Bis Chapter3

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Bis Chapter3

  1. 1. Chapter 3 Hardware
  2. 2. Components of a computer system <ul><li>A computer system consists of a number of interrelated components including hardware and software that work together with the aim of converting data into information. </li></ul><ul><li>In a computer system, processing is carried out electronically, usually with little or no intervention from a human user. </li></ul><ul><li>The components of a computer system include hardware and software. </li></ul>
  3. 3. Figure 3.1 Basic hardware components of a computer system
  4. 4. Computer hardware <ul><li>Computer hardware describes the physical components of a computer system. </li></ul><ul><li>The hardware of a computer system consist s of: </li></ul><ul><ul><li>Input devices </li></ul></ul><ul><ul><li>Memory </li></ul></ul><ul><ul><li>Central Processing Unit (CPU) </li></ul></ul><ul><ul><li>Output devices </li></ul></ul><ul><ul><li>Storage devices </li></ul></ul>
  5. 5. Hardware components <ul><li>Input device – Mouse, Keyboard, Touch screen, another system </li></ul><ul><li>Processor – a PC’s chip manufactured by Intel or AMD </li></ul><ul><li>Output device – screen, printer </li></ul><ul><li>Primary storage – Random Access Memory (RAM) </li></ul><ul><li>Secondary storage – magnetic (disk drives) and optical storage (CD-ROM and DVD) </li></ul>
  6. 6. Input devices <ul><li>Input device are used to capture or enter data into the computer. </li></ul><ul><li>Such data (in human-sensible form) needs to be converted into a format that supports processing by computer. </li></ul><ul><li>Input devices convert data into a form that makes them machine-sensible . </li></ul>
  7. 7. Central processing unit (CPU) <ul><li>CPU is the processor found in a computer system that controls all of the computer’s main functions and enables users to execute programs or process data. </li></ul><ul><li>CPU performs processing by carrying out instructions given in the form of computer programs. </li></ul>
  8. 8. Memory <ul><li>Memory (or primary storage) is used as a temporary means of storage data and instructions. </li></ul><ul><li>Memory is used to store: </li></ul><ul><ul><li>Data awaiting processing </li></ul></ul><ul><ul><li>Instructions loaded from software which are used to process data or control the computer system </li></ul></ul><ul><ul><li>Data or information that has been processed </li></ul></ul>
  9. 9. Storage devices <ul><li>Storages devices provide a means of storing data and programs permanently until they are required. </li></ul><ul><li>As an example, a program is stored on a hard disk drive until it is needed. </li></ul><ul><li>When the program is activated, it is transferred from the storage device into the computer’s memory. </li></ul><ul><li>When the program has ended or is no longer needed, it can be removed from memory so that other programs or data can be used. </li></ul>
  10. 10. Output devices <ul><li>Output devices translate the results of processing –output into a a human-readable form. </li></ul>
  11. 11. Figure 3.2 A personal computer labeled with the typical components
  12. 12. Major categories of computers <ul><li>A traditional view of computer technology suggests three basic categories of computer: mainframe, minicomputer and micro-computer . </li></ul><ul><li>The physical forms of these different types of system and some newer types of computers are illustrated in Figure 3.3 </li></ul>
  13. 13. Figure 3.3 Different forms of computer system
  14. 14. Mainframe computers <ul><li>Mainframes are powerful computers used for large-scale data processing </li></ul><ul><li>A traditional view of mainframe computers saw them as large, extremely powerful machines designed for large-scale data-processing activities. </li></ul><ul><li>Examples are those from IBM, Tandem, Amdahl and Hitachi. </li></ul><ul><li>The use of mainframe computers has declined steadily over the past two decades. </li></ul>
  15. 15. Legacy systems <ul><li>In many organizations, mainframe computers are considered legacy systems . </li></ul><ul><li>Legacy system is a system which has been superseded by new technologies or business practices. </li></ul><ul><li>Managers recognize that the existing system may not be entirely adequate to meet the company’s needs, a changeover would be difficult – or even impossible – to implement. </li></ul><ul><li>This can be for a number of different reasons: </li></ul>
  16. 16. Reasons of retaining mainframe computers <ul><li>A lot of investment has been used in developing and maintaining the mainframe system that a move towards more modern technology would be prohibited by the costs involved. </li></ul><ul><li>The data and information produced by the mainframe system are critical to the company’s operations </li></ul><ul><li>The links between the existing mainframe system and the company’s major business activities are so strong that it is not possible to introduce new systems a little at a time. </li></ul>
  17. 17. Minicomputers and servers <ul><li>The minicomputer combines some of the characteristics of the mainframe computer and the microcomputer. </li></ul><ul><li>Today, they are often referred to as servers by companies such as SUN and Hewlett-Packard. </li></ul><ul><li>Different types of server may have different functions, such as managing a network or hosting a database. </li></ul>
