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  1. HARDWARE UNITS Compiled by : S. Agarwal, Lecturer & Systems Incharge St. Xavier’s Computer Centre, St. Xavier’s College Kolkata. March-2003

  2. ANATOMY OF THE COMPUTER BASIC STRUCTURE The computer receives input, processes it and delivers output. To perform these tasks it has different units and each unit is responsible for a specific task. The units are INPUT, MEMORY, CONTROL UNIT (CU), ARITHMETIC & LOGIC UNIT (ALU) AND OUTPUT. The CU and ALU together are called CENTRAL PROCESSING UNIT (CPU).

  3. INPUT DEVICE It is used for transferring data from the users’ end to the computer. OUTPUT DEVICE It is used to transfer processed information from the computer to the user in a way required by the user.

  4. MEMORY UNIT It stores instruction and data and provides them to the various other units as and when required. It is basically the working memory of the computer system. This memory unit is volatile, i.e. it is temporary memory and nothing can be stored here permanently. The information is stored in the main memory as long the computer is switched on or as long as it is required by the computer.

  5. CONTROL UNIT Controls the various operations within a computer. It basically manages all the other units and devices of the computer system. It does so by transmitting timing and control signals to the various devices and units.

  6. ARITHMETIC & LOGIC UNIT It performs the various arithmetic and logical operations on the data stored in memory, as dictated by the instruction. There are various basic circuits to perform these operations.

  7. SECONDARY STORAGE It stores the various data, information and programs permanently for future retrieval. The information is organised in such a way to retrieve it in minimum time whenever required. The stored information remains as long the user wants it.

  8. BUS These are a set of connecting wires used for setting interconnection between the various devices in the system. Each set of bus has a specific function to perform like carrying data, carrying control signals and addresses.


  10. KEYBOARD A keyboard on a computer is almost identical to a keyboard on a typewriter. Computer keyboards will typically have extra keys, however. Some of these keys (common examples include Control, Alt, and Meta) are meant to be used in conjunction with other keys just like shift on a regular typewriter. Other keys (common examples include Insert, Delete, Home, End, Help, function keys,etc.) are meant to be used independently and often perform editing tasks. Keyboards on different platforms will often look slightly different and have somewhat different collections of keys. Some keyboards even have independent shift lock and caps lock keys. Smaller keyboards with only math-related keys are typically called "keypads".

  11. Although the typing portion of the computer keyboard is identical to a standard typewriter, computers have several additional keys that perform different functions.

  12. Pointing Device A pointing device is any hardware component that allows a user to input spatial data to a computer. CAD systems and Graphical User Interfaces (GUI) allow the user to control and provide data to the computer using physical "gestures" - point, click, and drag - typically by moving a hand-held mouse across the surface of the physical desktop and activating switches on the mouse. Movements of the pointing device are echoed on the screen by movements of the mouse pointer and other visual changes. While the most common pointing device by far is the mouse, other kinds include trackball, touchpad, pointing stick, lightpen, various kinds of digitizing tablets which use a stylus, and even a special "data glove" that translates the user's movements to computer gestures.

  13. MOUSE A mouse is a small device that a computer user pushes across a desk surface in order to point to a place on a display screen and to select one or more actions to take from that position. It is a handheld pointing device for computers, involving a small object fitted with one or more buttons and shaped to sit naturally under the hand. The underside of the mouse houses a device that detects the mouse's motion relative to the flat surface on which it sits. The mouse's 2D motion is typically translated into the motion of a cursor on the display.

  14. Common mouse actions include: • clicking the mouse button to select an object or to place the cursor at a certain point within a document; • double-clicking the mouse button to start a program or open a folder; and • dragging (holding down) the mouse button and moving the mouse to highlight a menu command or a selected bit of text.

  15. Touch pad A touch pad is a device for pointing (controlling input positioning) on a computer display screen. It is an alternative to the mouse. Originally incorporated in laptop computers, touch pads are also being made for use with desktop computers. A touch pad works by sensing the user's finger movement and downward pressure.

  16. Graphics Tablet A graphics tablet (or digitizing tablet) is a computer peripheral device that allows for a relatively simple method of inputing hand-drawn graphics or art into a computer in real time. They typically consist of a large flat surface for drawing on, and an attached "stylus" for drawing on the surface, originally as a part of the electronics, but later simply to provide an accurate but smooth "point". This device also allows the computer user to control the mouse cursor by tracking the stylus pen across the tablet. To most users, the cordless, stylus pen is much easier and faster to use than a mouse and has less strain on your hand.

