FOC001_ Fundamentals of Computer

Hardware and Software 93 are Q, W, E, R, T, Y. The numeric keypad looks like a calculator’s keypad, with its 10 digits and mathematical operators (+, - , *, /) . ? Numeric keys also features NUM LOCK key. (ii) Punctuation keys: All of the keys associated with punctuation such as the comma, period, semicolon, brackets, parenthesis and so on. Also, all of the mathematical operators such as the plus sign, minus sign, and equal sign. (iii) Special keys: He standard keyboard contains special key such as: • Alt key – Short for Alternate, this key is like a second control key. • Arrow Keys – Most keyboards have four arrow keys that enable to move the cursor up, down, right or left. • Backspace key – Deletes the character just to the left of the cursor and moves the cursor to that position. • Caps Lock Key – A toggle key that, when activated, causes all alphabetic characters to be uppercase. • Ctrl key – Short for Control, this key is used in conjunction with other keys to produce control characters. The meaning of each control character depends on which program is running. • Delete Key – Sometimes labeled Del, deletes the character at the current cursor position or the selected object but does not move the cursor. For graphics-based applications, the Delete key deleted the character to the right of the insertion point. • Enter Key – Used to enter commands or to move the cursor to the beginning of the next line. Sometimes labeled Return instead of Enter. • Esc Key – Short for Escape, this key is used to send special codes to devices and to exit (or escape) from programs and tasks. • Function Keys – Special keys labeled F1 to F12. These keys have different meaning depending on which program is running. CU IDOL SELF LEARNING MATERIAL (SLM)

94 Computer Fundamentals Mouse Mouse is a device that controls the movement of the cursor or pointer on a display screen. A mouse is a small object, it can roll along a hard, flat surface. Its name is derived from its shape, which looks a bit like a mouse, its connecting wire that one can imagine to be the mouse’s tail, and the fact that one must make it scurry along a surface. As user move the mouse, the pointer on the display screen moves in the same direction. The computer mouse is considered an input device. With a click of a button, the mouse sends information to the computer. The computer mouse is an interesting device that offers an alternative way to interact with the computer beside a keyboard. A typical mouse has two buttons. At the top of the device you will find a left and right button which allows for “clicks”. There is a scrolling wheel between the two buttons. Fig. 5.5: Mouse Types of Mouse Based on their ports, there are three common types namely: (i) PS/2 mouse (ii) USB mouse (iii) Serial mouse Based on their designs, there are three common types namely: (i) Mechanical mouse: It is a device integrated with an internal metal or rubber ball, which can spin in all directions (left, right, up and down). Thus, the display cursor moves as the mouse detects the direction. The ball in the mechanical mouse spins when it comes in CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 95 contact with surface on which it is placed. A mouse pad should be used under the mouse to run on. (ii) Optomechanical mouse: This type of computer mouse is the same as the mechanical mouse except that it uses optical sensors to the motion of the ball. A mouse pad should be used under the mouse to run on. (iii) Optical mouse: This type of mouse uses a LED sensor for detecting the mouse's movement. This mouse doesn’t have mouse ball and electromechanical transducer. Movement is detected by sensing changes in reflected light, instead of interpreting the motion of a rolling sphere. This type mouse responds more quickly and precisely than the mechanical and optomechanical mouse. An optical mouse does not have moving parts. That is why there is no need of cleaning. Even user don't need a mouse pad. (iv) Wireless mouse: The Mouse without wire or cord is called wireless mouse or cordless mouse. Most wireless mice use radio frequency (RF) technology to communicate information to computer. Digital Camera Images can be input into a computer using a digital camera. The digital camera takes a still photograph, stores it, and then sends it as digital input into the computer. Fig. 5.6: Digital Camera The images are then stored as digital files. These images can then be manipulated in many ways using the various imaging tools available. CU IDOL SELF LEARNING MATERIAL (SLM)

96 Computer Fundamentals Scanner Scanner is an input device that can read text or illustrations printed on paper and translate the information into a form that the computer can use. A scanner works by digitizing an image; dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in (For color and gray scaling, the same principle applies but each box is represented by up to 24 bits). Fig. 5.7: Scanner The resulting matrix of bits, called a bit map, then can be stored in a file, displayed on a screen and manipulated by programs. Optical scanners do not distinguish text from illustrations; they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR) system to translate the image into ASCII characters. Most optical scanners sold today come with OCR packages. Punched Card Punched Cards are still in use as medium for recording data and instructions in the form of punched holes to denote and then they are sequentially read by the card reader. The card reader sends the data and instructions to the CPU to process them. Fig. 5.8: Punched Card CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 97 The punched cards used for data processing are made generally of 80 columns and 12 rows. Today 96 columns cards are available. In these cards a hole is punched to represent the binary 1. The absence of a hole represent binary 0. If a card is punched wrongly, it cannot be corrected. The cards are read by a unit called a card reader. On receiving the command from the control unit the device moves the cards one by one over two sub-devices. One of which, senses the punched holes (0’s and 1’s) and transcribes the pulses to the CPU. Then the output is given as per user specification. Trackball Trackball is another pointing device. Essentially, a it is a mouse lying on its back. To move the pointer, you rotate the ball with your thumb, your fingers, or the palm of your hand. There are usually one to three buttons near to the ball, which you use just like mouse buttons. The advantage of trackballs over mouse is that the trackball is stationary so it does not require much space to use it. In addition, you can place a trackball on any type of surface, including your lap. For both these reasons, trackballs are popular pointing devices for portable computers. Fig. 5.9: Trackball Joystick A lever that moves in all directions and controls the movement of a pointer of some other display symbols. A joystick is similar to a mouse, except that with a mouse the cursor stops moving as soon as you stop moving the mouse. Fig. 5.10: Joystick CU IDOL SELF LEARNING MATERIAL (SLM)

