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					Chapter 10
Computer Peripherals
 The Architecture of Computer Hardware
        and Systems Software:
    An Information Technology Approach
          3rd Edition, Irv Englander
         John Wiley and Sons 2003
Peripherals
  Devices that are separate from the
   basic computer
        Not the CPU, memory, power supply
  Classified as input, output, and storage
  Connect via
        Ports
               parallel, USB, serial
        Interface to systems bus
               SCSI, IDE, PCMCIA

Chapter 10 Computer Peripherals              10-2
Storage Devices
  Primary memory
  Expanded storage
  Secondary storage
        Data and programs must be copied to
         primary memory for CPU access
        Permanence of data
        Direct access storage devices (DASDs)
        Online storage
        Offline storage – loaded when needed

Chapter 10 Computer Peripherals                  10-3
Speed
  Measured by access time and data
   transfer rate
  Access time: average time it takes a
   computer to locate data and read it
        millisecond = one-thousandth of a second
  Data transfer rate: amount of data that
   moves per second


Chapter 10 Computer Peripherals                 10-4
Hierarchy of Storage
Device                             Typical Access Times     Throughput Rate
CPU Registers
Cache Memory (SRAM)                 15 to 30 nanoseconds
Conventional Memory (DRAM)         50 to 100 nanoseconds
Expanded Storage (RAM)             75 to 500 nanoseconds

Hard Disk Drive                     10 to 50 milliseconds   600 to 6,000 KB/sec
Floppy Disk                              95 milliseconds    100 to 200 KB/sec
CD-ROM                            100 to 600 milliseconds   500 to 4,000 KB/sec
Tape                              .5 and up seconds         2,000 KB/sec   (cartridge)


Chapter 10 Computer Peripherals                                                10-5
Secondary Storage Devices
    Hard drives, floppy drives
    CD-ROM and DVD-ROM drives
    CD-R, CD-RW, DVD-RAM, DVD-RW
    Tape drives
    Network drives
    Direct access vs. Sequential access
    Rotation vs. Linear

Chapter 10 Computer Peripherals            10-6
Magnetic Disks
    Track – circle
    Cylinder – same track on all platters
    Block – small arc of a track
    Sector – pie-shaped part of a platter
    Head – reads data off the disk

  Head crash
  Parked heads
  Number of bits on each track is the same! Denser towards the
   center.
  CAV – constant angular velocity
        Spins the same speed for every track
        Hard drives – 3600 rpm – 7200 rpm
        Floppy drives – 360 rpm

Chapter 10 Computer Peripherals                              10-7
A Hard Disk Layout




Chapter 10 Computer Peripherals   10-8
Locating a Block of Data
  Average seek time: time
   required to move from one track
   to another


  Latency: time required for disk to
   rotate to beginning of correct
   sector


  Transfer time: time required to
   transfer a block of data to the
   disk controller buffer
Chapter 10 Computer Peripherals         10-9
Disk Access Times
  Avg. Seek time
        average time to move from one track to another
  Avg. Latency time
        average time to rotate to the beginning of the
         sector
        Avg. Latency time = ½ * 1/rotational speed
  Transfer time
        1/(# of sectors * rotational speed)
  Total Time to access a disk block
        Avg. seek time + avg. latency time + avg. transfer time

Chapter 10 Computer Peripherals                                    10-10
Magnetic Disks
  Data Block Format
          Interblock gap           Disk Interleaving

          Header
          Data
          Formatting disk
  Disk Interleaving
  Disk Arrays
        RAID – mirrored, striped
        Majority logic  fault-tolerant computers
Chapter 10 Computer Peripherals                         10-11
Disk Block Formats
                                  Single Data Block




                            Header for Windows disk




Chapter 10 Computer Peripherals                       10-12
Alternate Disk Technologies
  Removable hard drives
        Disk pack – disk platters are stored in a plastic case that is
         removable
        Another version includes the disk head and arm assembly in
         the case
  Fixed-head disk drives
        One head per track
        Eliminates the seek time
  Bernoulli Disk Drives
        Hybrid approach that incorporates both floppy and hard disk
         technology
        Zip drives

Chapter 10 Computer Peripherals                                    10-13
Magnetic Tape
    Offline storage
    Archival purposes
    Disaster recovery
    Tape Cartridges
          20 – 144 tracks (side by side)
          Read serially (tape backs up)
          QIC – quarter inch cartridge (larger size)
          DAT – digital audio tape (small size)
          Size typically includes (2:1 compression)
Chapter 10 Computer Peripherals                     10-14
Optical Storage
  Reflected light off a mirrored or pitted surface
  CD-ROM
        Spiral 3 miles long, containing 15 billion bits!
        CLV – all blocks are same physical length
        Block – 2352 bytes
               2k of data (2048 bytes)
               16 bytes for header (12 start, 4 id)
               288 bytes for advanced error control
  DVD-ROM
        4.7G per layer
        Max 2 layers per side, 2 sides = 17G

Chapter 10 Computer Peripherals                             10-15
Optical Storage
  Laser strikes land: light reflected into detector
  Laser strikes a pit: light scattered




Chapter 10 Computer Peripherals                 10-16
Layout: CD-ROM vs. Standard Disk