  18. 18. Microcomputers <ul><li>Microcomputers are considered less powerful than minicomputers and mainframes, but are more flexible and relatively inexpensive to purchase. </li></ul><ul><li>Microcomputers are now often referred to as the “client” machine which receives services and data form a “server” machine forming the client/server architecture which is a common type of communications structure. </li></ul><ul><li>The client/server architecture consists of client computers such as PCs sharing resources such as a database stored on a more powerful server computers. </li></ul>
  19. 19. Types of microcomputers <ul><li>In industry, several types of microcomputer are in common use. </li></ul><ul><li>The IBM-compatible or personal computer (PC) is considered the standard for general business use. </li></ul><ul><li>The Apple Macintosh or iMac is often used for professional desktop publishing applications, such as the production of newspapers. </li></ul><ul><li>Workstations , such as those produced by SUN, are typically used in the area of computer graphics. Typical applications include computer aided design (CAD) and animation. </li></ul>
  20. 20. Types of microcomputers <ul><li>Desktop computer is intended for office use and supports the day-to-day activities of an organization’s employees. </li></ul><ul><li>These machines tend to be placed in a fixed location and connected permanently to items such as printers, scanners and other devices. </li></ul><ul><li>Desktop computer is the most common type of microcomputer. </li></ul>
  21. 21. Types of microcomputers <ul><li>The p ortable computer is largely self-contained, featuring its own power supply, keyboard, pointing device and visual display unit. </li></ul><ul><li>Modern portables tend to weigh very little and fit easily into a briefcase. </li></ul><ul><li>Portable computers are often described as notebooks . </li></ul><ul><li>A notebook or laptop is approximately the size of an A4 writing pad. </li></ul>
  22. 22. Organiser/PDA <ul><li>A personal digital assistant (PDA) can be thought of as a sophisticated personal organizer. </li></ul><ul><li>A PDA is normally a hand-held device, often no larger than a pocket calculator. </li></ul><ul><li>The typical functions of a PDA can include: </li></ul><ul><ul><li>Address book </li></ul></ul><ul><ul><li>Appointment scheduler </li></ul></ul><ul><ul><li>Calculator </li></ul></ul><ul><ul><li>Expenses tracking </li></ul></ul><ul><ul><li>Currency conversion </li></ul></ul><ul><ul><li>Alarm clock </li></ul></ul><ul><ul><li>World time display </li></ul></ul><ul><ul><li>Other features that allow users to store notes such as to-do lists. </li></ul></ul>
  23. 23. Organiser/PDA (Continued) <ul><li>More sophisticated models such as Palm Pilot or Pocket PC include a more powerful range of tools, including communications, spreadsheet and word processing applications. </li></ul>
  24. 24. Connectivity <ul><li>Modern computers, PDAs, mobile phones and other devices are often equipped with a wireless adaptor of some kind. </li></ul><ul><li>One of the most common standards used by wireless devices is called Bluetooth . </li></ul><ul><li>Bluetooth is popular because it is inexpensive to integrate into products and is almost completely automatic. </li></ul><ul><li>A Bluetooth adaptor will locate any compatible devices that are nearby and initiate a connection automatically. </li></ul><ul><li>Another technology used for wireless connections is called Firewire . </li></ul><ul><li>Firewire is often used by computer peripherals that require very high data transfer speeds, such as digital video equipment and external hard disks. </li></ul>
  25. 25. Network computer <ul><li>Network computer (NC) is a computer providing access to a network system, which to reduce cost features limited disk storage, a less powerful processor and less memory. </li></ul><ul><li>Network computer is used to provide access to a network system, such as an intranet or the Internet, at minimal cost. </li></ul><ul><li>The network computer is able to call upon the resources of the network server, only limited processing power is required. </li></ul>
  26. 26. Network computer <ul><li>Simple tasks can be carried out by the network computer itself. </li></ul><ul><li>More complex tasks, such as those that make intensive use of a computer’s processor, are dealt with by the network server and the results are passed back to the network computer. </li></ul><ul><li>Also, since software applications and data can be accessed via the network, only minimal storage capacity is required. </li></ul><ul><li>This type of architecture is called thin client. </li></ul>
  27. 27. Network computer <ul><li>Network computers are popular with cost-conscious IS managers since they potentially reduce the total cost of ownership (TCO) associated with computer systems. </li></ul><ul><li>The TCO describes a range of different expenses incurred by purchasing and maintaining a computer system. </li></ul><ul><li>Such costs include the original cost of the hardware and software, upgrades, maintenance, technical support and training. </li></ul>
  28. 28. Network computer <ul><li>Network computers act to reduce the cost of ownership in several ways: </li></ul><ul><li>The initial purchase costs of hardware and software are low. </li></ul><ul><li>Since network computers can be managed via a central network server, administration costs can be reduced. Network computers are often described as offering the potential to achieve zero administration, a point where the centralized management and control of the computers attached to a network server makes administration costs potentially negligible. </li></ul>