98 Computer Fundamentals With a joystick, the pointer continues moving in the direction the joystick is pointing. To stop the pointer, you must return the joystick to its upright position. Most joysticks include two buttons called triggers. Joysticks are used mostly for computer games, but they are also used occasionally for CAD/CAM systems and other applications. Light Pen Light pen is an input device that utilizes a light-sensitive detector to select objects on a display screen. It is similar to a mouse, except that with a light pen you can move the pointer and select objects on the display screen by directly pointing at the objects with the pen. Fig. 5.11: Light Pen Digitizing Tablet This is an input device that enables you to enter drawings and sketches into a computer. A digitizing tablet consists of an electronic tablet and a cursor or pen. A cursor (also called puck) is similar to a mouse, except that, it has a windows with cross hairs for pinpoint placement and have as many as 16 buttons. Fig. 5.12: Digitizing Tablet A pen (also called a stylus), which looks like a simple ballpoint pen but uses an electronic head instead of ink. The tablet contains electronics that enables it to detect movement of the cursor or pen and translate the movements into digital signals that it sends to the computer. CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 99 For digitizing tablets, each point on the tablet represents a point on the display screen in a fixed manner. This differs from a mouse, in which all movement is relative to the current cursor position. The static nature of digitizing tablets makes them particularly effective for tracing which the pen or cursor acts like a mouse. Digitizing tablets are also called digitizers, graphics tablets, touch tales or simply tablets. Touchpad A small, touch-sensitive pad is used as a pointing device on some portable computers. It is consisting of specialized surface that can translate the motion and position of a user’s fingers to relative position on screen. It is also called trackpad. Fig. 5.13: Touchpad Optical Mark Reader (OMR) Optical marks are commonly used for scoring in tests. It is marked by the person taking the test, and can be read by the optical mark reader. The optical mark reader when online to the computer systems, can read upto 2,000 documents per hour. Seemingly this rate is slow but the fact that transcription has been eliminated, the overall time is less than those of conventional file media. Fig. 5.14: Optical Mark Reader (OMR) CU IDOL SELF LEARNING MATERIAL (SLM)

100 Computer Fundamentals OMR can also be used for such applications as order writing, payroll, inventory control, insurance, questionnaires etc. However, it is to be noted that designing the documents for OMR is rather a tough task. They should be simple to understand otherwise errors may result, more perhaps, than would occur in using traditional source documents and keypunching from them. Handwriting Recognition Device: OCR Often abbreviated OCR, optical character recognition refers to the branch of computer science that involves reading text from paper and translating the images into a form that the computer can manipulate (for example, into ASCII codes). As OCR system enables you to take a book or a magazine article and feed it directly into an electronic computer file. All OCR systems include an optical scanner for reading text, and sophisticated software for analyzing images. Most OCR systems use a combination of hardware (specialized circuit boards) and software to recognize characters, although some inexpensive systems do it entirely through software. Advanced OCR systems can read text in a large variety of fonts, but they still have difficulty with hand written text. The potential of OCR systems is enormous because they enable users to harness the power of computers to access printed documents. It is already being used widely in the legal profession, where searches required hours or days, now can be accomplished in a few seconds. Fig. 5.15: Handwriting Recognition Device: OCR CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 101 Magnetic Ink Character Recognition (MICR) An MICR can identify and decode characters printed with a special ink that contains particles of magnetic material. The reading process is called Magnetic Ink Character Recognition. The major advantage of these characters is that they are machine readable, the process is faster and less error-prone. Since MICR systems can recognize only certain character styles, the characters have to be accurately formed. Fig. 5.16: Magnetic Ink Character Recognition (MICR) MICR employs a system of printed characters which are easily decipherable by human beings as well as a machine reader. They use special printing font to represent characters. In this font, each character is basically composed of vertical bars. This method is primarily used in banking industry and most cheques are now processed under the MICR approach. The data printed across the bottom of a blank cheque are recorded in MICR form: the characters represent the bank on which the cheque is drawn, the customer’s account number and the amount on cheque. The cheques themselves are prepared off-line. When they are originally printed by a printing press, the bank identification number, as well as the data about the customer’s account number are printed simultaneously. The cheques have been cashed or deposited in bank, an operator uses an off-line enclosing machine to encode, in magnetic ink the amount on the cheque’s bottom-right side. CU IDOL SELF LEARNING MATERIAL (SLM)

102 Computer Fundamentals Bar Code Reader You are probably familiar with the bar code readers in supermarkets, bookshops, etc. Bar-code readers are photo electric scanners that read the bar codes, or vertical zebra striped marks, printed on product containers. Supermarkets use a bar code system called the Universal Product Code (UPC). Fig. 5.17: Bar Code Reader The bar code identifies the product to the supermarket’s computer, which has a description and the latest price of the product. The computer automatically tells the PoS (Point of Sales) terminal what the price is. Speech Recognition Device: Microphones A speech recognition program can process the input and convert it into machine-recognized commands. It is also known as Speech Input Device. Fig. 5.18: Speech Recognition Device: Microphones CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 103 Sometimes abbreviated as mic, a microphone is a hardware peripheral originally invented by Emile Berliner in 1877 that allows computer users to input audio into their computers. Webcam A web camera (or webcam) is a real-time camera whose images can be accessed using the World Wide Web, instant messaging or a PC video calling application. Web-accessible cameras typically involve a digital camera which uploads images to a web server, either continuously or at regular intervals. This may be achieved by a camera attached to a PC or by dedicated hardware. Videoconferencing cameras typically take the form of a small camera connected directly to a PC. Fig. 5.19: Webcam As webcam capabilities have been added to instant messaging text chat services such as Yahoo Messenger, AOL Instant Messenger (AIM), Windows Live Messenger and Skype, one-to- one live video communication over the internet has now reached millions of mainstream PC users worldwide. Webcams are being used for security purposes. Businesses are using webcams to monitor and record activity in offices, hallways and warehouses. A webcam alone cannot record video activity. Webcam monitoring software is needed in combination with a webcam to make a complete video security tool. 5.6 Basic Output System Output is anything that comes out of a computer. Output can be meaningful information or gibberish, and it can appear in a variety of forms – as binary numbers, as characters, as pictures, and as printed pages. An output device is any machine capable of representing information from a computer. Output devices include display screens, loudspeakers, printers, plotters, etc. CU IDOL SELF LEARNING MATERIAL (SLM)

