08/16/1308/16/13 11
Input & Output DevicesInput & Output Devices
08/16/13 2
Input DevicesInput Devices
 Input devices are used to feed data and
instructions to the computer systems.
 Th...
08/16/13 3
Input DevicesInput Devices
 The form of the input devices :
 Keyboard, Pointing device
 Writing & drawing in...
08/16/13 4
Key board
 It’s similar as normal typewriter
keyboard, plus a number of special keys.
 Standard keys are used...
08/16/13 5
Key board
 Cursor-movement key
 104-key enhanced keyboard
 Used for data entry and to issue commands
into th...
08/16/13 6
Traditional KeyboardTraditional Keyboard
08/16/13 7
Pointing device - Mouse
 A mouse is a device that can be rolled on a
desktop to direct a pointer (cursor) on t...
08/16/13 8
08/16/13 9
Pointing device - Mouse
 Command Actions
 Point - an act of moving the pointing
device to an object on-screen...
08/16/13 10
Pointing device - Trackball
 A trackball performs like a stationary, upside-
down mouse.
 Most portable lapt...
08/16/13 11
Pointing device - Joystick
 A joystick is a small lever that
can be moved in any direction
to move an object ...
08/16/13 12
Graphics Input - Scanner
 Image scanners or graphic
scanners convert the printed or
photographic image on pap...
08/16/13 13
Text Input - Scanner
 Text are scanned from the printed page
into the computer, as an attempt to reduce
error...
08/16/13 14
Text Input - OCR
 Optical Character Recognition (OCR)
 An input device that can read and recognise
the symbo...
08/16/13 15
Writing & Drawing Input
Devices - Light Pen
 The light pen is a light sensitive stylus, or pen
like device, c...
08/16/13 16
08/16/13 17
Writing & Drawing Input
Devices - Touch Screen
 The touch screen is
video display screen
that has been sensit...
08/16/13 18
Writing & Drawing Input
Devices - Digitizing Tablet
 A digitizing tablet consists of a tablet
connected by a ...
08/16/13 19
Writing & Drawing Input
Devices - Digitizing Tablet
 More sophisticated
stylus or pointing
devices with high
...
08/16/13 20
Video input
(Digital Camera)
 As with sound, most films & video are
generated and recorded in analog forms in...
08/16/13 21
08/16/13 22
Video input
 Two type of video cards:
 Frame grabber video card
• Can capture & digitize only a single frame...
08/16/13 23
Voice input
(Voice Recognition)
 Converts the person’s
speech in to digital code
by comparing the
electrical ...
08/16/13 24
Source Data Input - MICR
 Magnetic Ink Character Recognition (MICR)
 MICR characters which are printed with ...
08/16/13 25
Source Data Input – Magnetic strip
 Used on the backs of credit cards and bank
debit cards, and various other...
08/16/13 26
Source Data Input - OMR
 Optical-Mark Recognition (OMR)
 An input device that senses marks on a piece
of pap...
08/16/13 27
Source Data Input - Bar codes
 Commonly used by
sales and stock people
in retail stores and
supermarkets.
 P...
08/16/13 28
Output devicesOutput devices
 Translate information processed by the
computer into a form that human or anoth...
08/16/13 29
Output devicesOutput devices
 There are several ways
to produce output:
 Text output
 Graphics output
 Sou...
08/16/13 30
Output devicesOutput devices
 Text Output :
 Simply the alphanumeric characters that
make up our language. T...
08/16/13 31
Output devicesOutput devices
 Graphics Output :
 Includes line drawings, maps, presentations
business graphi...
08/16/13 32
Output devicesOutput devices
 Sound output :
 Ranges from the message beeps produced
by the computer system ...
08/16/13 33
Output devicesOutput devices
 Video output :
 Photographs (still images) or moving
images such as television...
08/16/13 34
PrintersPrinters
 A printer provides hard copy output on paper.
The basic criteria for evaluating printers
in...
08/16/13 35
 Translates information that has been processed byTranslates information that has been processed by
the syste...
08/16/13 36
PrintersPrinters
 Impact Printers :
 Form characters or images by striking a
mechanism such as print hammer ...
08/16/13 37
Impact PrintersImpact Printers
 First printing technology.
