 2. Flat-panel Monitor 1. CRT (Cathode Ray Tube): Monitor is an output device that resembles the television screen and uses a Cathode Ray Tube (CRT) to display information. Like the television, monitors are also available in different sizes. Flat-panel Monitor: The display technologies used by flat-panel monitors include liquid crystal display (LCD), electro-luminescent display (ELD). LCD was introduced in the 1970s and is now applied to display terminals also. Its advantages like low energy consumption, smaller and lighter have paved its way for usage in portable computers (laptops). The flat-panel display are divided into two categories: Emissive Displays - The emissive displays are devices that convert electrical energy into light. Example are plasma panel and LED (Light- Emitting Diodes). Non-Emissive Displays - The Non-emissive displays use optical effects to convert sunlight or light from some other source into graphics patterns. Example is LCD (Liquid-Crystal Device) 51. Output Devices: Printers Printers are used to produce paper (commonly known as hardcopy) output. There are two types of printers: Impact Printers Non-Impact Printers Printers Impact Printers Non-Impact Printers Character Printers Line Printers Dot-Matrix Printers Daisy Wheel Printers Chain Printers Drum Printers Laser Printers Inkjet Printers 52. Output Devices: Printers Impact Printers: Use the typewriting printing mechanism wherein a hammer strikes the paper through a ribbon in order to produce output. The ink ribbon is pressed against the paper, marking the page with the appropriate character, dot, line, or symbol. Characteristics of Impact Printers are the following: Very low consumable costs Impact printers are very noisy Useful for bulk printing due to low cost There is physical contact with the paper to produce an image These printers are of two types: Character printers Line printers 53. Output Devices: Printers Character Printers: Character Printers are printers, which print one character at a time. These are of further two types: Dot Matrix Printer (DMP) Daisy Wheel Dot Matrix Printer: Dot-matrix printers print about 40-300 characters per second (cps) and can print some graphics, although the reproduction quality is poor. Color ribbons are available for limited use of color. Dot-matrix printers are noisy, inexpensive, and they can print through multipart forms, creating several copies of a page at the same time. Advantages Inexpensive Widely Used Other language characters can be printed Disadvantages Slow Speed Poor Quality 54. Output Devices: Printers Daisy Wheel: A type of printer that produces letter- quality type. A daisy-wheel printer works on the same principle as a ball-head typewriter. To print a character, the printer rotates the disk until the desired letter is facing the paper. Then a hammer strikes the disk, forcing the character to hit an ink ribbon, leaving an impression of the character on the paper. Advantages More reliable than DMP's Better quality The fonts of character can be easily changed. Disadvantages Slower than DMP's Noisy More expensive than DMP's 55. Output Devices: Printers Line Printers: A high-speed printer capable of printing an entire line at one time. A fast line printer can print as many as 3,000 lines per minute. The disadvantages of line printers are that they cannot print graphics, the print quality is low, and they are very noisy. These are of further two types: Drum Printer Chain Printer Drum Printer: An impact printer in which a complete set of characters for each print position on a line is on a continuously rotating drum behind an inked ribbon, with paper in front of the ribbon; identical characters are printed simultaneously at all required positions on a line, on the fly, by signal-controlled hammers Advantages Very high speed Disadvantages Very expensive Characters fonts can not be changed Chain Printer: The print element in a chain printer is a metallic band or chain containing the embossed characters that rotates horizontally in front of paper. A complete chain consists of the five sections; each section consists of 48 characters. As the print chain rotates, properly timed print hammers strike the paper along with linked ribbon, against the proper character on the chain as it passes. Chain printer are one of the fastest impact printers Advantages Character fonts can easily be changed. Different languages can be used with the same printer. Disadvantages Noisy Do not have the ability to print any shape of characters. 