104 Computer Fundamentals Monitor A computer monitor, technically termed as visual display unit is an output device that presents the information from the CPU on the screen working as an interface between CPU and the user. A cable connects the monitor to a video adaptor or video card which is set up on the motherboard of the computer. The CPU (Central Processing Unit) sends instruction to the video adaptor telling what needs to be displayed on the screen. The video adaptor converts the instructions into a set of corresponding signals and sends to the monitor. Monitor contains a circuitry that generates the picture on the screen from the set of signals. Fig. 5.20: Monitor The major parameters that measure the performance of a monitor are luminance, contrast ratio, resolution, dot pitch, response time, refresh rate and power consumption. The common problem that arises in monitors is dead pixels, blurred screen, phosphor-burn, etc. Attributes of Monitor (i) Size: The most important aspect of a monitor is its screen size. A typical size for small VGA monitor is 14 inches.. CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 105 (ii) Resolution: The quality of a display monitor depends on its resolution. In general, higher resolution will leads to clear picture. Fig. 5.21: CRT Monitor Fig. 5.22: LCD Monitor Fig. 5.23: LED Monitor (iii) Convergence: Each pixel is composed of three colours namely red, blue and green. If the dots are not converged properly, the pixel will appear blue. Types of Computer Monitor Most people use computer monitors daily at work and at home. And while these come in a variety of shapes, designs and colors, they can also be broadly categorized into three types. 1. CRT Monitor: CRT stands for Cathode Ray Tube. These monitors employ CRT technology, which was used most commonly in the manufacturing of television screens. CRT stands for Cathode Ray Tube. A cathode ray tube is basically a vacuum tube containing an electron gun at one end and a fluorescent screen at another end. These guns generate red, green and blue (RGB) colors which are generated other color with a combination of these three colors. Nowadays, most of the CRT monitors are replaced by LCD and LED Monitors. The main disadvantages are heavy weight, occupy more place, high power consumption, high radiation and supports low resolution. 2. Flat-panel Monitor: Flat-panel monitor is a thin screen display found on all portable computers and is the new standard for desktop computers. Flat panel displays use liquid- crystal display (LCD) or light-emitting diode (LED) technology to make them much lighter and thinner compared to a traditional monitor. Actually there are no differences between LCD and LED monitors but better picture quality in LED monitors. CU IDOL SELF LEARNING MATERIAL (SLM)

106 Computer Fundamentals Printers Printer is a device that prints text or illustrations on paper and in many cases on transparencies and other media. There are many different types of printers. In terms of the technology utilized, printers fall into the following categories. Printers are output devices that print documents and reports. Printers are of two major categories: (a) IMPACT (b) NON-IMPACT Fig. 5.24: Printers (a) Impact Printers Impact printers are two types. They are: (i) Character Printers Character Printers print character by character. Two commonly used character printers are Dot Matrix and Daisy Wheel Printers. Dot Matrix are so called because the characters printed are made up of dots. They typically have a speed of around 200 cps (Character per second) Daisy Wheel Printers are so called because the printing mechanism is a wheel with radial spokes. At the end of each spoke is a block with a character embossed on it. In a daisy wheel printer, characters are fully formed unlike those in dot-matrix printers. Hence they produce a higher quality print than a dot matrix printer. They typically have a speed of about 35 CPS. They print by spraying patterns of ink on to paper from a nozzle on jet and have a speed of about 90 CPS. Ink-Jet produce a high quality of print and hence are popular in offices. CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 107 Fig. 5.25: Character Printers Ink-Jet Printer Ink-jet printers work by spraying ionized ink at a sheet of paper. Magnetized plates in the ink’s path direct the ink onto the paper in the desired shapes. Ink-jet printers are capable of producing high quality print approaching that produced by laser printers. A typical ink-jet printer provides a resolution of 300 dots per inch, although some newer models offer higher resolutions. Fig. 5.26: Ink-jet Printer In general, the price of ink-jet printers is lower than that of laser printers. However, they are also considerably slower. The drawback of ink-jet printers is that they required a special type of ink that is apt to smudge on inexpensive copier paper. Because ink-jet printers require smaller mechanical parts than laser printers, they are especially popular as portable printers. Daisy Wheel Printer ‘Daisy Wheel’ printers work in a similar manner to an electronic typewriter. The major difference is that they use a new type of printing element called a ‘daisy wheel’. This is a moulded metal or plastic disk shaped printing element which looks very much like a daisy, hence the name. CU IDOL SELF LEARNING MATERIAL (SLM)

108 Computer Fundamentals Fig. 5.27: Daisy Wheel Printer The main element in the Daisy wheel printer consists of a circular fan of metal or plastic petals radiating from a central hub. A single character is embossed on each petal. An electromechanical hammer slams the proper daisy wheel into contact with the ribbon, which transfers its inked impression on to the surface of the paper. Dot-matrix Printer Dot-matrix printers create characters by striking pins against an ink ribbon. Each pin makes a dot, and combinations of dots form characters and illustrations. Fig. 5.28: Dot-matrix Printer Dot-matrix printers are inexpensive and relatively fast, but they do not produce high quality output, compared to laser and ink-jet printers, dot-matrix printers are notorious for making a racket. Although the prices of laser and ink-jet printers are dropping rapidly, dot-matrix printers are still cheaper to operate. In addition, since they are impact printers, the dot matrix printers can print to multi-page forms (that is, carbon copies), something laser and ink-jet printers cannot do. CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 109 Fig. 5.29: Dot-matrix Printer Mechanism Drum Printer The Drum Printer consists of a metal drum that rotates at a constant rate. All the characters to be printed are embossed on the rotating metal drum in horizontal rows, a row of As, a row of Bs, a row of Cs and so on. When a particular letter passes the proper part on the paper, a small electromechanical hammer slams the paper into contact with its inked metal impression. Usually about 120 hammers are arranged side by side. Each one serves particular part along the line. Fig. 5.30: Drum Printer On each line all the As are printed first, then all the Bs, then all the Cs and so on until the entire line is completed. The paper then advances upward one-line and the procedure is repeated. Chain Printer The chain printer also prints a line at a time. It resembles a bicycle chain that rotates at a constant speed. Each link of the chain is embossed with a single letter, number or special character. Depending on the number of different characters to be printed, the alphabet may be rimmed around the periphery of the chain. CU IDOL SELF LEARNING MATERIAL (SLM)