  17. TRACKBALL A trackball is a computer cursor control device used in many notebook and laptop computers. The trackball is usually located in front of the keyboard toward the user. Essentially, the trackball is an upside-down mouse that rotates in place within a socket. The user rolls the ball to direct the cursor to the desired place on the screen and can click one of two buttons (identical to mouse buttons) near the trackball to select desktop objects or position the cursor for text entry.

  18. TOUCHSCREEN A touchscreen is an input device that allows users to operate a PC by simply touching the display screen. Touch input is suitable for a wide variety of computing applications. A touchscreen can be used with most PC systems as easily as other input devices such as track balls or touch pads. Browse the links below to learn more about touch input technology and how it can work for you. Touchscreen systems are being used in a variety of applications, including point-of-sale systems, public information displays, industrial control systems, and more. Follow this link for additional examples of how touch technology is being used today.

  19. Light pen Alightpen is a device similar to a touch screen, but is facilitated by use of a special light sensitive pen instead of the finger. The advantage of using a pen is more accurate screen input other that of a touch screen.

  20. JOYSTICK A lever that moves in all directions and controls the movement of a pointer or some other display symbol. A joystick is similar to a mouse, except that with a mouse the cursor stops moving as soon as you stop moving the mouse. 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.

  21. SCANNER Scanner is an image acquisition device connected to the computer, which captures either an image of a text document or a picture and transfers it into bits of information, which a computer can understand and manipulate. Scanning an image is like a copier copying an image. The major difference is that the output of scanning is an electronic file which can be edited by a software and stored in a disk.

  22. DIGITAL CAMERA A digital camera records and stores photographic images in digital form that can be fed to a computer as the impressions are recorded or stored in the camera for later loading into a computer or printer. The big advantage of digital cameras is that making photos is both inexpensive and fast because there is no film processing.

  23. A digital camera stores images digitally rather than recording them on film. Once a picture has been taken, it can be downloaded to a computer system, and then manipulated with a graphics program and printed. Unlike film photographs, which have an almost infinite resolution, digital photos are limited by the amount of memory in the camera, the optical resolution of the digitizing mechanism, and, finally, by the resolution of the final output device. Even the best digital cameras connected to the best printers cannot produce film-quality photos. However, if the final output device is a laser printer, it doesn't really matter whether you take a real photo and then scan it, or take a digital photo. In both cases, the image must eventually be reduced to the resolution of the printer.

  24. Various input techniques

  25. MICR MICR, an acronym that stands for Magnetic Ink Character Recognition, is the special set of characters and symbols that appear at the bottom of checks and other financial documents. MICR technology was developed in the mid-1950s to more efficiently process checks which were increasing in volume and quickly overwhelming the manual processing system. Today, many types of financial documents utilize MICR technology, not only traditional bank deposit slips and loan payment stubs, but also gift certificates and stock certificates have adopted this standard. However, checks still account for the largest volume of MICR documents.

  26. MICR characters are either printed in special inks using offset printing presses or printed with MICR toners using a laser printer. The MICR font characters are magnetized and read electronically by special reader/sorter equipment by financial institutions. The MICR line contains critical account information and instructions on how the payment is to be automatically routed and processed. Processing is done initially at the bank of deposit and progresses through the Federal Reserve System in the U.S. and/or other banking systems

  27. OCR Next to keypunching, Optical Character Recognition is the oldest data entry technique in existence. Long before the first key-to-disk system of CRT was used, Optical Character Readers were entering data in commercial and government EDP installations. Data Entry through OCR is faster, more accurate, and generally more efficient than keystroke data entry. Desktop OCR scanners can read typewritten data into a computer at rates up to 2400 words per minute!

  28. Reasons for Using OCR • There are a number of reasons for choosing OCR scanning over other methods of data entry. Some of the more significant include: • To reduce Data Entry Errors • To Consolidate Data Entry • To Handle Peak Loads • Human Readable • Can Be Used with Many Printing Techniques • Scanning Corrections

  29. Bar Code Bar code, composed of bars and spaces of varying width, provides a means of expression for human-readable characters in a form (bars and spaces) readable by machines. And in order to read the bar code, there are a wide variety of readers available, each designed for a specific purpose. The advantages are that the bar code provides timely, error free information that can be used to validate receipt, movement or counting of products. It reduces key entry time, transcribing time and almost all errors.

  30. Black and white stripes, such as those shown below, are often seen on packages of snacks, foodstuff, and sundries stacked on supermarket shelves or convenience stores - these are known as "Bar Code". The bar code can also be found on industrial products, or on delivery request forms for home and office deliveries - their uses are wide ranging.

  31. OMR OMR (Optical Mark Reading) is the process to detect the presence of intended marked responses. A mark or response position as it is often called, registers significantly less light than the surrounding paper. In order to be detected by the a mark has to: Be positioned correctly on the paper Be significantly darker than the surrounding paper OMR ususally refer to a technique that uses special hardware equiped with light sensors that capture the reflection or absence of reflection on paper.