  29. 29. Network computer <ul><li>Since the network computers contains fewer components than a conventional personal computer, it is less expensive to maintain, repair and replace. </li></ul><ul><li>As network computers are often used for a relatively small number of applications, training and support costs can be reduced. </li></ul>
  30. 30. TOPICS <ul><li>Components of a computer system </li></ul><ul><li>Major categories of computers </li></ul><ul><li>Types of microcomputers </li></ul><ul><li>Input devices </li></ul><ul><li>Selecting input devices </li></ul><ul><li>Output devices </li></ul><ul><li>Selecting output devices </li></ul><ul><li>Storage devices </li></ul><ul><li>Selecting storage devices </li></ul><ul><li>Processors </li></ul><ul><li>Other components of a personal computer </li></ul><ul><li>Selecting hardware suppliers </li></ul>
  31. 31. Input devices <ul><li>Input devices are used to enter data or instructions. </li></ul><ul><li>The choice of an input device often depend upon the quantity of data to be entered. </li></ul><ul><li>Data input can be carried out by human operators using input devices such as mouse or keyboard. </li></ul><ul><li>Large-scale data input may require a direct capture device to acquire and store data automatically. </li></ul><ul><li>There are several different methods for data entry such as keyboard, mouse, joystick and sound card. </li></ul>
  32. 32. Figure 3.4 Input devices in context
  33. 33. Input devices (Continued) <ul><li>Keyboard/keypad </li></ul><ul><li>Mouse – computers featuring a graphical user interface often require the use of a mouse or other pointing device. See Figure 3.5. </li></ul><ul><li>Lightpen – a pointing device that can be used to control applications by pointing to items on the screen. </li></ul><ul><li>Trackball – a pointing device that is controlled by rotating a small ball with the finger- tips or the palm of the hand. Moving the ball causes corresponding movement to a small pointer on the screen. Buttons are used to select items in the same way as with the mouse. </li></ul><ul><li>Joystick – is one of the most common input devices available and is primarily used for leisure activities such as playing computer games. </li></ul>
  34. 35. Input devices (Continued) <ul><li>Optical scanner is widely used for capturing graphics and text from printed documents. </li></ul><ul><ul><li>It can also be used to perform data entry by converting printed documents into text files that can be used by word processing packages and other programs. </li></ul></ul><ul><li>Optical character recognition (OCR) involves using software that attempts to recognize individual characters. </li></ul><ul><li>A variation on optical character recognition is optical mark recognition (OMR) which involves detecting and recognizing simple marks made on a document e.g. multiple choice answer sheet used in public examinations. </li></ul>
  35. 36. Input devices (Continued) <ul><li>Bar code reader is a means of displaying a unique identification number as a series of think and thin lines. The sequence and width of the lines in the bar code can be translated into a sequence of digits. </li></ul><ul><ul><li>Bar code numbers are normally produced according to a specific method. </li></ul></ul><ul><ul><li>The Universal Product Code , for example, is a standard method for creating and using bar codes. </li></ul></ul><ul><ul><li>A bar code reader measures the intensity of a light beam reflected from the printed bar code to identify the digits making up the unique identification number. </li></ul></ul><ul><ul><li>The digits making up the identification number are also printed at the foot of the bar code. </li></ul></ul><ul><ul><li>The most common example of the use of the bar code reader in industry is the supermarket checkout. </li></ul></ul>
  36. 38. Input devices (Continued) <ul><li>Touch screen is a transparent, pressure-sensitive covering that is attached to the screen of the monitor. </li></ul><ul><ul><li>Users make selection and control programs by pressing onto the screen. </li></ul></ul><ul><ul><li>Touch screens are comparatively expensive and require special software to operate. </li></ul></ul><ul><ul><li>Common applications for touch screens are interactive kiosks and bookings systems. </li></ul></ul>
  37. 39. Input devices (Continued) <ul><li>Graphics tablet is used in the same way as a writing pad. </li></ul><ul><ul><li>A stylus is used to draw images on a rigid pad located near to the computer. </li></ul></ul><ul><ul><li>As the user draws with the stylus, the image is duplicated on the computer’s display. </li></ul></ul>
  38. 40. Input devices (Continued) <ul><li>Video capture card records and stores video sequences (motion video) when connected to a digital video camera or other device. </li></ul><ul><ul><li>A playback device, e.g. a video cassette recorder, is connected to the video capture card and special software is used to capture, edit and manipulate video sequences. </li></ul></ul>
  39. 41. Input devices (Continued) <ul><li>Microphone/sound card </li></ul><ul><ul><li>A sound card can be used to capture sound, music and speech from a variety of sources. </li></ul></ul><ul><ul><li>A business application is the use of voice recognition software to dictate text directly into a word processing document. </li></ul></ul><ul><ul><li>The addition of a sound card and CD-ROM device provide a computer with multi-media facilities. </li></ul></ul><ul><li>Digital camera captures and stores still images. </li></ul><ul><ul><li>Images are held in the camera’s memory and stored on disk until they can be transferred to a personal computer. </li></ul></ul>