110 Computer Fundamentals Thus, in a single revolution of the chain, as many as five lines can be printed. Two rows of holes along the outer edges allows the device to advance the paper immediately after each line has been printed. Fig. 5.31: Chain Printer (ii) Line Printers These are more expensive than character printers. However, they are much faster. Typically, line printers come in speeds of 300, 600, 900, 1200, 1500 lines per minute (LPM). They are used for voluminous routine jobs like preparing electricity, water, telephone bill, shares printing, etc. Fig. 5.32: Line Printers (b) Non-impact Printers These include Thermal and Laser printers. The technique used is to send light beams to electrically charge a drum surface which attracts lower ink particles and these are then deposited on paper to form an image. Laser printers are the most expensive of the above stated printers. These are Page Printers which print at the speed of Pages Per Minute (PPM). Laser printers are silent, give a very CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 111 high quality permit and have capacity of handling voluminous printing jobs very rapidly. Speeds exceeding 20,000 LPM (lines/minute) are fairly common for Laser Printers. Also, they are popular in Printing Industries for Desk Top Publishing (DTP). Thermal Printer Thermal printers are printers that produce images by pushing electrically heated pins against special heat-sensitive paper. These printers are inexpensive and are used in most calculators and many fax machines. They produce low-quality print, and the paper tends to curl and fade after a few weeks or months. Fig. 5.33: Thermal Printer • Quality of Type: The output produced by printers is said to be either letter quality (as good as a typewriter), near letter quality, or draft quality. Only daisy-wheel, ink-jet and laser printers produce letter-quality type. • Speed: Measured in characters per second (cps) or page per minute (ppm), the speed of printers varies widely. • Impact or Non-impact: Impact printer includes all printers that work by striking an ink ribbon. • Graphics: Some printers (daisy-wheel and line printers) can print only text. Other printers can print both text and graphics. • Fonts: Some printers, notably dot-matrix printers, are limited to one or a few fonts. In contrast, laser and ink-jet printers are capable of printing an almost unlimited variety of fonts. Daisy-wheel printers can also print different fonts, but you need to change the daisy wheel, making it difficult to mix fonts in the same document. CU IDOL SELF LEARNING MATERIAL (SLM)

112 Computer Fundamentals Laser Printer Laser printer utilizes a laser beam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and processor. This is also the way copy machines work. Fig. 5.34: Laser Printer Because an entire page is transmitted to a drum before the toner is applied, laser printers are sometimes called page printers. There are two other types of page printers that fall under the category of laser printers even though they do not use laser at all. One uses an array of LEDs to expose the drum and the other uses LCDs. The drum is changed once. However, they both operate like a real laser printer. Plotter Plotter is a device that draws pictures on paper based on commands from a computer. Plotters differ from printers in that they draw lines using a pen. As a result, they can produce continuous lines, whereas printers can only simulate lines by printing a closely spaced series of dots. Multicolour plotters use different-colored pens to draw different colours. Fig. 5.35: Plotter CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 113 In general, plotters are considerably more expensive than printers. They are used in engineering applications where precision is mandatory. Projector A projector is a specialized computer display that projects an enlarged image on a movie screen. Such devices are commonly used in presentations. Projectors are widely used for conference room presentations, classroom training, home theatre and live events applications. Fig. 5.36: Projector A Digital projector, also known as a Video Projector, is using for displaying video, images or computer data on a screen or other flat surface. It is now popular for “home theater” applications. The cost of a device is not only determined by its resolution, but also by its light output, acoustic noise output, contrast, and other characteristics. Headphone Headphones give sound output from the computer. Headphone is a mini speaker that is usually used to listen to music and/or movie or video. This product is usually attached to the ears and connected to digital devices, like MP3 Player, computer, radio, and iPod. These are also known as earspeakers, earphones or colloquially. Fig. 5.37: Headphone CU IDOL SELF LEARNING MATERIAL (SLM)

114 Computer Fundamentals Speaker Speakers in or on a computer are used to output sounds from the system unit. There are both internal and external speakers that can be used on a computer. Speakers are connected to a computer's sound card. They receive audio input from the computer's sound card and produce audio output in the form of sound waves. Most computer speakers are active speakers, meaning they have an internal amplifier which allows you to increase the volume, or amplitude, of the sound. Speakers typically come in pairs, which allows them to produce stereo sound. This means the left and right speakers transmit audio on two completely separate channels. Signal Volume indicator balance LED control Power Fig. 5.38: Speaker swich Computer Output Microfilm Computer Output Microfilm is a system that converts stored data directly to microfilm or microfiche. Information is recorded on a roll of film. COM technology, with a history that dates back to the first patent for microphotography in 1839, has been used for document and newspaper archival since the 1920s. COM systems are still used today, mostly by organizations which need to store payroll, accounting, insurance, inventory or employee data. CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 115 Fig. 5.39: Computer Output Microfilm Both Input and Output Devices The devices that can be used to perform both functions input and output are called Dual Devices. These devices are also called Dual Purpose Devices or Both Input/Output Devices. With the help of a dual purpose device, we can enter data into computer as well as we can output data from the computer to outside world. For example, Dual devices include: Touch Screen Monitor, Network Interface Card, Sound card handset etc. Touch Screen Monitor Touch Screen Monitor is an input/output device. It uses a special touch sensitive screen. The User can enter data by touching icons or menus on the screen. As soon as the user selects a command from menu, output is displayed on screen. Commonly touch screen monitors use sensors to detect touch of finger. Fig. 5.40: Touch Screen Monitor CU IDOL SELF LEARNING MATERIAL (SLM)

116 Computer Fundamentals Network Card Network cards allow computers to connect together to communicate with each other. Network cards have connections for cable, thin wire or wireless networks Cables connect internal components to the Motherboard, which is a board with series of electronic pathways and connections allowing the CPU to  communicate  with  the  other  components  of  the  computer. Fig. 5.41: Network Card Headsets A head-worn unit containing a microphone and one or two speakers. Employed in call centers and phone-intensive jobs, headsets allow people to easily have a phone conversation while using the computer. Wired headsets plug into the computer. Headset consists of speakers and microphone while speaker act output device and microphone act as input device. CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 117 Fig. 5.42: Headsets Sound Card A Sound Card is a card that translates signals into sounds that can be played back through speakers. The purpose of a sound card is to allow sound to be heard through the computer. It is not enough to let the computer transmit sound by itself, it either needs speakers or a microphone jack. The output signal is connected to an amplifier, headphones or external device that allows sound to be heard. The motherboard on most computer systems has an integrated sound card, which is often sufficient for many users. However, to get higher quality sound it can be upgraded to a separate sound card, which uses better and more expensive components. Alternatively, it is referred to as an audio output device, sound board or audio card. CU IDOL SELF LEARNING MATERIAL (SLM)