  32. Advantages of OMR readers : • OMR has a better recognition rate because fewer mistakes are made by machines to read marks than by reading handwritten characters. • Large volumes of data can be collected quickly and easily without the need for specially trained staff. • The cost of inputting data and the chance of data input errors can be reduced because it is not necessary to type the details for data entry. • Disadvantages of OMR readers: • Documents for optical mark recognition are complicated to design. • The OMR reader needs to be reprogrammed for each new document design. • OMR readers are relatively slow. • The person putting marks on the documents must follow the instructions precisely. • Any folding or dirt on a form may prevent the form from being read correctly.

  33. Input Device Description Usage Keyboard Data can be entered by pressing the corresponding keys on the keyboard. Text input Mouse/ Trackball It uses the movement of a small ball to control the pointer and uses buttons to perform activities. Moving the pointer, selecting options and graphics input Touch pad It uses the movement of a finger to control the pointer and uses buttons to perform activities. Moving the pointer, selecting options and graphics input Joystick It uses the movement of a vertical stem to control the pointer and uses buttons to perform actions. Playing video games

  34. Input Device Description Usage Touch screen Data can be entered by touching the screen. Information seeking Digitizer It converts points, lines and curves from a drawing or a photograph into digital signals. Graphics input Graphic tablet It allows a user to input graphic designs into a computer. Graphics input Bar code reader It identifies a bar code by the reflected light pattern from the bar code lines. Reading bar codes

  35. Input Device Description Usage Optical character reader It recognizes characters with special typefaces. Reading retail prices, text input Image scanner It captures images or text into the computer. Graphics input Magnetic card reader It reads data stored in the magnetic strip on a magnetic card. Reading magnetic cards

  36. Input Device Description Usage Smart card reader It reads data stored in the chip on a smart card. Reading smart cards Speech recognition device Data or commands can be inputted to the computer with spoken words. Security purposes, handicapped people Digital camera It records images in the form of digital data. Image input Digital video camera It allows a user to input video images into the computer in digital form. Video image input

  37. Output devices used to produce information to users in the form of hardcopies (printed output) or screen display.

  38. VDU or MONITOR A monitor, also called the Visual Display Unit (VDU) or a display screen, is the physical unit where the CRT, or other image-projection means and other related parts are placed. It is a separate unit connected to the computer via cables. One distinguishable part of a monitor, the screen, is a glass surface on which images produced by the computer’s video adapter are displayed. The size of a screen is measured from one corner to the diagonally opposite corner. Common screen sizes are 14, 17, 19 and 21 inches. Monitors can be classified by color capability into monochrome (two-color display), gray-scale (displays different shades of gray), and colored (many-color display, RGB monitor). Together with the development on the color capabilities of monitors, are the improvements on the display modes (sometimes called video or graphics standards).

  39. The technology behind monitors and televisions is The cathode-ray tube, or CRT, A CRT is an sealed glass bottle with no air inside. It begins with a slim neck and tapers outward until it forms a large base. The base is the monitor’s ‘screen’ and is coated on the inside with a matrix of thousands of tiny phosphor dots. Phosphors are chemicals which emit light when excited by a stream of electrons: different phosphors emit different coloured light. Each dot consists of three blobs of coloured phosphor: one red, one green, one blue. These groups of three phosphors make up what is known as a single pixel

  40. Display modes Originally, a PC could only display text, and in monochrome only. There are now a variety of display modes, but display quality still depends on the PC’s video card or adapter. For the full benefit of higher resolution and more colors, the following display modes have been developed over the years. CGA : Color Graphics Adapter (CGA) was introduced by IBM in 1981. It was capable of providing four colors and displaying images at a maximum resolution of 320x200 pixels. EGA : EGA (Extended Graphics Adapter) was introduced in 1984. It provides up to 16 colors and an improved resolution of 640x350 pixels. EGA made text-reading easier than CGA, but it is still did not provide enough resolution for sophisticated graphics designs or desktop publishing.

  41. VGA : Introduced in 1987, Video Graphics Array(VGA) provides a 640x480 resolution at 16 colors, or a 320 X 200 resolution at 256 colors. VGA has become the accepted standard for the usually less expensive IBM PC-compatibles or clone computers. SVGA : Super VGA provides greater resolution than VGA. Typically, it can support a palette of up to 16,000,000 colors. The number of colors that can be displayed at the same time in a certain computer, however, may be limited by the amount of its video memory. Most PCs now support the SVGA display. Depending on its size, an SVGA monitor can provide one of the following resolutions: 800x600 pixels 1024x768 pixels 1280x1024 pixels 1600x1200 pixels XGA : Extended Graphics Display (XGA) was introduced in 1990. The newer version of XGA offers a good resolution of 800x600 pixels in 16,000,000 colors (true color) and 1024x768 pixels in 65,536 colors.