E.g. 24 Pin Okidata Dot Matrix Printers - 475 cps
...
08/16/13 38
Impact PrintersImpact Printers
 Followed by dot-matrix printers.
 Dot-matrix output is produced by printers ...
08/16/13 39
Non-Impact Printers –Non-Impact Printers –
Laser PrintingLaser Printing
 Provide high-quality non-impact prin...
08/16/13 40
Non-Impact Printers –Non-Impact Printers –
Laser PrintingLaser Printing
 Excellent print quality and font sel...
08/16/13 41
Non-Impact Printers –Non-Impact Printers –
Inkjet PrintingInkjet Printing
 Inkjet printer transfers character...
08/16/13 42
PlottersPlotters
 It is a specialized output device designed to produce
high-quality graphics in a variety of...
08/16/13 43
MonitorsMonitors
 Known as screens orKnown as screens or
display screensdisplay screens
 Output referred to ...
08/16/13 44
 Cathode-ray tubeCathode-ray tube oror
CRTsCRTs
 Flat-panelFlat-panel
• Require less power toRequire less po...
08/16/13 45
Video MonitorVideo Monitor
 Provides soft copy output.
 Comes in either monochrome
or colour.
 A monochrome...
08/16/13 46
Video DisplaysVideo Displays
 Resolution - describes the degree of
details in a video display.
 The higher t...
08/16/13 47
Video DisplaysVideo Displays
 Bit-mapped display offers extremely
high-resolution. Bit map means that each
do...
08/16/13 48
Video DisplaysVideo Displays
 The liquid crystal display (LCD) is a
flat-screen display commonly used with
po...
08/16/13 49
TerminalTerminal
 A monitor-keyboard combination.
 Has no system unit of its own, but instead uses
the facil...
08/16/13 50
TerminalTerminal
 Dumb terminal performs the simplest input
and output operations but no processing.
e.g. A b...
08/16/13 51
Optical Storage DevicesOptical Storage Devices
 Data recording is done by using laser technology.Data recordi...
08/16/13 52
CD-ROMCD-ROM
 Holds approximately 650 MBHolds approximately 650 MB
 Used for :Used for :
 Data StorageData ...
08/16/13 53
DVD DevicesDVD Devices
 OriginallyOriginally- Digital Video Disk (DVD)- Digital Video Disk (DVD)
 NowNow - D...
08/16/13 54
Removable media drivesRemovable media drives
 Including tape drives, zip, LS120, and DAT drivesIncluding tape...
08/16/13 55
Magnetic TapesMagnetic Tapes
 Tape width = ½ inchTape width = ½ inch
 Data storage in tracksData storage in ...
08/16/13 56
Magnetic TapesMagnetic Tapes
 Time to write a block = 128 msTime to write a block = 128 ms
 Tape start/stop ...
08/16/13 57
Digital TapeDigital Tape
 Magnetic tapeMagnetic tape
 A tape made of thin plastic with a magneticallyA tape ...
08/16/13 58
ZIP DevicesZIP Devices
 Zip drive (portable or internal) uses a special 3.5 inchZip drive (portable or intern...
08/16/13 59
Hard Disk Drive (HDD)Hard Disk Drive (HDD)
 The mechanism that reads and writes data on a hardThe mechanism t...
08/16/13 60
Hard Disk Drive OperationHard Disk Drive Operation
 HDD consists of spinning disks with headsHDD consists of ...
08/16/13 61
Magnetic Disk (Hard Disk)Magnetic Disk (Hard Disk)
 Removable Disk :Removable Disk :
 Removable disk pack us...
08/16/13 62
Magnetic DiskMagnetic Disk
 A disk starts out very unstructured – just a lot of bitsA disk starts out very un...
08/16/13 63
Magnetic DiskMagnetic Disk
 Formatting organises disks into numbered ringsFormatting organises disks into num...
08/16/13 64
Magnetic DiskMagnetic Disk
For an example,For an example,
 Disk packDisk pack = 20 surfaces = 11 Platters= 20...
08/16/13 65
Magnetic DiskMagnetic Disk
 The time required to position the read-write heads over theThe time required to p...
08/16/13 66
Hard Disk DriveHard Disk Drive
08/16/13 67
Hard Disk Technology –Hard Disk Technology –
RAID SystemsRAID Systems
 Stands for Redundant Array of Independ...