118 Computer Fundamentals Line in PCI Connectors Microphone Line Out (speaker) Gaming Controller Port Fig. 5.43: Sound Card Other Components of Computer While many important components have already been discussed, there are a great many important parts of the PC which do not fall under the previous headings. As brief summaries of those parts are as follows: Computer Cards A computer card is an expansion device that provides an existing computer with certain added capabilities. It is a printed circuit board that can be inserted into an expansion slot of a computer motherboard to add functionality to a computer system. Widely varying both in size, price, and purpose, these cards have the ability to make your computer perform functions or connect with external devices that it couldn't have previously. There are different types of card – Graphics cards, Sound cards, Network cards, TV tuner cards, Video processing expansion cards, serial port cards, multi-I/O cards, USB port cards and proprietary interface cards, memory expansion cards, etc. Some of them are given details in following: CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 119 Fig. 5.44: Computer Cards Graphics Card This circuit board is responsible from the visual outputs that will be displayed on the monitor. Nowadays, graphics cards have their own memory modules and processor chips, by which they lessen the load of CPU and RAM, hence enabling to see very detailed graphics and high quality animations and video. PCs are general-purpose devices that can be used in many areas of interest and of course there exists many other hardware components that can be added to them to increase their functionalities. These include CD-ROM drives, sound cards, radio cards, TV cards, modem cards, etc. Fig. 5.45: Graphics Card CU IDOL SELF LEARNING MATERIAL (SLM)

120 Computer Fundamentals Video Cards Video cards allow computers to display video and animation. Some video cards allow computers to display television as well as capture frames from video. A video card with a digital video camera allows computer users to produce live video. A high speed connection is required for effective video transmission. Fig. 5.46: Video Cards Color Cards Color cards allow computers to produce color (with a color monitor of course). The first color cards were 2 bit which produced 4 colors [CGA]. It was amazing what could be done with those 4 colors. Next came 4 bit allowing for 16 [EGA and VGA] colors. Then came 16 bit allowing for 1064 colors and then 24 bit which allows for almost 17 million colors and now 32 bit and higher allow monitors to display almost a billion separate colors. Fig. 5.47: Color Cards CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 121 Universal Serial Bus (USB) USB is pronounced as ‘yoo-es-bee’. This technology is now very widely used as the most popular connectivity interface standard, due to both its flexibility and simplicity for the end user. A Universal Serial Bus (USB) is a common interface that enables communication between devices and a host controller such as a personal computer (PC). It connects peripheral devices such as digital cameras, mice, keyboards, printers, scanners, media devices, external hard drives and flash drives. Fig. 5.48: Universal Serial Bus (USB) Computer Case A computer case (also known as a computer chassis, cabinet, box, tower, enclosure, housing or simply case) is the enclosure that contains the main components of a computer. A computer case is sometimes referred to metonymously as a CPU, referring to the primary component housed within the case; this was a more common term in the earlier days of home computers, when peripherals other than the motherboard were usually housed in their own separate cases. Cases are usually constructed from steel, aluminum or plastic. CU IDOL SELF LEARNING MATERIAL (SLM)

122 Computer Fundamentals Fig. 5.49: Computer Case Fan Many of the components that make up the modern personal computer are heat-critical, and malfunction if allowed to become too hot. With the amount of heat that is generated in certain areas, particularly by the CPU, it is therefore necessary to ensure that the inside of the unit has adequate ventilation. This is achieved mainly by the use of fans to draw cold air over the components in question. Heat sinks are also used to dissipate the heat over a larger area. Fig. 5.50: Fan CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 123 Modem The word “modem” is a contraction of the words modulator-demodulator. A modem is used to translate information transferred through telephone lines, cable or line-of-site wireless. Modems came into existence in the 1960s as a way to allow terminals to connect computers over the phone lines. Fig. 5.51: Modem The modem is a device that comprises both a modulator that changes a signal in some way in the forward direction and a demodulator that changes the signal back to its original form in the backward direction, essentially reversing the modulation process. Modems operate in balanced and symmetrical pairs, with one at each end of the communications circuit and with both having the same capabilities, at least at a minimum level. The amount of information that can travel through a line is limited. This limit is called bandwidth. Modems also use Error Correction which corrects transmission errors by constantly checking. Information is transferred in packets. Each packet is checked for errors and is resent if there is an error. Fig. 5.52: Broadband Modem CU IDOL SELF LEARNING MATERIAL (SLM)

124 Computer Fundamentals Modems are measured by the speed that the information is transferred. The measuring tool is called the baud rate. Originally modems worked at speeds below 2400 baud but today analog speeds of 56,000 are standard. Cable, wireless or digital subscriber lines can transfer information more fast with rates of 300,000 baud and up. Types of Modem (a) Internal Modem: Internal modems are more directly integrated into the computer system and, therefore, do not need any special attention. They are less costlier than other types of modem. (b) External Modem: They reside outside the computer and have their own power supply and connect with a cable to a computer’s serial port or USB port. The telephone line plugs into a socket on the rear panel of the modem. The advantage of this modem is its mobility, i.e., modem can be moved from one place (computer to another. (c) PC Card Modem: These modems, designed for portable computers, are the size of a credit card and fit into the PC Card slot on notebook and hand-held computers. These modems are removed when the modem is not needed. Except for their size, PC Card modems are like a combination of external and internal modems. These devices are plugged directly into a external slot in the portable computer, so no cable is required other than the telephone line connection. PC card modem also comes in wireless mode for wireless network. CCTV Closed Circuit Television (CCTV) is a system in which the circuit is closed and all the elements are directly connected. This is unlike broadcast television where any receiver that is correctly tuned can pick up the signal from the airwaves. Directly connected in this context includes systems linked by microwave, infrared beams, etc. The most common use of CCTV is in security camera systems. They’ve been found for years in areas like large retail shops, banks, and government institutions. To reduced costs in the manufacture of cameras and video recording equipment, camera systems are becoming more and more commonplace in smaller businesses and even private homes. CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 125 Fig. 5.53: CCTV Applications for CCTV CCTV is in security systems and such applications as retail shops, banks, government establishments, etc. The true scope for applications is almost unlimited. Few examples are listed below: 1. Monitoring traffic on a bridge. 2. Recording the inside of a baking oven to find the cause of problems. 3. Used by the stage manager of a show to see obscured parts of a set. 4. The well-publicised use at football stadiums. 5. Hidden in buses to control vandalism. 6. Recording the birth of a gorilla at a zoo. 7. Making a wildlife program using a large model helicopter. 8. Aerial photography from a hot air balloon. 9. Production control in a factory. 5.7 Software Requirements Software is a language of computer. Like a human language, there are many different languages. Computer software can be divided into three groups based on their use and application. These are – system software, application software and programming languages. CU IDOL SELF LEARNING MATERIAL (SLM)