  40. 42. Input devices (Continued) <ul><li>Magnetic Ink Character Recognition (MICR) involves capturing data that has been printed using a special magnetic ink. </li></ul><ul><ul><li>This technology is normally associated with the banking industry, especially cheque processing. </li></ul></ul><ul><ul><li>Some of the details on a cheque, such as cheque number, are printed in a special typeface using magnetic ink. </li></ul></ul><ul><ul><li>The shape of each character means that it can be recognized by its magnetic field. </li></ul></ul>
  41. 43. Selecting input devices <ul><li>The selection of an input device is usually based upon three basic criteria: volume, speed and accuracy. </li></ul><ul><li>Volume </li></ul><ul><li>Record the details of payments made by customers  use more sophisticated methods such as OMR or OCR. </li></ul><ul><li>Fewer transactions  enter data using the keyboard as an input device. </li></ul>
  42. 44. Selecting input devices (Continued) <ul><li>Speed </li></ul><ul><li>Using OCR and OMR is faster than manual data entry methods </li></ul><ul><li>Accuracy </li></ul><ul><li>OCR is generally considered a comparatively unreliable means of entering data. </li></ul><ul><li>Error rate is the frequency of errors which occur when using an input device to recognize patterns. </li></ul>
  43. 45. Selecting input devices (Continued) <ul><li>Other considerations when selecting an input device are: </li></ul><ul><li>Complexity of data – data may need to be interpreted or altered before they are entered. </li></ul><ul><li>Cost – an organization may be unwilling or unable to purchase the hardware and software required. </li></ul><ul><li>Frequency of data entry – some types of data entry may be carried out on an infrequent or ad hoc basis. </li></ul>
  44. 46. Output devices <ul><li>Output devices display the results of computer processing. </li></ul><ul><li>The output produced by some devices is temporary in nature. </li></ul><ul><li>A display shown on a monitor when a new image is shown </li></ul><ul><li>A report produced on a printer is more permanent and may last for many years. </li></ul>
  45. 47. Figure 3.7 Output devices in context
  46. 48. Display devices <ul><li>The most common output device is almost certainly the monitor, formerly referred to as visual display unit (VDU) or CRT (cathode ray tube) , that is attached to all personal computer systems. </li></ul><ul><li>The quality of a monitor’s display can be described in several ways: </li></ul><ul><li>Resolution </li></ul><ul><li>Color depth </li></ul><ul><li>Dot pitch </li></ul><ul><li>Refresh rate </li></ul>
  47. 49. Display devices (Continued) <ul><li>Resolution </li></ul><ul><ul><li>The resolution of the monitor describes the fineness of the image that can be displayed. </li></ul></ul><ul><ul><li>Resolution is often expressed in terms of pixels (picture elements) – the individual dots that make up an image on the screen. </li></ul></ul><ul><ul><li>A 15” VGA monitor is able to display an image that is 640 by 480 pixels, 800 by 600 pixels or 1024 by 768 pixels in size. </li></ul></ul><ul><li>Color depth </li></ul><ul><ul><li>The number of colors that can be displayed on the screen is also related to resolution. </li></ul></ul><ul><ul><li>In Microsoft Windows, the typical number of colors that can be selected through the Control panel ranges from 2 (monochrome) through 16,256 to 32 million. </li></ul></ul>
  48. 50. Display devices (Continued) <ul><li>Dot pitch </li></ul><ul><ul><li>The quality of a monitor’s display involves measuring the distance between the pixels on the screen. </li></ul></ul><ul><ul><li>Such distance is called the dot pitch. </li></ul></ul><ul><ul><li>The smaller the distance between pixels, the finer the image will appear. </li></ul></ul><ul><ul><li>A dot pitch of 0.28mm is standard and will normally appear sharp and clear. </li></ul></ul>
  49. 51. Display devices (Continued) <ul><li>Refresh rate </li></ul><ul><ul><li>Another indicator of image quality relates to the way in which an image is displayed on the monitor. </li></ul></ul><ul><ul><li>The number of times the image is drawn upon the screen each second is known as the refresh rate and is measured in hertz. </li></ul></ul><ul><ul><li>A refresh rate of 60 Hz means that the image will be drawn upon the screen 60 times each second. </li></ul></ul>
  50. 52. Plotters <ul><li>A plotter uses a number of different colored pens to draw lines upon the paper as it moves through the machine. </li></ul><ul><li>The quality of text created is often very poor. </li></ul><ul><li>Plotters are primarily used to create technical drawings, such as engineering diagrams and to record the progress of continuous monitoring. </li></ul>
  51. 53. Printers <ul><li>Laser printer – A laser is used to charge sections of a rotating drum which is then used to print using toner powder achieving a combination of speed with high print quality. </li></ul><ul><li>Advantages of laser printer are: </li></ul><ul><li>Print quality </li></ul><ul><li>Speed </li></ul><ul><li>Volume </li></ul><ul><li>Noise </li></ul><ul><li>Disadvantages of laser printer are: </li></ul><ul><li>Cost of printing </li></ul><ul><li>Color printing </li></ul><ul><li>Cost </li></ul>