08/16/13 68
RAID SystemsRAID Systems
 RAID functions are:RAID functions are:
 Immediate availability of data and, depend...
08/16/13 69
RAID SystemsRAID Systems
 The array includes drives, controllers, enclosure,The array includes drives, contro...
08/16/13 70
ModemsModems
 A device used to provide remote connectivity over the
Telephone lines.
 For two modems to comm...
08/16/13 71
ModemsModems
 Connection of informationConnection of information
superhighway is by way of a modem.superhighw...
08/16/13 72
ModemsModems
 It converts digital data used by the computers intoIt converts digital data used by the compute...
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2. input output storage

  1. 1. 08/16/1308/16/13 11 Input & Output DevicesInput & Output Devices
  2. 2. 08/16/13 2 Input DevicesInput Devices  Input devices are used to feed data and instructions to the computer systems.  They consist of a range of devices that take data and programs from the outside world that people can read or comprehend and convert them to a form that the computer can manipulate.
  3. 3. 08/16/13 3 Input DevicesInput Devices  The form of the input devices :  Keyboard, Pointing device  Writing & drawing input devices  Video, Text, voice input
  4. 4. 08/16/13 4 Key board  It’s similar as normal typewriter keyboard, plus a number of special keys.  Standard keys are used to enter words & numbers. Special keys so called “function keys” labeled as F1,F2 ... are used to enter commands.  A numeric keypad that resembles an electronic calculator’s keypad.
  5. 5. 08/16/13 5 Key board  Cursor-movement key  104-key enhanced keyboard  Used for data entry and to issue commands into the system.
  6. 6. 08/16/13 6 Traditional KeyboardTraditional Keyboard
  7. 7. 08/16/13 7 Pointing device - Mouse  A mouse is a device that can be rolled on a desktop to direct a pointer (cursor) on the computers display screen. The cursor is the symbol on the screen that shows where data may be entered next or the command to be activated.  Pointing devices commonly have two or three buttons that are used to issue commands to the computer.
  8. 8. 08/16/13 8
  9. 9. 08/16/13 9 Pointing device - Mouse  Command Actions  Point - an act of moving the pointing device to an object on-screen.  Click - select the object on-screen.  Drag - holding down the pointing-device button while moving the selected object on- screen.
  10. 10. 08/16/13 10 Pointing device - Trackball  A trackball performs like a stationary, upside- down mouse.  Most portable laptop computers use a built-in or clip-on trackball.
  11. 11. 08/16/13 11 Pointing device - Joystick  A joystick is a small lever that can be moved in any direction to move an object on the screen.  Usually associated with playing computer games.
  12. 12. 08/16/13 12 Graphics Input - Scanner  Image scanners or graphic scanners convert the printed or photographic image on paper into electronic signals and then into digital form.  These digital information then can be stored in a computer & manipulated.
  13. 13. 08/16/13 13 Text Input - Scanner  Text are scanned from the printed page into the computer, as an attempt to reduce errors in data entry while speeding up the process as well.  The software incorporated converts the scanned images into character codes and thus enables text processing.
  14. 14. 08/16/13 14 Text Input - OCR  Optical Character Recognition (OCR)  An input device that can read and recognise the symbols of text (special printed characters) & convert them to the machine readable form.
  15. 15. 08/16/13 15 Writing & Drawing Input Devices - Light Pen  The light pen is a light sensitive stylus, or pen like device, connected by a wire to the computer terminal.  The user brings the pen to a desired point on the display screen and presses the pen button, which identifies that screen location to the computer.
  16. 16. 08/16/13 16
  17. 17. 08/16/13 17 Writing & Drawing Input Devices - Touch Screen  The touch screen is video display screen that has been sensitized to receive input from the touch of a finger.
  18. 18. 08/16/13 18 Writing & Drawing Input Devices - Digitizing Tablet  A digitizing tablet consists of a tablet connected by a wire to a stylus or puck.  A stylus is a pen like device with which the user “sketches” an image.  A puck is a copying device with which the user copies an image as it is moved over a desired path on a sketch.