126 Computer Fundamentals Generally, there are two types of Software – Application Software Software System Software 1. Operating Systems 2. Programming Languages 3. Language Translators 4. Utility Softwares Fig. 5.54: Types of Software The NAPCS, North American Product Classification System – Provisional Product List is classified software based on products and does not include services. The classification the software is divided to System Software and Application Software, with each having several sub levels: Software Publishing System Software Application Software Operating System Software General Business Productivity Network Software Home Use Applications Cross Industry Application Software Database Mgt. Software Vertical Market Application Software Utilities Software Development Tools and Other Application Software Programming Language Other System Software Fig. 5.55: Software Publishing (a) Application Software Application software, also known simply as application or application program is a tool that utilizes the capacities of a computer to support and improve the software user’s work. In other CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 127 word, it is a program or self-contained software that allows users to perform a specific task. A software development company employs various technologies like .net to provide .net application development services to its clients. (ib) System Software System software is the low-level software required to manage computer resources and support the production or execution of application programs. It helps run the computer hardware and system. Systems software includes the following: (i) Operating Systems (ii) Programming Languages (iii) Language Translators (iv) Utility/Service Softwares System software is a set of programs that control the operations of a computer and devices attached with the computer. It creates links between user and computer as well as controls the execution of application programs. System software are essential for a computer to do work, Without this software no link can be created between user and computer. (i) Operating Systems The operating system is a software program that acts as an interface between the users and the computer. This system is used as a base for creating and processing application software and to control and manage the hardware components such as keyboard, monitor, printer, scanner etc. Thus, it is a system which is used to control all activities of the computer. When user is working in a application software program, such as Microsoft Word the commands that user on give are willing the application are Sent through the operating system to the CPU. Windows 2000, Windows 95/ 98, Windows XP, Mac OS, UNIX and DOS are all examples of operating systems. (ii) Programming Languages The computer being an electronic machine, understands only the machine language which is nothing but a group of binary digits. It does not understand any of the languages that are used in our daily life. Thus, certain programming languages are developed to write instructions for the computer. CU IDOL SELF LEARNING MATERIAL (SLM)

128 Computer Fundamentals The operations of a computer are controlled by instructions. A user can select a sequence of computer operation and processes by entering instructions through the input device. Programming languages are flexible and free style but they follow very limited vocabularies and rigid rules of syntax and construction. The user has to learn computer programming languages to communicate with the computer. (iii) Language Translators Computers can understand the instructions only when they are written in their own language called the machine language. Therefore, a program written in any other language should be translated into machine language. Translator is a special program which accepts the user programs and check each statement and if it is grammatically correct, it produces a corresponding set of machine code instructions. There are three forms of translators: • Compilers • Interpreters • Assemblers (iv) Utility Programs Utility programs help to manage, maintain and control the computer resources. These programs help the computer run better and performs housekeeping tasks. These programs are available to help user with the day-to-day chore associated with personal computing and to keep you system running at peak performance. Utility programs include file management (creating, moving and renaming folders, copying and deleting files), file search, comparing file contents as well as performing diagnostic routines to check performance and current health of the hardware. Examples of utility programs include diagnostic programs, trace programs, input routines, and programs used to perform routine tasks, i.e., everyday tasks, such as copying data from one storage location to another. There are many different types of utility software and this list is hardly complete, but here are some of the main categories: CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 129 1. File Viewer 2. File Compression 3. Diagnostic Utility Programs 4. Un-Installer 5. Disk Scanner 6. Disk Defragmenter 7. Backup Utility 8. Virus Detection and Protection Programs 9. Peripheral Utilities and Drivers 10. Networking Utilities 5.8 Summary The hardware consists of the physical equipments which makes up the computer system like monitor, keyboard, CPU, hard disk, floppy drive, printer etc. normally all the items which can seen and touched are hardware items. Software is the computerized instructions that operate the computer, execute particular functions or tasks, and manipulate the data. Software is a language of computer. Like a human language, there are many different languages. Computer software can be divided into three groups based on their use and application. The computer being an electronic machine, understands only the machine language which is nothing but a group of binary digits. It does not understand any of the languages that are used in our daily life. Thus, certain programming languages are developed to write instructions for the computer. CU IDOL SELF LEARNING MATERIAL (SLM)

130 Computer Fundamentals Utility programs include file management (creating, moving and renaming folders, copying and deleting files), file search, comparing file contents as well as performing diagnostic routines to check performance and current health of the hardware. Mouse is a device that controls the movement of the cursor or pointer on a display screen. A mouse is a small object, it can roll along a hard, flat surface. Keyboard was the first input device to be used with computers and it is still the major and most widely used among all the input devices. It is the primary input device for entering text and numbers. It is an arrangement of keys on a board in an organized way - this is why it is called keyboard. A small, touch-sensitive pad is used as a pointing device on some portable computers. It is consisting of specialized surface that can translate the motion and position of a user’s fingers to relative position on screen. Output is anything that comes out of a computer. Output can be meaningful information or gibberish, and it can appear in a variety of forms – as binary numbers, as characters, as pictures, and as printed pages. 5.9 Key Words/Abbreviations  Software: Computer software, consisting of programs, codes or instructions.  Keyboard: A computer keyboard is a typewriter-style device.  Monitor: Monitor is a display screen used to provide visual output from a computer.  Hard Disk Drive (HDD): A hard disk drive (HDD), hard disk, hard drive or fixed disk is a data storage device that is used to store files  Floppy Disk Drive: A floppy disk drive (FDD), or floppy drive, is a hardware device that reads data storage information CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 131 5.10 Learning Activity 1. Discuss briefly about classification and the elements of the computer. —————————————————————————————————— —————————————————————————————————— 2. Explain various system software and application software. —————————————————————————————————— —————————————————————————————————— 5.11 Unit End Questions (MCQs and Descriptive) A. Descriptive Type Questions 1. Explain the relationship between Hardware and Software. 2. What is Application Software? 3. Explain Operating System. 4. What is Language Translators? B. Multiple Choice/Objective Type Questions 1. __________ runs on computer hardware and serves as platform for other software to run on. (a) Operating system (b) Application software (c) System software (d) All the above 2. Multiprogramming system __________. (a) Are easier to develop than single programming system (b) Execute each job faster CU IDOL SELF LEARNING MATERIAL (SLM)