  52. 54. Printers <ul><li>Inkjet printer uses a print-head containing 50 or more small nozzles. Each nozzle can be controlled individually by electrostatic charges produced by the printer. </li></ul><ul><li>Characters are formed by squirting small droplets of ink directly onto the paper. </li></ul><ul><li>Advantages of inkjet printers include: </li></ul><ul><li>Cost </li></ul><ul><li>Reliability </li></ul><ul><li>Color printing </li></ul><ul><li>Versatility </li></ul><ul><li>Noise </li></ul><ul><li>Disadvantages of inkjet printers include: </li></ul><ul><li>Permanence </li></ul><ul><li>Print quality </li></ul><ul><li>Speed </li></ul>
  53. 55. Printers <ul><li>Dot-matrix printer – arranges a series of pins (usually from 8 to 24) to form the shape of a required character. </li></ul><ul><li>The character is transferred to the paper by striking the pins against an ink ribbon. This form of printing is known as impact printing. Dot-matrix printing is now only commonly used when carbon copies of a document need to be created. </li></ul><ul><li>Similarly, the daisywheel printer, now seldom used, functions in much the same way as a conventional typewriter. </li></ul>
  54. 56. Factors considered in selecting a printer <ul><li>Printing costs – the cost of printing is normally described in terms of cost per page . </li></ul><ul><li>Print quality – is normally measured in dots per inch (dpi). This describes the number of individual dots that can be printed within a space of one square inch. A typeset document is normally produced at a quality of between 1200 and 1500 dpi. The typical 600 dpi quality provided by a laser printer is considered acceptable. </li></ul><ul><li>Paper handling – the quantity of paper that a printer can hold is important. A large paper capacity reduces the need to refill the printer constantly. </li></ul><ul><li>Color printing – inkjet printers offer the best compromise between print quality and cost when producing documents in color. </li></ul><ul><li>Volume – the volume of printing has implications for running costs, maintenance costs and reliability. Dot-matrix printer (500 pages per month), laser printers (5,000 pages or higher per month). </li></ul><ul><li>Speed – printing speeds are usually measured in pages per minute (ppm). Typical examples of printing speeds are 1-2 ppm for an inkjet and 8 ppm and above for a laser printer. </li></ul>
  55. 57. Multi-function devices (MFDs) <ul><li>New printers that offer additional functions such as scanning, faxing and photocopying. </li></ul><ul><li>These printers, called multi-function devices (or MFDs), often come with an automatic document feeder, allowing them to scan, copy or fax as many as 50 pages at a time. </li></ul>
  56. 58. Selecting output devices <ul><li>Factors that should be considered when selecting an output device are: </li></ul><ul><li>Appropriateness </li></ul><ul><li>Permanence </li></ul><ul><li>Response time </li></ul><ul><li>Speed </li></ul><ul><li>Cost </li></ul>
  57. 59. Storage devices <ul><li>Storage devices (Figure 3.8) are used to store programs, data awaiting processing and the information resulting from computer processing. </li></ul><ul><li>Storages devices are categorized as primary storage when the data is loaded into computer memory or secondary storage when the data is stored on a separate device where the information will be retained even if the machine is switched off. </li></ul><ul><li>Floppy and hard disks are examples of secondary storage. </li></ul>
  58. 60. Figure 3.8 Storage devices in context
  59. 61. Units of data measurement <ul><li>A bit is a single binary digit and represents a 0 (zero) or a 1. The bit is the smallest unit of measurement. </li></ul><ul><li>A byte is made up of eight bits and represents a value between 0 and 255. A byte can be thought of as the amount of space required to hold a single character. </li></ul><ul><li>A kilobyte (KB) is approximately 1000 bytes. </li></ul><ul><li>A megabyte (MB) is approximately 1000 Kb. </li></ul><ul><li>A gigabyte (GB) is approximately 1000 Mb. </li></ul>
  60. 62. Secondary storage – floppy disk <ul><li>A floppy disk consists of a plastic disk, coated with a magnetic covering and enclosed within a rigid plastic case. </li></ul>
  61. 63. Secondary storage – hard disk drive <ul><li>Hard disk drives are a standard feature of a modern personal computer. </li></ul><ul><li>They are used to store the computer’s operating system, application software and data. </li></ul><ul><li>A hard disk drive (Figure 3.9) stores data upon a number of rigid platters that are rotated at very high speeds. Since the magnetic read/write heads float above the surface of the platter, the drive mechanism is enclosed within a vacuum to protect against dust and other contaminants. </li></ul>
  62. 64. Figure 3.9 Different views of the platters and sectors on hard disk drives
  63. 65. Secondary storage – flash drives <ul><li>A flash drive is a portable storage device that connects to a computer via a standard USB port. </li></ul><ul><li>Data are stored in flash memory, in an EEPROM (electrically erasable programmable read-only memory ) chip that can retain its contents for as long as ten years before it begins to degrade. </li></ul>