  19. 19. 08/16/13 19 Writing & Drawing Input Devices - Digitizing Tablet  More sophisticated stylus or pointing devices with high accuracy are used by designers, architects, artists, desktop publishers, map makers, etc.
  20. 20. 08/16/13 20 Video input (Digital Camera)  As with sound, most films & video are generated and recorded in analog forms in which the signals are in continuously varying nature. Thus the signals come from the systems such as VCR, videodisk or laser disk, or a camcorder must be converted to digital form through a special video capture card installed in the computer.
  21. 21. 08/16/13 21
  22. 22. 08/16/13 22 Video input  Two type of video cards:  Frame grabber video card • Can capture & digitize only a single frame at a time.  Full motion video card • Can convert analog to digital signals at the rate of 30 frames per second, giving the effect of a continuously following motion picture.
  23. 23. 08/16/13 23 Voice input (Voice Recognition)  Converts the person’s speech in to digital code by comparing the electrical patterns produce by the speaker’s voice with a set of prerecorded patterns stored in the computer.
  24. 24. 08/16/13 24 Source Data Input - MICR  Magnetic Ink Character Recognition (MICR)  MICR characters which are printed with magnetic ink , containing magnetic particles are read by MICR equipment producing digitised signals.  Used by banks to read the information such as printed serial numbers on the bottom of cheques using magnetic ink.  MICR reader/sorter can process cheques and other documents at speeds of up to 2000 documents per minute.
  25. 25. 08/16/13 25 Source Data Input – Magnetic strip  Used on the backs of credit cards and bank debit cards, and various other plastic cards.  Enables readers, such as automated teller machines (ATM) to read account information.
  26. 26. 08/16/13 26 Source Data Input - OMR  Optical-Mark Recognition (OMR)  An input device that senses marks on a piece of paper, using a light beam, and converts them into electronic signals which are sent to the computer for processing.  Commonly used to mark the questionnaires or school examination answer sheets where the students, using pencils mark certain boxes on the examination answer sheets provided.
  27. 27. 08/16/13 27 Source Data Input - Bar codes  Commonly used by sales and stock people in retail stores and supermarkets.  Point-of-sale (POS) terminal scans the bar codes of the Universal Product Code (UPC) to register the price, which is programmed into the host computer, as well as to deduct the item from stock.
  28. 28. 08/16/13 28 Output devicesOutput devices  Translate information processed by the computer into a form that human or another machine can recognize.  The two principle kind of outputs are hardcopy & softcopy .  Hardcopy refers to a printed output.  Softcopy refers to the information that is shown on the display screen or is in audio or video form.
  29. 29. 08/16/13 29 Output devicesOutput devices  There are several ways to produce output:  Text output  Graphics output  Sound output  Video output
  30. 30. 08/16/13 30 Output devicesOutput devices  Text Output :  Simply the alphanumeric characters that make up our language. Text output appearance ranges from typewritten to typeset quality.
  31. 31. 08/16/13 31 Output devicesOutput devices  Graphics Output :  Includes line drawings, maps, presentations business graphics, computer-aided design, computer painting, photographic reproduction.
  32. 32. 08/16/13 32 Output devicesOutput devices  Sound output :  Ranges from the message beeps produced by the computer system to the human voice to music and other forms of sound.
  33. 33. 08/16/13 33 Output devicesOutput devices  Video output :  Photographs (still images) or moving images such as television and videotaped material.
  34. 34. 08/16/13 34 PrintersPrinters  A printer provides hard copy output on paper. The basic criteria for evaluating printers include:  QualityQuality of the printed output.  SpeedSpeed at which printed pages are produced.  SoundSound levellevel during printing.  CostCost of printing media (ribbons, cartridges).  ConservationConservation of paper.
  35. 35. 08/16/13 35  Translates information that has been processed byTranslates information that has been processed by the system unitthe system unit  OutputOutput referred to as hard copyreferred to as hard copy  FeaturesFeatures • ResolutionResolution • Color capabilityColor capability • SpeedSpeed • MemoryMemory
  36. 36. 08/16/13 36 PrintersPrinters  Impact Printers :  Form characters or images by striking a mechanism such as print hammer or wheel against an inked ribbon leaving an image on paper. Make high noise. Now used less.  Non- Impact Printers :  Form characters or images without making direct physical contact between printing mechanism and paper.