132 Computer Fundamentals (c) Execute more jobs in the same time period (d) Are used only one large mainframe computers 3. __________ is the first program run on a computer when the computer boots up. (a) System software (b) Operating system (c) System operations (d) None of these 4. __________ shares characteristics with both hardware and software. (a) Operating system (b) Software (c) Data (d) None of these 5. Multiprogramming systems __________. (a) Are easier to develop than single programming systems (b) Execute each job faster (c) Execute more jobs in the same time period (d) Are used only one large mainframe computers 6. Which is the first program run on a computer when the computer boots up? (a) System software (b) Operating system (c) System operations (d) None of these 7. Which is built directly on the hardware? (a) Computer Environment (b) Application Software (c) Operating System (d) Database System Answers 1. (a), 2. (c), 3. (b), 4. (a), 5. (c), 6. (b), 7. (c) 5.12 References References of this unit have been given at the end of the book. CU IDOL SELF LEARNING MATERIAL (SLM)

Bringing Computer to Life 133 UNIT 6 BRINGING COMPUTER TO LIFE Structure: 6.0 Learning Objectives 6.2 Video Display 6.3 Storage Devices 6.4 Power Supplies 6.5 Summary 6.6 Key Words/Abbreviations 6.7 LearningActivity 6.8 Unit End Questions (MCQs and Descriptive) 6.9 References 6.0 Learning Objectives After studying this unit, you will be able to:  Understand the concept of Video Display  Discuss the Storage Devices of Computer  Understand the concept of Power Supplies CU IDOL SELF LEARNING MATERIAL (SLM)

134 Computer Fundamentals 6.1 Introduction A device that accepts video signals from a computer and provides information in a visual form. The display devices are known as output devices. The most commonly used output device in a graphics video monitor. The operations of most video monitors are based on the standard cathode- ray-tube design. A storage device is any computing hardware that is used for storing, porting and extracting data files and objects. It can hold and store information both temporarily and permanently, and can be internal or external to a computer, server or any similar computing device. A power supply is a component that supplies power to at least one electric load. Typically, it converts one type of electrical power to another, but it may also convert a different form of energy – such as solar, mechanical, or chemical - into electrical energy. 6.2 Video Display The display devices are known as output devices. The most commonly used output device in a graphics video monitor. The operations of most video monitors are based on the standard cathode- ray-tube design. How the Interactive Graphics Display Works? The modern graphics display is extremely simple in construction. It consists of three components: 1. A digital memory, or frame buffer, in which the displayed Image is stored as a matrix of intensity values. 2. A monitor 3. A display controller, which is a simple interface that passes the contents of the frame buffer to the monitor. Inside the frame buffer the image is stored as a pattern of binary digital numbers, which represent a rectangular array of picture elements, or pixel. The pixel is the smallest addressable screen element. In the Simplest case where we wish to store only black and white images, we can represent black pixels by 0's in the frame buffer and white Pixels by 1's. The display controller simply reads each successive byte of data from the frame buffer and converts each 0 and 1 to the corresponding video CU IDOL SELF LEARNING MATERIAL (SLM)

Bringing Computer to Life 135 signal. This signal is then fed to the monitor. If we wish to change the displayed picture all we need to do is to change of modify the frame buffer contents to represent the new pattern of pixels. Important Characteristics of Video Display Devices Persistence: The major difference between phosphors is their persistence. It decides how long they continue to emit light after the electron beam is removed. Persistence is defined as the time it takes the emitted light from the screen to decay to one-tenth of its original intensity. Lower persistence phosphors require higher refreshing rates to maintain a picture on the screen without flicker. However it is useful for displaying animations. On the other hand higher persistence phosphors are useful for displaying static and highly complex pictures. Resolution: Resolution indicates the maximum number of points that can be displayed without overlap on the CRT. It is defined as the number of points per centimeter that can be plotted horizontally and vertically. Resolution depends on the type of phosphor, the intensity to be displayed and the focusing and deflection systems used in the CRT. Aspect Ratio: It is the ratio of vertical points to horizontal points to produce equal length lines in both directions on the screen. An aspect ratio of 4/5 means that a vertical line plotted with four points has the same length as a horizontal line plotted with five points. 6.3 Storage Devices A storage device is a hardware device designed to store information. Computer data storage, often called ‘storage’ or’ ‘memory’, refers to computer components or devices that retain digital data used for computing for some interval of time. In contemporary usage, memory usually refers to a form of semiconductor storage known as random-access memory (RAM), which is fast but temporary storage. Storage today more commonly refers to mass storage — optical discs, forms of magnetic storage like hard disk drives, which is slower than RAM, but of a more permanent nature. Historically, memory and storage are respectively called ‘main memory’ or ‘primary storage’ or ‘internal memory’ and ‘secondary storage’ or ‘external memory’. CU IDOL SELF LEARNING MATERIAL (SLM)

136 Computer Fundamentals Types of Storage Device There are two types of storage devices used in computers – a ‘primary storage’ device and a ‘secondary storage’ device. Random Access Memory (RAM) Pronounced ram, acronym of Random Access Memory, a type of computer-memory that can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes. This is the memory that the computer uses while it is executing programs. RAM is the most common type of memory found in computers and other devices, such as printers. There are two basic types of RAM: • Dynamic RAM (DRAM) • Static RAM (SRAM) The two types differ in the technology they use to hold data, dynamic RAM being the more common type. Dynamic RAM needs to be refreshed thousands of time per second. Static RAM needs to be refreshed less often, which makes it faster but it is also more expensive than dynamic RAM. Both types of RAM are volatile, meaning that they lose their contents when the power is turned off. Fig. 6.1: Random Access Memory (RAM) In common usage, the term RAM is synonymous with main memory, the memory available to programs. For example, a computer with 8 MB RAM has approximately 8 million bytes of memory that programs can use. In contrast, ROM (Read-Only Memory refers to special memory used to store programs that boot the computer and perform refers to special memory used to store programs CU IDOL SELF LEARNING MATERIAL (SLM)

Bringing Computer to Life 137 that boot the computer and perform diagnostics. Most personal computers have a small amount of ROM (a few thousand bytes). In fact, both types of memory (ROM and RAM) allow random access. To be precise, therefore, RAM should be referred to as read/write RAM and ROM as read only RAM. Read Only Memory (ROM) Pronounced rom, acronym for Read-Only Memory, a computer memory on which has been prerecorded. The information stored on the ROM, chips is permanent and is stored when it is manufactured. Unlike the main memory (RAM), ROM retains its contents even when the computer is turned off. ROM is referred to as being nonvolatile whereas RAM is volatile. Fig. 6.2: Read-Only Memory (ROM) Most personal computers contain a small amount of ROM that stores critic programs such as the program that boots the computer. In addition, ROMs are used extensively in calculators and peripheral devices such as laser printers, whose fonts are often stored in ROMs. A variation of a ROM is the PROM (programmable read-only memory). PROMs are manufactured as blank chips on which data can be written. CU IDOL SELF LEARNING MATERIAL (SLM)