  42. Printer In computers, a printer is a device that accepts text and graphic output from a computer and transfers the information to paper, usually to standard size sheets of paper. Printers are sometimes sold with computers, but more frequently are purchased separately. Printers vary in size, speed, sophistication, and cost. In general, more expensive printers are used for higher-resolution color printing.

  43. Personal computer printers can be distinguished as impact or non-impact printers. Early impact printers worked something like an automatic typewriter, with a key striking an inked impression on paper for each printed character. The dot-matrix printer was a popular low-cost personal computer printer. It's an impact printer that strikes the paper a line at a time. The best-known non-impact printers are the inkjet printer, of which several makes of low-cost color printers are an example, and the laser printer. The inkjet sprays ink from an ink cartridge at very close range to the paper as it rolls by. The laser printer uses a laser beam reflected from a mirror to attract ink (called toner) to selected paper areas as a sheet rolls over a drum.

  44. Dot Matrix printer : A Dot Matrix printer is an impact printer that forms characters as a series of dots. The print head contains a grid of pins which form a character. This heads stamps on to the paper through an inked ribbon to produce a character (for example, "H") that is made up of dots. The print heads can have from 9 to 24 pins in them. The more pins the print head has, the better the quality of the printed output. Printers with 24 pins produce letter quality output. The quality of the printed output is measured in dpi (dots per inch). The higher the dpi, the better the quality of the printed output.

  45. Ink-Jet printer : • An inkjet printer is any printer that places extremely small droplets of ink onto paper to create an image. If you ever look at a piece of paper that has come out of an inkjet printer, you know that: • The dots are extremely small (usually between 50 and 60 microns in diameter), so small that they are tinier than the diameter of a human hair (70 microns)! • The dots are positioned very precisely, with resolutions of up to 1440x720 dots per inch (dpi). • The dots can have different colors combined together to create photo-quality images.

  46. Laser Printer : A Laser printer uses a laser beam to print. The laser creates an image on a drum inside the printer. This picks up toner and prints the image on to the paper like a photocopier does. The main advantages of laser printers are speed, precision and economy. A laser can move very quickly, so it can "write" with much greater speed than an ink jet. And because the laser beam has an unvarying diameter, it can draw more precisely, without spilling any excess ink.

  47. The four printer qualities of most interest to most users are: Color: Color is important for users who need to print pages for presentations or maps and other pages where color is part of the information. Color printers can also be set to print only in black-and-white. Color printers are more expensive to operate since they use two ink cartridges (one color and one black ink) that need to be replaced after a certain number of pages. Users who don't have a specific need for color and who print a lot of pages will find a black-and-white printer cheaper to operate. Resolution: Printer resolution (the sharpness of text and images on paper) is usually measured in dots per inch (dpi). Most inexpensive printers provide sufficient resolution for most purposes at 600 dpi. Speed: If you do much printing, the speed of the printer becomes important. Inexpensive printers print only about 3 to 6 sheets per minute. Color printing is slower. More expensive printers are much faster. Memory: Most printers come with a small amount of memory (for example, one megabyte) that can be expanded by the user. Having more than the minimum amount of memory is helpful and faster when printing out pages with large images or tables with lines around them (which the printer treats as a large image). Large volume of information are printed with the help of a print spooler which uses the printer memory efficiently to complete the print job.

  48. PlotterA plotter is a printer that interprets commands from a computer to make line drawings on paper with one or more automated pens. Unlike a regular printer, the plotter can draw continuous point-to-point lines directly from vector graphics files or commands. There are a number of different types of plotters: a drum plotter draws on paper wrapped around a drum which turns to produce one direction of the plot, while the pens move to provide the other direction; a flatbed plotter draws on paper placed on a flat surface; and an electrostatic plotter draws on negatively charged paper with positively charged toner.

  49. Comparisons between different output devices: Output Device Description Usage Visual display unit It displays images on screen. Image output Dot-matrix printer It is a noisy, low speed and quality printer. Printing multiple hardcopies in one strike Inkjet printer It is a quiet, quite high speed and quality printer. Printing documents, graphics Laser printer It is quiet, high speed and best quality printer. Printing high quality documents and graphics Plotter It produces high quality line drawings. Producing maps, charts, building plans and circuit diagrams. Sound/speech synthesizing devices It converts information into speech. Automatic telephone answering systems, voice dictionaries