  37. 37. 08/16/13 37 Impact PrintersImpact Printers  First printing technology. E.g. 24 Pin Okidata Dot Matrix Printers - 475 cps  Early days typewriters were adapted, produced same high-quality output.  Cannot change fonts nor can print graphics or colours. Only the symbols available in the printing mechanism can be produced on the paper. e.g. daisy wheel printer, drum and belt printers.
  38. 38. 08/16/13 38 Impact PrintersImpact Printers  Followed by dot-matrix printers.  Dot-matrix output is produced by printers that use wires in the print head. These wires extend out in different patterns, pressing against the ribbon to print the characters on paper. As this mechanism enables the print control up to the dot level on the paper, the can be used to produce both text and graphics.  Fast, but noisy. Wear out ribbons very quickly.
  39. 39. 08/16/13 39 Non-Impact Printers –Non-Impact Printers – Laser PrintingLaser Printing  Provide high-quality non-impact printing. Output is created by directing a laser beam onto a drum to create an electrical charge that forms a pattern of letters or images.  As the drum rotates, it picks up black toner on the images and transfers them to paper. The heating process then fixes the toner particles permanently on the paper.
  40. 40. 08/16/13 40 Non-Impact Printers –Non-Impact Printers – Laser PrintingLaser Printing  Excellent print quality and font selection.  Fast printing. E.g. 8-500 pages per minute  High quality graphics with colour. High resolution.  Medium level noise, but high cost.  Primary disadvantages are expensive maintenance and the high cost of toner cartridges.
  41. 41. 08/16/13 41 Non-Impact Printers –Non-Impact Printers – Inkjet PrintingInkjet Printing  Inkjet printer transfers characters and images to paper by spraying a fine jet of ink.  Offers nearly the quality of laser printing, but not the speed. Low-cost alternative for high quality printing.
  42. 42. 08/16/13 42 PlottersPlotters  It is a specialized output device designed to produce high-quality graphics in a variety of colours. That are especially useful for creating maps and architectural drawings, although they may also produce less complicated charts and graphics.  Type of plotters :  Pen plotter  Electrostatic plotter  Thermal plotter
  43. 43. 08/16/13 43 MonitorsMonitors  Known as screens orKnown as screens or display screensdisplay screens  Output referred to asOutput referred to as soft copysoft copy  FeaturesFeatures • Resolution-pixelsResolution-pixels • Dot pitchDot pitch • Refresh rateRefresh rate • SizeSize
  44. 44. 08/16/13 44  Cathode-ray tubeCathode-ray tube oror CRTsCRTs  Flat-panelFlat-panel • Require less power toRequire less power to operateoperate • Portable and thinner thanPortable and thinner than CRTsCRTs  Other monitorsOther monitors • E-booksE-books • Data projectorsData projectors • High-definition televisionHigh-definition television (HDTV)(HDTV)
  45. 45. 08/16/13 45 Video MonitorVideo Monitor  Provides soft copy output.  Comes in either monochrome or colour.  A monochrome display a single colour against a different coloured background, such as green on black amber on black or white on black.  Colour display can show a variety of colours.
  46. 46. 08/16/13 46 Video DisplaysVideo Displays  Resolution - describes the degree of details in a video display.  The higher the resolution the characters and images are sharper and crisper as film image.  Conventional television display is low resolution as we can see lines, jagged edges and graininess in the image.
  47. 47. 08/16/13 47 Video DisplaysVideo Displays  Bit-mapped display offers extremely high-resolution. Bit map means that each dot on the screen, called a pixel (for picture element) is represented by one bit (a 1 or 0) by the computer. (monochrome)  Bit-mapped graphics is the colour version of a bit map display. Each pixel identifies a number (e.g. 1-256 on a 256-colour palette) indicating what colour that pixel should be.
  48. 48. 08/16/13 48 Video DisplaysVideo Displays  The liquid crystal display (LCD) is a flat-screen display commonly used with portable computers.
  49. 49. 08/16/13 49 TerminalTerminal  A monitor-keyboard combination.  Has no system unit of its own, but instead uses the facility from a central computer via a communication link.  Mainframes, minicomputers and workstation systems support multiple terminals.
