2ND QUIZ

• The Computer - a computer system is made up of various elements
• A ‘typical’ computer system -

  • screen, or monitor, on which there are windows​
  • keyboard​
  • mouse/trackpad
• Keyboards - Most common text input device
• QWERTY - Standardised layout
• Alphabetic​ - keys arranged in alphabetic order
• Dvorak​ - common letters under dominant fingers
• special keyboards - designs to reduce fatigue for Repetitive Strain Injury
• Chord keyboards - only a few keys - four or 5​

  letters typed as combination of keypresses
• phone pad - use numeric keys with​multiple presses
• T9 predictive entry​ - type as if single key for each letter
• Handwriting recognition - Text can be input into the computer, using a pen and a digesting tablet
• Speech recognition - Improving rapidly and Most successful when:​

  • single user – initial training and learns peculiarities
• Numeric keypads - for entering numbers quickly:​

  • calculator, PC keyboard
• the Mouse - Handheld pointing device​

  • very common​
  • easy to use
• Two methods for detecting motion

  • Mechanical
  • Optical
• Mechanical​ - Ball on underside of mouse turns as mouse is moved
• Optical​ - light emitting diode on underside of mouse
• footmouse​ - controlling mouse movement with feet
• Touchpad - small touch sensitive tablets
• A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes
• Joystick​

  • Indirect​pressure of stick = velocity of movement ​
  • buttons for selection​on top or on front like a trigger​
  • often used for computer games​aircraft controls and 3D navigation
• Keyboard nipple​

  • for laptop computers​
  • miniature joystick in the middle of the keyboard
• Touch-sensitive screen - Detect the presence of finger or stylus on the screen.
• Stylus​

  • small pen-like pointer to draw directly on screen
• Light Pen​

  • now rarely used​
  • uses light from screen to detect location
• Digitizing tablet - Mouse like-device with cross hairs
• Eyegaze

  • control interface by eye gaze direction​
  • e.g. look at a menu item to select it
• Cursor keys - Four keys (up, down, left, right) on keyboard.
• Discrete positioning controls - in phones, TV controls etc.​

  • cursor pads or mini-joysticks​
  • discrete left-right, up-down​
  • mainly for menu selection
• bitmap displays - Virtually all computer displays are based on some sort of bitmap
• Jaggies​

  • diagonal lines that have discontinuities in due to horizontal raster scan process.
• Anti-aliasing​

  • softens edges by using shades of line colour​
  • also used for text
• Resolution - used (inconsistently) for number of pixels on screen (width x height)

  • e.g. SVGA 1024 x 768, PDA perhaps 240x400
• Aspect ratio

  • ratio between width and height
• Colour depth:

  • how many different colours for each pixel?
• Cathode ray tube - Stream of electrons emitted from electron gun, focused and directed by magnetic fields, hit phosphor-coated screen which glows
• Liquid crystal displays (LCD) - Smaller, lighter, and … no radiation problems.
• Direct view storage tube (DVST)​

  • Similar to random scan but persistent => no flicker
• Random Scan (Directed-beam refresh, vector display)​

  • draw  the lines to be displayed directly
• large displays - used for meetings, lectures, etc.