56. Output Devices: Printers Non-impact Printers: Non-impact printers do not touch the paper while printing. Nonimpact printers form characters and images without direct physical contact between the printing mechanism and the paper. They use chemical, heat or electrical signals to etch the symbols on paper. These printers are of two types: Laser Printers Inkjet Printers Characteristics of Non-impact Printers: Faster than impact printers. They are not noisy. High quality. Support many fonts and different character size. 57. Output Devices: Printers Laser Printers: Like a dot-matrix printer, a laser printer creates images with dots. However, as in a photocopying machine, these images are created on a drum, treated with a magnetically charged ink-like toner (powder), and then transferred from drum to paper. Advantages Very high speed. Very high quality output. Gives good graphics quality. Supports many fonts and different character sizes. Disadvantage Expensive. Cannot be used to produce multiple copies of a document in a single printing. Inkjet Printers: Like laser and dot-matrix printers, ink-jet printers also form images with little dots. Ink-jet printers spray small, electrically charged droplets of ink from four nozzles through holes in a matrix at high speed onto paper. Ink-jet printers can print in color and are quieter and much less expensive than a color laser printer. Advantages High quality printing More reliable Disadvantages Expensive as cost per page is high Slow as compared to laser printer 58. Difference between Impact and Non-Impact printer Impact printer:- Non-Impact Printer:- It prints characters or images by striking print hammer against an inked ribbon. Its speed is lower. Its print quality is poor. It normally uses continuous paper sheet. It uses inked ribbon for printing. It generates noise during printing. It is less expensive. Dot matrix is an example. It prints character or image without striking the paper. Its speed is faster. Its print quality is higher. It normally uses individual paper sheet. It doesnt generate noise during printing. It uses toner or cartridges for printing. It is more expensive. Laser and Ink Jet are an example. 59. Output Devices: Plotter Plotters are used to print graphical output on paper. Plotters are ideal output devices for architects, engineers, city planners and others who need to routinely generate high precision, hard-copy graphic output of widely varying sizes. Two commonly used types of plotter are:- 1. Drum Plotter 2. Flatbed plotter Drum Plotter: In a drum plotter the paper on which the design has to make is placed over a drum that can rotate in both clockwise and anti-clockwise directions to produce vertical motion. Flatbed plotter: A flatbed plotter plots a design or graph on a sheet of paper that is spread and fixed over a rectangular flatbed table. 60. Computer Memory Memory Cell Building block of computer data storage. Entire RAM is divided into a number of equal parts, known as memory cells. Each memory cell can store one-byte of data. Each memory cell has unique address. Units to measure Computer memory: Bit: smallest unit of information. It can hold either 0 or 1. Byte: A unit of 8 bits is known as a byte. Kilobyte: 1024 bytes Megabyte: 1024 kilobyte Gigabyte: 1024 Megabyte. Terabyte: 1024 gigabyte. 61. Memory Organization The computer memory is a temporary storage area. It holds the data and instructions that the Central Processing Unit needs. Before a program can be run, the program is loaded from some storage medium into the memory. This allows the CPU direct access to the program. Memory is a need for any computer. There are two types of computer memory: Primary Secondary. Primary memory is accessible directly by the processing unit. RAM is a model of primary memory. As soon as the computer is switched off the contents of the primary memory is lost. You can store and retrieve data much quicker with primary memory compared to secondary memory. Secondary memory such as floppy disks, magnetic disk, etc., is located outside the computer. Primary memory is more expensive than secondary memory. Because of this the size of primary memory is less than that of secondary memory. 62. Primary Memory 63. Primary Memory Characteristic of Main Memory These are semiconductor memories. It is known as main memory. Usually volatile memory. Data is lost in case power is switched off. It is working memory of the computer. Faster than secondary memories. A computer cannot run without primary memory. Primary Memory can be divided into two types Random Access Memory (RAM) Read Only Memory (ROM). 