  50. 50. 08/16/13 50 TerminalTerminal  Dumb terminal performs the simplest input and output operations but no processing. e.g. A bank ATM  Smart (intelligent) terminal may have its own CPU or processing capabilities, as well as built-in disk for storage. e.g. Point-of-sale (POS) cash register
  51. 51. 08/16/13 51 Optical Storage DevicesOptical Storage Devices  Data recording is done by using laser technology.Data recording is done by using laser technology.  Types of Optical Storage Devices :Types of Optical Storage Devices :  Compact Disk Read Only Memory (CD-ROM)Compact Disk Read Only Memory (CD-ROM)  Compact Disk Recordable drives (CD-R)Compact Disk Recordable drives (CD-R)  CD-ROM PlayersCD-ROM Players  CD-ROM TowersCD-ROM Towers  Erasable Optical Disk (EOD)Erasable Optical Disk (EOD)  CD-ROM JukeboxesCD-ROM Jukeboxes  DVD-ROM DrivesDVD-ROM Drives  Magneto-optical DrivesMagneto-optical Drives  Optical storage mediaOptical storage media
  52. 52. 08/16/13 52 CD-ROMCD-ROM  Holds approximately 650 MBHolds approximately 650 MB  Used for :Used for :  Data StorageData Storage  EncyclopaediasEncyclopaedias  CataloguesCatalogues  GamesGames  EntertainmentEntertainment  MoviesMovies  Magazines and booksMagazines and books
  53. 53. 08/16/13 53 DVD DevicesDVD Devices  OriginallyOriginally- Digital Video Disk (DVD)- Digital Video Disk (DVD)  NowNow - Digital Versatile Disk (DVD)- Digital Versatile Disk (DVD)  Refers to a storage medium that can store TV-qualityRefers to a storage medium that can store TV-quality images on a CD-ROM disk with a capacity exceedingimages on a CD-ROM disk with a capacity exceeding 5 GB.5 GB.
  54. 54. 08/16/13 54 Removable media drivesRemovable media drives  Including tape drives, zip, LS120, and DAT drivesIncluding tape drives, zip, LS120, and DAT drives except floppy drives.except floppy drives.  Magnetic TapesMagnetic Tapes  Very popular with mainframe computers.Very popular with mainframe computers.  Storage density is expressed in ‘bytes per inch’Storage density is expressed in ‘bytes per inch’ ((bpibpi) or character per inch () or character per inch (cpicpi).).  Storage density varies with the quality of theStorage density varies with the quality of the tape & the equipment used to read form andtape & the equipment used to read form and write on it.write on it.
  55. 55. 08/16/13 55 Magnetic TapesMagnetic Tapes  Tape width = ½ inchTape width = ½ inch  Data storage in tracksData storage in tracks  Tape tracks = 9Tape tracks = 9  Data recorded in blocks of charactersData recorded in blocks of characters  Read/write speed = 50 ips (inches per second)Read/write speed = 50 ips (inches per second)  Recording density = 1,600 bpi (bytes per inch)Recording density = 1,600 bpi (bytes per inch)  Tape length = 2400 feet = 28,800 inchesTape length = 2400 feet = 28,800 inches  Storage capacityStorage capacity 40 MB40 MB
  56. 56. 08/16/13 56 Magnetic TapesMagnetic Tapes  Time to write a block = 128 msTime to write a block = 128 ms  Tape start/stop time = 0.02 sec = 20 msTape start/stop time = 0.02 sec = 20 ms  Time to write a block + start and stop timesTime to write a block + start and stop times = 20 + 128 + 20 = 168 ms= 20 + 128 + 20 = 168 ms
  57. 57. 08/16/13 57 Digital TapeDigital Tape  Magnetic tapeMagnetic tape  A tape made of thin plastic with a magneticallyA tape made of thin plastic with a magnetically layer on which data can be stored.layer on which data can be stored.  Digital tape store data in digital format, instead ofDigital tape store data in digital format, instead of analogue format.analogue format.
  58. 58. 08/16/13 58 ZIP DevicesZIP Devices  Zip drive (portable or internal) uses a special 3.5 inchZip drive (portable or internal) uses a special 3.5 inch disk that holds 100 Mb or 250 MB.disk that holds 100 Mb or 250 MB.