  64. 66. Secondary storage – CD-ROM <ul><li>The CD-ROM drive arose from the audio compact disc player and began to gain popularity during the late 1980s. </li></ul><ul><li>CD-ROM stands for “compact disc – read-only memory” denoting that CD-ROM discs are read-only devices. </li></ul><ul><li>The data on a compact disc are encoded as a series of dips and raised areas. These two states represent binary data – the same number system used by microprocessors. The player shines a laser beam onto the surface of the disc and measures the light that is reflected back. The intensity of the light that is reflected back enables the player to distinguish individual binary digits. </li></ul>
  65. 67. Secondary storage – CD-ROM <ul><li>Advantages of the compact disc are: </li></ul><ul><li>A compact disc has a very high storage capacity . A standard disc is able to store 650 Mb of data. This is equivalent to approximately 2 million pages of text or 74 minutes of high-quality music. </li></ul><ul><li>The costs associated with CD-ROM storage are typically very low. CD-ROM drives are inexpensive and can be repaired or replaced easily. </li></ul>
  66. 68. Secondary storage – CD-ROM <ul><li>Disadvantages of the compact disc are: </li></ul><ul><li>Compact discs are relatively fragile. They are easily damaged, for example by accidental scratches or exposure to heat. </li></ul><ul><li>CD-ROM is relatively slow in comparison to other storage devices such as the hard disk drive. </li></ul><ul><li>CD-ROM is a read-only medium. Although listed as a disadvantage, this can sometimes be seen as an advantage since unauthorized changes and accidental erasure of data can be prevented. </li></ul>
  67. 69. Secondary storage – CD-ROM <ul><li>A variation on the traditional CD-ROM drive is the CD-recordable (CDR) drive. </li></ul><ul><ul><li>These drives cannot only read conventional compact discs but can also write data to special gold or silvered-colored discs. </li></ul></ul><ul><ul><li>Compact discs produced in this way are known as write-once discs ( WORM ), that is, once data has been stored on the disc it cannot be altered or erased. </li></ul></ul><ul><li>A more recent development is the CD re-writable (CDRW) drive. In addition to providing the functionality of the CDR drive, the CDRW drive allows the use of special compact disc media that can be written and erased many times. </li></ul><ul><li>It is a cost-effective method of data backup of volumes previously only possible through tape backup. </li></ul>
  68. 70. Secondary storage – DVD <ul><li>Digital versatile disc (DVD) players began to gain popularity in 1997 and are now fitted as a standard component of many new personal computers. One common applications for DVD is as a distribution medium for full-length feature films. </li></ul><ul><li>DVD offers two important benefits to users. </li></ul><ul><ul><li>The disc used by a DVD player offer extremely high storage capacities, typically between 4 and 7 GB. </li></ul></ul><ul><ul><li>Data held on DVD can be accessed at very high speeds. </li></ul></ul>
  69. 71. Secondary storage – magnetic tape <ul><li>Tape streamer – A common form of storage device that used magnetic tape as a storage medium. </li></ul><ul><li>Major characteristics of magnetic tape include: </li></ul><ul><li>Magnetic tape allows only sequential access – data can only be accessed in strict order. </li></ul><ul><li>The costs associated with the use of magnetic tape as a storage medium are extremely low . </li></ul><ul><li>Storage devices based on magnetic tape are considered extremely slow . </li></ul><ul><li>Magnetic tape are mainly used for archiving and backup applications . </li></ul><ul><li>Magnetic tape is relatively fragile and is easily damaged. </li></ul>
  70. 72. Primary storage – memory <ul><li>There are two broad categories of computer memory: volatile and non-volatile . </li></ul><ul><li>The contents of volatile memory are lost when the power to the device is switched off. </li></ul><ul><li>Non-volatile memory retains its contents until changed in some way. </li></ul>
  71. 73. Random access memory (RAM) <ul><li>RAM is used as volatile , working storage, holding instructions and data that are waiting to be processed. </li></ul><ul><li>The contents of RAM are volatile, that is, any data held is lost when the power to the computer system is switched off. </li></ul><ul><li>A typical computer system will feature 128 or 256 Mb or more of RAM. </li></ul><ul><li>In general, the more RAM a computer system is equipped with, the faster it will operate and the more powerful it will be in terms of the complexity of the programs it can run. </li></ul><ul><li>RAM is also found in a number of other devices, for example in a printer RAM is used to store an image of the document to be printed. </li></ul>
  72. 74. Read-only memory (ROM) <ul><li>The contents of read-only memory (ROM) are fixed and cannot be altered. </li></ul><ul><li>ROM is non-volatile making it ideal as a means of storing the information needed for a device to function properly. </li></ul><ul><li>In a computer system, the basic information needed so that the computer can access disk drives and control peripherals is stored in ROM preventing users from accidentally deleting or altering information essential to the computer’s operation. </li></ul>
  73. 75. Selecting storage devices <ul><li>The selection of a storage device will normally be based upon speed, storage capacity and cost. </li></ul><ul><li>Speed </li></ul><ul><li>Capacity </li></ul><ul><li>Cost of storage </li></ul><ul><li>Other factors: </li></ul><ul><ul><li>Reliability of a storage device </li></ul></ul><ul><ul><li>Permanence of storage </li></ul></ul><ul><ul><li>Security measures </li></ul></ul>