64. Primary Memory: RAM RAM :RAM is a memory scheme within the computer system responsible for storing data on a temporary basis, so that it can be promptly accessed by the processor as and when needed. It is volatile in nature, which means that data will be erased once supply to the storage device is turned off. RAM is of two types: Static RAM (SRAM) Dynamic RAM (DRAM) Characteristics of the Static RAM: It has long data lifetime There is no need to refresh Faster Used as cache memory Large size Expensive High power consumption Characteristics of the Dynamic RAM: It has short data lifetime Need to refresh continuously Slower as compared to SRAM Used as RAM Lesser in size Less expensive Less power consumption 65. Primary Memory: ROM Unlike RAM, ROM is a permanent form of storage. ROM stays active regardless of whether power supply to it is turned on or off. The ROM memory used in modern computers is pre-programmed by the circuit manufacturer and cannot be altered by the user. Types of ROM Masked ROM: They are hard-wired devices that contain a pre-programmed set of data and instructions. PROM (Programmable Read only Memory): PROM is read-only memory that can be modified only once by a user. EPROM (Erasable and Programmable Read Only Memory): The EPROM can be erased by exposing it to ultra- violet light for a duration of up to 40 minutes. EEPROM (Electrically Erasable and Programmable Read Only Memory): The EEPROM is programmed and erased electrically. It can be erased and reprogrammed about ten thousand times. 66. Secondary Memory Characteristics of Secondary Memory These are magnetic and optical memories. It is known as backup memory. It is non-volatile memory. Data is permanently stored even if power is switched off. It is used for storage of the data in the computer. Computer may run without secondary memory. Slower than primary memories. Depending on the access mechanism used we categorized the secondary memory into two types:- Sequential Access Storage Devices (SASD): It is a class of data storage devices that read their data in sequence and the time for access depends on the location of the data desired. Direct Access Storage Devices (DASD): are also called random-access devices. It allows stored data to be accessed in any order 67. Secondary Memory Secondary Storage Device Sequential Access Storage Device Direct Access Storage Device Magnetic Tape Magnetic Disk Optical Disk Hard Disk Floppy Disk CD-ROM WORM CD-RW DVD 68. Secondary Memory: Magnetic Tape Magnetic tape is a form of auxiliary memory which is more commonly used as back up storage. Data is represented as magnetized and non-magnetized spots representing 1s and 0s. Because of continuous length read/write head cannot jump to the desired location, thus tape must be read or written sequentially. In magnetic tape the records are separated by blank spaces on the tape, called Inter record gaps (IRG). Uses Magnetic tapes are used for the following applications: For taking backups of data that re stored on an on-line storage device (i.e disks) so that data can be retrieved from the backup if data on the disk is lost accidently. Archiving of data which may be required rarely. Magnetic tapes are generally used for distribution of software by vendors. Magnetic tapes are used for applications which require sequential data processing. Advantages High Storage Capacity Low Cost Reusability Easy to handle Portability Limitations Magnetic tape is not suitable for applications which require random access of data. Tape must be stored in dust-free and moisture free environment. It needs to be labeled in order to avoid ambiguity. 69. Secondary Memory: Magnetic Disk Magnetic disks are most commonly used direct access storage device. A magnetic disk's medium contains iron particles. Each particle's direction represents a 1 (on) or 0 (off), representing each bit of data that the CPU can recognize. The most commonly used magnetic disks are floppy disks and hard disks. Floppy Disks: A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles. They are read and written by a floppy disk drive (FDD). Invented by IBM, floppy disks in 3.5-inch (89 mm), 5.25-inch (133 mm) and 8- inch (200 mm) forms Floppy disks store less data than a CD-ROM or USB flash drive. Hard Disk: A magnetic disk on which you can store computer data. Hard disks hold more data and are faster than floppy disks. 