  59. 59. 08/16/13 59 Hard Disk Drive (HDD)Hard Disk Drive (HDD)  The mechanism that reads and writes data on a hardThe mechanism that reads and writes data on a hard disk.disk.  A sealed unit that a PC uses for nonvolatile dataA sealed unit that a PC uses for nonvolatile data storage.storage.  HDDs are sometimes calledHDDs are sometimes called Winchester drives.Winchester drives.  Used to store crucial programming and data.Used to store crucial programming and data.  Contains rigid, disk-shaped platters, usuallyContains rigid, disk-shaped platters, usually constructed of aluminum or glass.constructed of aluminum or glass.  Many disk drives improve their performance through aMany disk drives improve their performance through a technique calledtechnique called cachingcaching..
  60. 60. 08/16/13 60 Hard Disk Drive OperationHard Disk Drive Operation  HDD consists of spinning disks with headsHDD consists of spinning disks with heads that move over the disk and store data inthat move over the disk and store data in tracks and sectors.tracks and sectors.  The heads read and write data in concentricThe heads read and write data in concentric rings called tracks.rings called tracks.  Tracks are divided into segments calledTracks are divided into segments called sectors which store 512 bytes.sectors which store 512 bytes.  Disk consists of several platters (e.g. 3).Disk consists of several platters (e.g. 3). Each platter has two sides. A number refersEach platter has two sides. A number refers to each side (e.g. side 0, 1, 2, 3 for 4to each side (e.g. side 0, 1, 2, 3 for 4 surfaces). A Disc pack may have 20 surfacessurfaces). A Disc pack may have 20 surfaces or = 11 Plattersor = 11 Platters  The platters can’t bend or flex.The platters can’t bend or flex.
  61. 61. 08/16/13 61 Magnetic Disk (Hard Disk)Magnetic Disk (Hard Disk)  Removable Disk :Removable Disk :  Removable disk pack used in earlier Mainframe &Removable disk pack used in earlier Mainframe & Mini Computers.Mini Computers.  Disk cartridge - easy to remove like cassettes.Disk cartridge - easy to remove like cassettes.  Fixed Disk :Fixed Disk :  Installed in a sealed container and it’s notInstalled in a sealed container and it’s not removable.removable.  most of the fixed disks use the “Winchester”most of the fixed disks use the “Winchester” technology.technology.
  62. 62. 08/16/13 62 Magnetic DiskMagnetic Disk  A disk starts out very unstructured – just a lot of bitsA disk starts out very unstructured – just a lot of bits of magnetic stuff without any organisation, rhyme orof magnetic stuff without any organisation, rhyme or reason. Before the system can start writing records toreason. Before the system can start writing records to it, the disk must have a structure a grid work intoit, the disk must have a structure a grid work into which the information can be placed.which the information can be placed.  Formatting a disk is the process of putting the gridFormatting a disk is the process of putting the grid work on the disk and building the organisationalwork on the disk and building the organisational structure so that file can be found. Once a disk isstructure so that file can be found. Once a disk is formatted it is ready for the system to write data to it.formatted it is ready for the system to write data to it.
  63. 63. 08/16/13 63 Magnetic DiskMagnetic Disk  Formatting organises disks into numbered ringsFormatting organises disks into numbered rings called cylinders. A cylinder on a single side iscalled cylinders. A cylinder on a single side is referred to as a track.referred to as a track.  Each track is broken into numbered pie slices calledEach track is broken into numbered pie slices called sectors. Each sector stores information.sectors. Each sector stores information.