  74. 76. Storage-type summary of selection criteria
  75. 77. Selecting storage devices <ul><li>Speed </li></ul><ul><li>The speed of a storage device is usually measured in terms of its access time (sometimes known as “seek time”) and data transfer rate. </li></ul><ul><li>The access time refers to the average time taken to locate a specific item of data. </li></ul><ul><ul><li>Access time are normally given in milliseconds, for example a typical hard disk drive might have an access time of 11ms </li></ul></ul><ul><ul><li>The data transfer rate describes how quickly the device is able to read continuous blocks of data. It is normally expressed in terms of kilobytes or megabytes. Typical data transfer rate for a CD-ROM drive might be given as 900 kb per second, while a hard disk drive might transfer more than 6 Mb per second. </li></ul></ul>
  76. 78. Selecting storage devices <ul><li>Capacity </li></ul><ul><li>The storage capacity of a given device will measured in kilobytes, megabytes or gigabytes. </li></ul><ul><li>In general, a fixed storage device will operate faster than one that uses removable media. </li></ul><ul><li>Many applications generate large data files that cannot be stored conveniently on removable media. </li></ul>
  77. 79. Selecting storage devices <ul><li>Cost of storage </li></ul><ul><li>The costs associated with storage devices are normally given in terms of cost per megabyte. </li></ul><ul><li>In some cases, the cost per megabyte is based upon the cost of the hardware (e.g. hard disk drive), in others it is based upon the cost of media (e.g. floppy disk). </li></ul>
  78. 80. Selecting storage devices <ul><li>Other factors </li></ul><ul><li>Reliability of a storage device </li></ul><ul><ul><li>A hardware failure might prevent all access to important business data. </li></ul></ul><ul><ul><li>Errors introduced when storing or reading data might also have serious consequences. </li></ul></ul><ul><li>Permanence of storage is important if there is a need to protect data from being deleted or altered. </li></ul><ul><li>Security measures are necessary to prevent data from being stolen or damaged. </li></ul><ul><ul><li>Removable media can be transported easily </li></ul></ul><ul><ul><li>Fixed devices are less vulnerable but also less versatile. </li></ul></ul>
  79. 81. Processors <ul><li>The Central Processing Unit (CPU) or processor – uses instructions from software to control the different components of a PC. </li></ul><ul><li>CPU found within a computer consists of two components: </li></ul><ul><ul><li>a control unit </li></ul></ul><ul><ul><li>an arithmetic logic unit (ALU). </li></ul></ul><ul><li>The control unit controls the operation of all hardware, including all input/output operations. </li></ul><ul><li>The ALU carries out arithmetical calculations, for example, addition and can also make comparisons between values. </li></ul>
  80. 83. Processors <ul><li>The speed of a processor will depend upon a number of different factors. </li></ul><ul><li>Two such factors are clock speed and bus width. </li></ul><ul><ul><li>The clock speed (measured in MHz) determines how many instructions per second the processor can execute. </li></ul></ul><ul><ul><li>The bus width describes how many pieces of data can be transmitted at one time. </li></ul></ul><ul><li>In both cases, the higher the value, the more powerful the processor. </li></ul><ul><li>For example, clock speeds for the Pentium range of processors have varied from 60 Mhz in early versions through to several GHz in more recent versions (Table 3.2). </li></ul>
  81. 84. Table 3.2 Historical improvements in processor capability Date Name Transistors and microns Clock speed in MHz MIPS (millions of instructions per second) 1974 8080 6k ,6 2 0.64 1979 8088 29k, 3 5 0.33 1982 ‘ 286 134k, 1.5 6 1 1985 ‘ 386 275k, 1.5 16 5 1993 Pentium 3.1M, 0.8 60 100 1997 Pentium II 7.5M, 0.35 233 400 1999 Pentium III 9.5M, 0.25 450 1000 2001 Pentium 4 42M, 0.18 1500 1500
  82. 85. Processors <ul><li>Not all aspects of performance of a computer are governed by the processor. </li></ul><ul><li>As a general rule, the faster the processor, the faster and more efficient the computer. </li></ul><ul><li>Virtual memory, RAM capacity, had-disk speed and graphics cards can also have a significant impact on overall system speed. </li></ul>
  83. 86. Graphics card <ul><li>A graphics card enables a computer to display text or graphics on a monitor. </li></ul><ul><li>The graphics card prepares and stores the image in memory prior to showing it on the screen. </li></ul><ul><li>When the image is complete, it is transmitted to the monitor and displayed. </li></ul>
  84. 87. Graphics card (Continued) <ul><li>Amount of memory available to a graphics card determines the maximum resolution of the image and how many colors can be displayed . </li></ul><ul><li>All graphics cards support the VGA (video graphics array) standard which specifies a maximum range size of 640 by 320 pixels, displayed in 16 colors. </li></ul><ul><li>A VGA display can be achieved with just 256 kb of memory but larger images with more colors can require 1 Mb of memory or more. </li></ul><ul><li>Many graphics cards are supplied with 64 Mb, 128 Mb, or even 256 Mb of memory, allowing them to display very complex images at large sizes. </li></ul>
  85. 88. Graphics card standards
