Input and Output

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					Input Devices - Keyboard
 Similar to a typewriter keyboard
   alphanumeric keys
   tab, shift, capslock, enter
   numeric keypad
   function keys
   special keys: escape, control, alternate
 can be designed for various languages
    Chinese keyboard (which input method?)
 on applications
    fast food (keys correspond not to characters but products, or functions
     such as taxes)
 ergonomic keyboards
Mice and the like

As user moves mouse
a ball under the mouse rolls on a flat surface,
 the movements of the ball are translated into
 movements of the cursor
connected to the computer’s bus
  through a mouse socket to a circuit board (“card”)
  through a serial port (a socket) to which user can
   connect external devices such as mouse or modem
point, click, double-click, drag
Track Ball
  An upside-down mouse
  user rolls the ball directly
  requires less space

Optical Mouse
  a photo-detector senses the mouse’s movement
   over a special pad with gridlines printed on it
Touch Screens

Sensors in or near the computer’s screen
that can detect the touch of a finger
easy to use
not suitable for complicated input
Bar Code Readers

 a laser beam scans patterns of printed bars
 and converts them into numerical digits
faster and more accurate than manual input

 use an electric pen to point and write
on a special pad or the screen
used in personal digital assistants
Chinese hard writing input
not good for large amounts of text

 converts image into a digitized form - a bit
shines light onto an image and measures
 intensity of the reflection at every point
optical character recognition (off-line
 recognition is harder)
Voice Input

 speech recognition
converts sound waves into electrical
 waveform into binary code
speaker dependent
discrete word systems - user must pause
 between words
continuous word systems are much more
Output devices - The Monitor
 the typical monitor users a cathode ray tube (CRT)
 an electron gun systematically aims at every phosphor dot on
  the screen to reproduce an image - a pixel grows
 the brightest and clearest for the money
 a monochrome tube has only one beam
 a color monitor has 3 beams (red, green, blue)
 horizontal and vertical resolutions (e.g., 800x600, 1024x768,
 flicker appears when a monitor scans too slowly
 refresh rate = the number of times the monitor repaints the
  entire screen each second (e.g., 60 Hz , 75 Hz)
 notebooks typically use liquid crystal displays
a liquid crystal that is normally transparent,
 but turns opaque when charged with electricity
require less power
lower contrast (does not emit light)
can be improved with back-lighting
The Video Controller
 goes between the monitor and the CPU
 contains the memory an other circuitry necessary to send
  information from the CPU to the monitor
 dual port memory allows data to be stored into the memory
  from the CPU while the controller sends the data to the
 text mode
   80 columns x 25 rows of cahracters
   2 bytes per character position
   controller reads the byte that specifies the character and displays the
    dot pattern
   cannot display complex graphics
 graphics mode
   all points addressable
   amount of memory required per pixel depends on number
    of color that can be displayed by the monitor
   generations of graphics modes
      Color Graphics Adaptor (CGA)
      Enhanced Graphics Adaptor (EGA)
      Video Graphics Adaptor (VGA) 640x480
      Super VGA (SVGA) 800x600
      Extended Graphics Array (XGA) 1024x768

Dot Matrix
 first printers used with PCs
 pins on a print head strike the paper through an inked ribbon
  to create an image
 from 9 pins to 24 pins
 have text modes and graphics modes
 low image quality, slower, and noisier
 cheaper
 suitable for multi-copy forms
Ink Jet
   spray ink directly on paper through up to 64 nozzles
   quiet, not very fast

   laser writes on a +ve charged drum
   charge neutralized where laser writes
   toner sticks to neutral spots
   toner transferred to paper from drum

 a robotic arm draws with colored pens
for large drawings or images
Voice Output

 speech synthesis is easier than speech recognition
 voice synthesizers convert data into vocalized sounds
 synthesis by analysis -
   analyze the human voice input
   store the spoken sounds
   reproduce the sound when needed
   more natural, but limited to the number of words stored
 synthesis by rule
   apply linguistic rules to create artificial speech
Other Outputs

Computer Graphics
Virtual Reality
Secondary Storage

Separate from the computer
necessary because memory is not permanent
 and limited in size
Magnetic Disk

 Diskettes, hard disks, and tape are magnetic
 The surfaces are coated with iron particles
 Each bit is stored on a magnetized spot on the disk:
  magnetized: 1; otherwise: 0
 The surface of each disk has concentric tracks of spots
 to write:electromagnets on read/write heads
  magnetize/demagnetize the iron particles
 to read: the presence/absence of magnetism in the spot is
  detected by the read/write head
 the disk drive is a device that reads/writes to the disk
Hard Disk

A metal coated with magnetic oxide
several disks can be assembled into a disk pack
a disk drive is a machine that can read/write on a
 disk, a disk pack is mounted on a disk drive,
 separate from the computer
all disks in a disk pack rotate together, although
 only one disk is being read/write at one time
If the head touches the surface, it is a head
 crash and data may be destroyed
a disk pack has a stack of access arms which
 slips between the disks
most disk packs combine the disks, arms, and
 heads in a sealed module called a Winchester
Optical disks

The surface of the disk is coated with a
 metallic material
a laser makes tiny spots on the surfaces,
 altering the way light is reflected
cheap, compact, high-capacity
read-only - recorded by the manufacturer
write once, read-many (WORM)

Compact disk, read only memory
format identical to audio CDs - plants making
 audio CDs can easily produce CR-ROMs to
 distribute software
up to 660 megabytes ~= 400 3-1/2 inch
there are now also record able CD-ROMs

floppy disks spin at ~300 RPM
easy back up
convenient software distribution
holds 1.4 MB

A record able CD-ROM technology using a disc that
 can be written only once
the discs can be read on any CD-ROM reader
To record a full 650MB disc takes from 20 minutes
 to an hour depending on the speed of the drive
large numbers of CD-ROMs are duplicated on a
 pressing machine from a master plate derived from
 the original CD-R recording
Drive Performance

Average access time (to position the head)
     floppy disk ~200 milliseconds
     hard disk ~15 milliseconds
     CD-ROM ~100 milliseconds

data transfer rate
  MB per second
Magnetic Tapes

Looks like audio tapes
data is stored linearly, and measured in terms
 of density:characters per inch or bytes per inch
digital audio tape (DAT) uses helical scan
usually used as back up
Back up
Data in a computer may be corrupted by head crashes
 in the hard disk, other hardware errors, software
 errors, and human errors.
Hence it is prudent to store data in more than one
 place to protect it from damage or errors
large organizations usually back up on magnetic tape
PC users may back up onto diskettes
now Zip disks offer an alternative
  100MB capacity

DVD stands for digital video disk
A DVD-ROM can store from 4.7 GB(more
 than seven times that of a CD-ROM) to 17 GB
Such storage capacity is needed for files
 containing both text, audio, graphics, and
 video- in other words, multimedia.
Small Computer System Interface (SCSI)

 Originally designed to connect 3rd party peripheral devices to
  IBM mainframes
 popular, used on all sorts of computers
 all circuitry on the drive itself
 connects the drive to the system bus itself
 high transfer rates
 can be considered an extension of the system bus
 several devices can be connected in a chain to a single SCSI

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