  64. 64. 08/16/13 64 Magnetic DiskMagnetic Disk For an example,For an example,  Disk packDisk pack = 20 surfaces = 11 Platters= 20 surfaces = 11 Platters  Disk = 2048 cylinders (figure has only 4)Disk = 2048 cylinders (figure has only 4)  Cylinder = 20 tracks (track in each surface)Cylinder = 20 tracks (track in each surface)  Track = 72 sectors (figure outermost has 13)Track = 72 sectors (figure outermost has 13)  Sector = 512 bytesSector = 512 bytes  Disk Storage = 512 * 72 * 20 * 2048 bytes = 1.44 GBDisk Storage = 512 * 72 * 20 * 2048 bytes = 1.44 GB  Rotational speed = 3600 rpm (revolutions per minute)Rotational speed = 3600 rpm (revolutions per minute) = 16.66 ms per revolution= 16.66 ms per revolution
  65. 65. 08/16/13 65 Magnetic DiskMagnetic Disk  The time required to position the read-write heads over theThe time required to position the read-write heads over the required track is the seek time.required track is the seek time.  The time required for the read-write head to come to aThe time required for the read-write head to come to a complete stop after it is moved is called the settling time.complete stop after it is moved is called the settling time.  The time required for the disk to rotate to the position whereThe time required for the disk to rotate to the position where the beginning of the desired block arrives at the read-writethe beginning of the desired block arrives at the read-write head is latency.head is latency.  Average Rotational delay (latency) = ½ revolutionAverage Rotational delay (latency) = ½ revolution  Track capacity = 72 x 512 = 36 KBTrack capacity = 72 x 512 = 36 KB  Cylinder capacity = 20 x 36 = 720 KBCylinder capacity = 20 x 36 = 720 KB  Disk capacity = 2048 x 720 = 1.44 GBDisk capacity = 2048 x 720 = 1.44 GB
  66. 66. 08/16/13 66 Hard Disk DriveHard Disk Drive
  67. 67. 08/16/13 67 Hard Disk Technology –Hard Disk Technology – RAID SystemsRAID Systems  Stands for Redundant Array of Independent (orStands for Redundant Array of Independent (or Inexpensive) Disk.Inexpensive) Disk.  Designed to improve the fault tolerance andDesigned to improve the fault tolerance and performance of computer storage systems.performance of computer storage systems.  The main purpose is to increase the reliability andThe main purpose is to increase the reliability and availability.availability. i.e. If one disk fails, still no data is lost.i.e. If one disk fails, still no data is lost.  RAID is an assembly of disk drives, known as diskRAID is an assembly of disk drives, known as disk array, that operates as one storage unit.array, that operates as one storage unit.
  68. 68. 08/16/13 68 RAID SystemsRAID Systems  RAID functions are:RAID functions are:  Immediate availability of data and, dependingImmediate availability of data and, depending on the RAID level, recovery of lost data.on the RAID level, recovery of lost data.  Redundancy of data at a chosen level.Redundancy of data at a chosen level.  Depending on the level of RAID, this method of dataDepending on the level of RAID, this method of data storage provides the data redundancy needed for astorage provides the data redundancy needed for a highly secure system, with additional benefit of fasterhighly secure system, with additional benefit of faster retrieval of data through multiple channel access.retrieval of data through multiple channel access.
  69. 69. 08/16/13 69 RAID SystemsRAID Systems  The array includes drives, controllers, enclosure,The array includes drives, controllers, enclosure, power supplies, fans, cables, etc. and software.power supplies, fans, cables, etc. and software.
  70. 70. 08/16/13 70 ModemsModems  A device used to provide remote connectivity over the Telephone lines.  For two modems to communicate, must share the same protocol.  Protocol :Protocol :  Determines how two entities will communicate.Determines how two entities will communicate.
  71. 71. 08/16/13 71 ModemsModems  Connection of informationConnection of information superhighway is by way of a modem.superhighway is by way of a modem.  This is connected to the serial port ofThis is connected to the serial port of the computer.the computer.  The faster modem, the less the time itThe faster modem, the less the time it will take to download files to thewill take to download files to the computer. If long distance telephonecomputer. If long distance telephone charges are involved higher speedcharges are involved higher speed modems can save cost as well time.modems can save cost as well time.  Modems with speeds as high as 56,000Modems with speeds as high as 56,000 baud are advisable.baud are advisable.
  72. 72. 08/16/13 72 ModemsModems  It converts digital data used by the computers intoIt converts digital data used by the computers into analog signals for transmission over the telephoneanalog signals for transmission over the telephone line & converts the analog signals back to digitalline & converts the analog signals back to digital data. (Modulator & Demodulator)data. (Modulator & Demodulator)  Three modulation methods are:Three modulation methods are:  Frequency-shift keying (FSK)Frequency-shift keying (FSK)  Phase-shift keying (PSK)Phase-shift keying (PSK)  Quadrature amplitude modulation (QAM)Quadrature amplitude modulation (QAM)

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