  86. 89. Motherboard <ul><li>The motherboard (Figure 3.12) is the main circuit board within a computer and houses the processor, memory, expansion slots and a number of connectors used for attaching additional devices, such as a hard disk drive. Any device that forms part of the motherboard is able to communicate with the processor directly. </li></ul><ul><li>The motherboard will contain a ROM chip that holds the computer’s BIOS. The BIOS (basic input/output system) contains software that controls all of the computer’s most basic activities. </li></ul><ul><li>It is the BIOS that allows the keyboard, display, hard disk drives, serial ports and other devices to function. </li></ul><ul><li>The BIOS is stored in ROM so that it is always available and cannot be accidentally damaged or erased. </li></ul>
  87. 91. Motherboard (Continued) <ul><li>Storage devices, such as hard disk drives, are attached via the motherboard’s I/O (input/output) connections. </li></ul><ul><li>At least two serial ports are also supported, allowing mouse, modems, printers and a range of other devices to be connected. </li></ul><ul><li>In addition, a parallel port is normally used to connect a printer, scanner or other device. </li></ul><ul><li>Expansion slots allow additional devices to be connected to the computer. </li></ul><ul><li>A computer’s capabilities can be extended by adding special circuit boards (known as expansion cards) to the motherboard. </li></ul><ul><li>Common expansion cards include graphics card, modems and sound cards (Figure 3.13) </li></ul><ul><li>A typical computer will feature up to six expansion slots. </li></ul>
  88. 92. Figure 3.13 A typical expansion card for use with a personal computer
  89. 93. Selecting hardware suppliers <ul><li>The process of selecting a supplier for hardware is often known as vendor analysis . </li></ul><ul><li>Large purchases may involve the organization in producing a tender document . </li></ul><ul><li>A tender document is an invitation to suppliers, asking them to bid for the right to supply an organization’s hardware, software and other requirements. </li></ul><ul><li>An organization selects a supplier by examining each response to the invitation to tender in detail. </li></ul>
  90. 94. Tenders <ul><li>Tender documents will ask for important information about potential suppliers. </li></ul><ul><li>Size of the organization (staffing, premises, turnover, etc.) </li></ul><ul><li>Number of years of experience </li></ul><ul><li>Details of any major projects undertaken </li></ul><ul><li>Details of any previous customers who may be willing to provide references. </li></ul>
  91. 95. Evaluating proposals <ul><li>There are three basic criteria for evaluating a supplier’s proposals. These are based on technical, cost and support issues . </li></ul><ul><li>Technical issues refer to the extent to which the proposal satisfies the hardware and software requirements set out in the tender document or statement of requirements. They include: </li></ul><ul><ul><li>Performance : whether or not hardware will perform as specified. </li></ul></ul><ul><ul><li>Compatibility : equipment is compatible with the company’s existing systems, particularly any software packages already in use. </li></ul></ul>
  92. 96. Evaluating proposals (Continued) <ul><li>Cost issues describe the overall cost of the project, including: installation, ongoing maintenance and factors involving methods of finance. </li></ul><ul><li>Consideration must be given to different costs associated with the purchase of a new computer system. </li></ul><ul><ul><li>Initial cost covers the purchase of hardware, installation and training. </li></ul></ul><ul><ul><li>Ongoing costs include insurance and maintenance and are paid over the life of the system. Ongoing costs are known as the “total cost of ownership” (TCO). </li></ul></ul>
  93. 97. Evaluating proposals (Continued) <ul><li>Support issues describe the reputation of the supplier in terms of their ability to provide adequate support, training, advice, repairs and maintenance. </li></ul><ul><li>Training – offer a range of training courses that cater for mixed abilities and enable users to reach different levels of competence. </li></ul><ul><li>Maintenance --- suppliers should guarantee that important repairs are carried out within a fixed time period. </li></ul><ul><li>Implementation – The use of a single supplier can ensure that the project runs more smoothly and simplifies the division of responsibilities. </li></ul><ul><li>Backup facilities – a backup or disaster recovery site reproduces an organization’s computing facilities in order to provide a measure of protection against a major breakdown. </li></ul>
  94. 98. Evaluation methods <ul><li>Benchmarking describe the process of testing the performance of computer equipment. </li></ul><ul><ul><li>Having carried out a series of benchmark tests, the results can be compared against similar items in order to make the best selection. </li></ul></ul><ul><li>Scoring systems </li></ul><ul><ul><li>The requirements are used to devise a list of criteria for the selection of a given piece of hardware or a supplier. </li></ul></ul><ul><ul><li>The relative importance of each factor is determined by a weighting factor. </li></ul></ul><ul><ul><li>Each item or supplier is assigned a series of scores based on the criteria in the weighted ranking table. </li></ul></ul><ul><ul><li>The total score for each item or supplier is calculated and used as the basis for final selection. </li></ul></ul>
  95. 99. Evaluating proposals (Continued)

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