70. Secondary Memory: Magnetic Disk Uses: Magnetic Disk is used for application that requires random data processing. As a backup device for off-line data storage. Archiving of data that are not used frequently but may be used occasionally. Transferring of data & programs between two computers that are not linked together. Advantages: Magnetic Disk support direct access of data making them more suitable for a wider range of application. Floppy disk being compact in size & light in weight are easy to handle & store. An additional cost benefit is that magnetic disk can be erased & reused many times. Magnetic disk is suitable for both on-line & off-line storage of data. Due to random access property, magnetic disk are often used by multiple users simultaneously as a shared device. Limitations Use of magnetic disk is less efficient than magnetic tape for sequential applications. It is more difficult to maintain security of information stored on those magnetic disks that are used as shared. Some type of magnetic disks easily portable as magnetic tapes. They must be stored in a dust-free environment. 71. Secondary Memory: Optical Disk Optical disk is flat, circular plastic plate coated with a thin layer of metal like aluminum, gold or silver on which data may be stored from which data is read or written into through a laser beam. These disks are capable of storing enormous amount of data in a limited amount of space. Example-CD,DVD Optical disk comes in various sizes and capacity. A CD can store 600-700 MB of data while DVD can store data in GB. Read-Only Discs: CD-ROM and DVD-ROM Discs CD-ROM: A CD-ROM is a CD that contains computer data, which cannot be rewritten. CD-ROM is the most commonly used optical storage technology. Data is stored on the disc as a series of light and dark pits. DVD-ROM: DVD-ROM is an optical disc storage media format that can be used for data storage, which includes movies with high video and sound quality. These DVDs are read-only disks that have storage capacity for 133 minutes of high quality video. Rewritable Discs: CD-RW, DVD-RW The newer rewritable discs can be recorded on, erased, and overwritten just like a magnetic disk. The most common types of rewritable optical media are CD- RW, DVD-RW, and DVD+RW discs. CD-RW discs are written to using a CD- RW drive and can be read by most CD and DVD drives. DVD-RW discs and DVD+RW discs are recorded using a DVD-RW drive or DVD+RW drive 72. Secondary Memory: Optical Disk Advantages of Optical Disks Cost per bit of storage for optical disks is very low They have data storage life in excess of 30 years. Due to their compact size and light weight, they are easy to handle and store. Limitations of Optical Disks CD-ROM disks are read only storage medium. Data once recorded cannot be erased. Hence they cannot be reused. Data access speed for optical disks is slower than magnetic disks. Since optical disk is a removable media it is prone to scratches, dust etc. 73. Physical devices used to construct memory A Capacitor Storage Cell: A capacitance can be in two states: a state in which it is fully charged, and another in which it is fully discharged. The charged state is 1 state, and the discharged state is 0 state. If a 1 is to be written in the cell of, a voltage V is applied to the input line and a write signal is applied to write line. The write signal closes switch S1 and the voltage V applied to input charges the capacitance, thereby storing 1 is it. The state of capacitor is read by applying a signal to the read line. 74. Physical devices used to construct memory A Flip-Flop Storage Cell: A flip-flop is a storage device which uses four semiconductor switches to store either a 0 or a 1. The major advantages of a flip-flop compared to a capacitor are: It takes lesser time to store a bit in it as compared to a capacitor memory cell. The data stored in a cell is not lost with passage of time. There is no need to refresh the memory. The readout from a flip-flop is non-destructive. In other words, when data is read from flip-flop, it is not erased. The major disadvantages of a flip-flop as compared to a capacitor are: Flip-flops are more expensive Flip-flops occupy more space as they use four semiconductor switches. They need continuous application of power to maintain their state. When power fails, the stored data is lost. It is thus volatile. 75. Physical devices used to construct memory A Magnetic Storage Cell: The physical device used as a magnetic storage cell is a magnetic recording surface. If a 1 is to be written on the magnetic surface, a current is sent through a coil wound on a magnetic write head. If a 0 is to be written, the current in the coil is sent in the opposite direction. A Polycarbonate Cell: This cell is used in laser disks or compact disks. The surface of a thin polycarbonate substrate is coated with a shiny material, usually aluminum. Whenever a 1 to be written, the beam is turned on and burns a pit up to the reflective layer. Wherever a 0 is to be written, the laser beam is defocused and no pit is burnt.