             CD-ROM               Hard Disk




Chapter 10 Computer Peripherals               10-17
CD-ROMs
                                    Seek Time
        General Speed             (milliseconds)      Data Transfer Rate
          Single-Speed                 600         150K per second

                 2X                    320         300K per second

                 3X                    250         450K per second

                 4X                  135-180       600K per second

                 6X                  135-180       900K per second

                 8X                  135-180       1.2 MBps
                10X                  135-180       1.6 MBps

                12X                  100-150       1.8 MBps

                16X                  100-150       2.4 MBps (maximum)

                24X                  100-150       3.6 Mbps (maximum)

                32X                  100-150       4.8 Mbps (maximum)
Chapter 10 Computer Peripherals                                            10-18
Types of Optical Storage
  WORM Disks
        Write-once-read-many times
        Medium can be altered by using a medium-powered laser to
         blister the surface
        Data stored in concentric tracks, sectored like a magnetic
         disk
        CAV
  Medium-powered laser blister technology also used
   for
        CD-R, DVD-R, DVD-ROM
        CD-RW, DVD-RW, DVD-RAM, DVD+RAM
  Magneto-Optical Disks
Chapter 10 Computer Peripherals                                 10-19
Displays
  Pixel – picture element
  Size: diagonal length of screen
  Resolution (pixels on screen)
     VGA: 480 x 640
     SVGA: 600 x 800
     768 x 1024
     1280 x 1024
  Picture size calculation
     Resolution * bits required to represent number of
      colors in picture
     Example: 16 color image, 100 pixels by 50 pixels
      4 bits (16 colors) * 100 * 50 = 20,000 bits

Chapter 10 Computer Peripherals                           10-20
Display Screen
 Screen size: measured
  diagonally
 Resolution: minimum
  identifiable pixel size
 Aspect ratio: x pixels to
  y pixels
       4:3 on most PCs
       16:9 on high definition
        displays



Chapter 10 Computer Peripherals   10-21
Color and Displays
  Pixel color is determined by intensity of
   3 colors – Red Green Blue or RGB
  4 bits per color
        16 x 16 x 16 = 4096 colors
  24 bit color (True Color)
        16.7 million colors
  Video memory requirements are
   significant!
Chapter 10 Computer Peripherals           10-22
CRT’s and Text Monitors
  CRTs (similar to TVs)
          3 stripes of phosphors for each color
          3 separate electron guns for each color
          Strength of beam  brightness of color
          Raster scan
               30x per second
               Interlaced vs. non-interlaced (progressive scan)
  Text monitors
          24 lines x 80 chars
          A character is the smallest unit on a screen
          Very little memory required
          Fast for remote transmissions

Chapter 10 Computer Peripherals                                    10-23
Interlaced vs Noninterlaced




Chapter 10 Computer Peripherals   10-24
Diagram of Raster Screen
Generation Process




Chapter 10 Computer Peripherals   10-25
Display Example




Chapter 10 Computer Peripherals   10-26
LCD – Liquid Crystal Display
  Fluorescent light panel
  3 color cells per pixel
  Operation
        1st filter polarizes light in a specific direction
        Electric charge rotates molecules in liquid crystal
         cells proportional to the strength of colors
        Color filters only let through red, green, and blue
         light
        Final filter lets through the brightness of light
         proportional to the polarization twist

Chapter 10 Computer Peripherals                           10-27
LCD Operation




Chapter 10 Computer Peripherals   10-28
LCDs (continued)
  Active matrix
        One transistor per cell
        More expensive
        Brighter picture
  Passive matrix
        One transistor per row or column
        Each cell is lit in succession
        Display is dimmer since pixels are lit less
         frequently

Chapter 10 Computer Peripherals                    10-29
Printers
  Dots vs. pixels
        300-2400 dpi vs. 70-100 pixels per inch
        Dots are on or off, pixels have intensities
  Types
          Typewriter / Daisy wheels – obsolete
          Dot matrix – usually 24 pins, impact printing
          Inkjet – squirts heated droplets of ink
          Laserjet
          Thermal wax transfer
          Dye Sublimation

Chapter 10 Computer Peripherals                            10-30
Creating a Gray Scale




Chapter 10 Computer Peripherals   10-31
Laser Printer Operation
1. Dots of laser light are beamed onto a drum
2. Drum becomes electrically charged
3. Drum passes through toner which then sticks to
   the electrically charged places
4. Electrically charged paper is fed toward the
   drum
5. Toner is transferred from the drum to the paper
6. The fusing system heats and melts the toner
   onto the paper
7. A corona wire resets the electrical charge on
   the drum
Chapter 10 Computer Peripherals                 10-32
Laser Printer Operation




Chapter 10 Computer Peripherals   10-33
Laser Printer Operation




Chapter 10 Computer Peripherals   10-34
Other Computer Peripherals
  Scanners
        Flatbed, sheet-fed, hand-held
        Light is reflected off the sheet of paper
  User Input Devices
        Keyboard, mouse, light pens, graphics
         tablets
  Communication Devices
        Telephone modems
        Network devices

Chapter 10 Computer Peripherals                      10-35

				
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