Input and Output

Input and Output (I/O) devices translate things people can understand into 
things machines can understand and visa versa.

A. Input devices: keyboard vs. direct

   1. Keyboard entry devices
      - input comes by typing a 'source document' into the computer
   2. Direct entry devices
      - input comes in directly in machine-readable form, no keyboard
   3. Example
      - POS terminals may use both types of data entry, a keyboard
        to enter prices or a wand reader or platform scanner to record 
        special characters on price tags

B. Keyboard input devices

   1. Keyboards (QWERTY vs. Dvorak)
      a. Typewriter keys (note: Return and Enter keys are the same)
      b. Function keys
      c. Numeric keys (useful for spreadsheets)
      d. Special-purpose keys (Esc, Ctrl, Del, Ins, arrow keys)
   2. Terminals

C. Direct Entry

   1. Pointing devices
      a. mouse (types - trackball, finger mouse, optical mouse, etc.)
      b. touch screen
      c. light pen (connection closed when touching monitor)
      d. digitizer (used to trace or copy objects, digitizing tablets)
      e. pen-based computing (Newton, PDAs)
   2. Scanning devices
      a. Image scanners (flatbed or handheld, OCR software)
      b. Fax machines/fax boards/fax modems
      c. Bar code readers (read UPC symbols)
      d. character and mark recognition devices
         i. magnetic ink character recognition (MICR) - bank checks
         ii. optical character recognition (OCR)
         iii. optical mark recognition (OMR) - exam grading machines
   3. Voice input devices

D. Output devices

   1. Types of monitors
      a. Key terms
         i. monitor/ display screen/ VDT are synonymous
         ii. screen resolution (clarity of images on a screen)
         iii. pixels - dots used to form pictures (density and clarity
            related, the more pixels the higher resolution of the 
      b. Screen types
         i. CRTs - Cathode Ray Tubes (same as a television set)
         ii. flat panel displays - for portable computers
      c. Monochrome monitors
         i. rare on personal computers today
         ii. on portables because they consume less energy than color
         iii. Liquid Crystal Displays (LCDs) 
            - electric field causes molecules to line up, 
            - difficult to read in light, may require backlighting
         iv. Electroluminescent displays (EL) - LCD that actively 
            emits light
      d. color monitors
         i. passive and active panels (active gives best results)
         ii. Adapters boards
            - CGA (4 colors, 320x200 resolution)
            - EGA (Enhanced GA) - 16 colors, 640x350)
            - VGA (Video Graphics Array) 
                16 colors, 640x480 OR 256 colors, 320x200)
            - Super VGA (800x600 up to 1024x768)
            - XGA (Extended Graphics Array) - 256+ colors, 1024x768
              capable of up to 65,536 colors when specially equipped
   2. Printers
      a. Dot matrix
         i. inexpensive
         ii. most popular printers out there
         iii. constructs characters with dots (9, 18, 24 pin heads)
         iv. often noisy
         v. paper feed problems a constant annoyance
      b. Laser printers
         i. constructs dot-like images (300 dpi, 600 dpi, etc.)
         ii. excellent quality output
         iii. popular for dtp
         iv. technology similar to a photocopy machine (toner is 
            magnetically charged and transferred from drum to 
            paper by heat process
         v. 8 pages per minute common
         vi. more expensive with Postscript capability
      c. Ink-Jet Printer
         i. sprays small dropt of ink onto paper
         ii. can easily be used for color
         iii. increasing in popularity
      d. Thermal printers
         i. heat element produces an image on heat-sensitive paper
         ii. color versions are expensive
      e. misc. impact printers
         i. daisywheel printers
         ii. line printers (mainframe environments with 
            high output volume needs)
      f. general comments about printers
         i. bidirectional is best for character (vs. page) printers
         ii. friction and tractor feeds (align paper correctly)
         iii. type styles (hardware fix on some, software on others)
         iv. portable printers are most often ink-jet or bubble-jet
   3. Plotters
   4. Voice output devices