138 Computer Fundamentals PROM Pronounced prom, an acronym for programmable read-only memory. A PROM is a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever. Unlike the main memory, PROMs retain the contents when the computer is turned off. The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip you need a special device called a PROM programmer or a PROM burner. The process of programming a PROM is sometimes called burning the PROM. EPROM Acronym for Erasable Programmable Read-Only Memory and pronounced ee-prom. EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. EPROM differs from a PROM that is – a PROM can be written to only once and cannot be erased. EPROMs are used widely in PCs because they enable the manufacturer to change the contents of the PROM before the computer is actually skipped. This means bugs can be removed and new versions installed shortly before delivery. EEPROM Acronym for electrically Erasable Programmable Read-only Memory. Pronounced double ee- prom. An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like all other types of ROM, EEPROM is not as fast as RAM. Flash Memory Flash memory is a special type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCs have their BIOS (Basic Input/Output System) stored on a flash memory chip so that it can easily be updated necessary. Such a BIOS is sometimes called a flash BIOS. Flash memory is also popular in modems because it enables the modem manufacturer to support new protocols as they become standardized. CU IDOL SELF LEARNING MATERIAL (SLM)

Bringing Computer to Life 139 The principal difference between EEPROM and flash memory is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks. This makes flash memory faster. Cache Memory The cache memory is very important to the PC system and its speed. It is a special and very high speed memory, which is used to increase the speed of processing by making current program and data available to the CPU at a rapid rate. Auxiliary Storage Main Memory CPU Cache Memory Fig. 6.3: Cache Memory Cache memory is volatile, i.e., when the computer is shut down, the data stored there is lost. Today, the cache memory runs 5 times faster than the motherboard. The CPU looks in the cache for the data it needs. If the data is there, it will retrieve it and process it. If the data is not there, then the CPU accesses the system memory and then puts a copy of the new data in the cache before processing it. Cache memory is placed at two levels. They are called first-level cache (L1) and second-level cache (L2). The cache memory is placed in between CPU and main memory. Cache sits on newer processor as L1 (level 1) memory and on the board as L2 memory. This allows kind of a buffer for the CPU. CPU is faster than the rest of the system in most cases and needs a place to set information that can be accessed fast, this is where L1 and L2 come in. The L1 cache is a little more hush. This cache site on the CPU allows a buffer for the rest of the system to keep up with it. The same goes with L2 cache but act more for information heading out of the CPU rather than in it. CU IDOL SELF LEARNING MATERIAL (SLM)

140 Computer Fundamentals Virtual Memory Memory is hardware that your computer uses to load the operating system and run programs. Because computer has a finite amount of RAM, it is possible to run out of memory when too many programs are running at one time. This is where virtual memory comes in. Virtual memory increases the available memory of computer by enlarging the “address space,” or places in memory where data can be stored. It does this by using hard disk space for additional memory allocation. CACHE VIRTUAL CPU MEMORY RAM MEMORY HARD DISK Fig. 6.4: Virtual Memory The area of the hard disk that stores the RAM image is called a page file, which extension in windows machine is .SWP. It holds pages of RAM on the hard disk, and the operating system moves data back and forth between the page file and RAM. When the operating system has to constantly swap information back and forth between RAM and the hard disk, this is called thrashing, which can make the computer incredibly slow. This means that the more virtual memory is used, the more it will slow the computer down. While virtual memory enables the computer to run more programs than it could otherwise, it is best to have as much physical memory as possible. This allows the computer to run most programs directly from the RAM, avoiding the need to use virtual memory. Having more RAM means computer works less, making it a faster, happier machine. The space on a HDD that is used to store the overflow from memory is called swap space. The swap space is divided into segments called pages, each of which is associated with a specific address in memory. When an address is referenced, the page is swapped into memory. It is returned to the disk when no longer needed and other pages are called. This management of virtual memory is performed by a type of hardware circuitry called a Memory Management Unit (MMU). Secondary Storage Device A storage medium that holds information until it is deleted or overwritten. The memory capacity of the computer can be increased by using secondary or external or auxiliary memory units to the CU IDOL SELF LEARNING MATERIAL (SLM)

Bringing Computer to Life 141 computer. This is the additional memory used to supplement the storage capability. It is less expensive and more flexible than main memory. These devices store information such as software and data permanently. For example, magnetic disk, magnetic tapes etc. Magnetic Tape They are convenient, inexpensive devices which can be used to store large volumes of data. The magnetic tape is similar to the commonly used audio tape recorders. The tape is wound on a spool and threaded manually on the take-up spool. Data on tapes is stored as blocks, therefore recording and retrieving is sequential. The access time in the case of magnetic tapes is quite high. The various types of magnetic tapes are as follows: Reel to Reel Tapes Large computers use tape devices to store and read data on reels of tape. A reel of magnetic tape is half inch in width and can store 1,600 to 6,000 characters per inch along its 2,400 feet length. Fig. 6.5: Reel to Reel Tapes Cassette and Cartridge Tapes Tape drives attached to early personal computers used cassette tapes similar to the familiar audio cassettes. Cassettes and reels are now being replaced by cartridge tapes. These cartridges are self contained in hard plastic cells that are easy to mount in a tape drive and store when not in use. They can hold data 40 MB to 10 GB. Magnetic Disks A magnetic disk is a circular platter that is made of smooth metal or mylar plastic. It is coated with magnetic material. CU IDOL SELF LEARNING MATERIAL (SLM)

142 Computer Fundamentals Fig. 6.6: Magnetic Disks Data is stored or retrieved from the disk using a conducting coil called the head. During read/ write the head is stationary while the platter rotates beneath it. With disks it is possible to directly access records by specifying the address or location. That is why disks are called direct access storage devices. The various types of magnetic disks include: Floppy Disk Floppy disk is a soft magnetic disk. It is called floppy because it flops if you wave it. Unlike most hard disks, floppy disks (often called floppies or diskettes) are portable, because you can remove them from a disk drive. Disk drives for floppy disks are called floppy drives. Floppy disks are slower to access than hard disks and have less storage capacity, but they are less expensive and portable. Fig. 6.7: Floppy Disk CU IDOL SELF LEARNING MATERIAL (SLM)