The computer

1
The computer

• Dr. Yan Liu
• Department of Biomedical, Industrial and Human
  Factors Engineering
• Wright State University

2
Elements of a Computer System

• Input Devices for Interactive Use
• Text entry traditional keyboard, phone text
  entry, speech, handwriting, etc
• Pointing mouse, touchpad, stylus, etc
• Virtual reality and 3D interaction devices data
  gloves, SpaceBall, etc.
• Output Display Devices
• Different types of screens mostly using some form
  of bitmap display
• Large displays and situated displays for shared
  and public use
• Digital paper, in conjunction with digital pens,
  can be used to create handwritten digital
  documents
• Devices in the Physical World
• Sensors for movement, temperature, bio-signs,
  etc.
• Devices with sound, smell, and/or haptic
  feedbacks

3
Elements of a Computer System

• Memory
• Short-term memory RAM (random access memory)
• Long-term memory disks
• Capacity limitations
• Access methods
• Processing
• Processing speed
• Networks

4
Alphanumeric Keyboards

• One of the most common text entry devices in use
  today
• QWERTY Keyboards
• QWERTY are the first six letters at the top row
  of alphabetical keys
• The layout of the digits and letters is generally
  fixed except a few variations in some nations
  keyboards
• e.g. French keyboards interchange both "Q" and
  "W" with "A" and "Z", and move "M" to the right
  of "L"
• Non-alphanumeric keys vary
• e.g. There is a difference between key
  assignments on British and American keyboards
• Above 2 and 3 on the UK keyboard are the and
  , respectively, whereas and are on the
  USA keyboard
• The placement of brackets, backslashes and such
  like vary
• Not optimal for typing
• The reason for such the layout can be traced back
  to the days of mechanical typewriters

5
French keyboard
US keyboard
UK keyboard
6
Alphanumeric Keyboards

• Dvorak Keyboard
• An alternative standard keyboard layout to
  QWERTY, patented in 1936 by August Dvorak and
  Willam Dealey
• Designed to address the problems of inefficiency
  and fatigue that characterized the QWERTY
  keyboard layout
• Speed improvement of 10 15
• Reduction in user fatigue due to the increased
  ergonomic layout of the keyboard
• Has failed to replace QWERTY standard
• Currently, all major operating systems (e.g.
  Apple OS X, Microsoft Windows, GNU/Linux) can
  ship the Dvorak keyboard layout in addition to
  the QWERTY layout

7
Alphanumeric Keyboards

• Dvorak Keyboard (Cont.)
• Ergonomics principles of the design
• It is easier to type letters alternating between
  hands
• For maximum speed and efficiency, the most common
  letters should be the easiest to type. This means
  that they should be on the home row, the center
  row of alphabetical letters on a keyboard, which
  is where the fingers rest and under the strongest
  fingers
• The least common letters should be on the bottom
  row, which is the hardest row to reach
• The right hand should do more of the typing,
  because most people are right-handed
• Stroking should generally move from the edges of
  the board to the middle. An observation of this
  principle is that, for many people, when tapping
  fingers on a table, it is easier going from
  little finger to index than vice versa

8
Dvorak Keyboard Layout
9
Alphanumeric Keyboards

• Chord Keyboards
• Significantly different from normal alphanumeric
  keyboards
• Only a few keys are used
• Allow users to enter characters or commands
  formed by pressing several keys together, like
  playing a chord on a piano
• Advantages
• Extremely compact and thus can be built into a
  device (e.g. a pocket-sized computer) that is too
  small to contain a normal sized keyboard
• A large number of combinations available from a
  small number of keys allows text or commands to
  be entered with one hand, leaving the other hand
  free to do something else
• Disadvantages
• Lack of familiarity
• Cannot be used by a "hunt and peck" method, so
  their use is restricted to applications where
  additional training can be justified
• Hunt and peck typing (or two-fingered typing) is
  a common form of typing, in which the typist must
  find and press each key individually

10

• 12 keys, so more than 4000 combinations are
  potentially possible
• User can set up key combinations as macros for
  longer strings of text

Twiddler2 Developed by Handykey Corp.
11
Phone Pad and T9 Entry

• Two Modes in Phone Pads
• Keys mean digits (when entering phone numbers)
• Keys mean letters (when typing SMS messages)
• Mapping digits to letters, using numeric keys
  with multiple presses
• e.g. hello 4433555pause555666 (Laborious?)
• Experienced mobile phone users make use of highly
  developed shorthand to reduce the number of
  keystrokes
• e.g. lrnt 2 txt usng shrt wds
• T9 Algorithm
• Type as if there were a single key for each
  letter
• Uses a large dictionary to guess the right word
• e.g. 3926753 becomes example as there is only
  one meaningful word with letters that match the
  series of numbers
• When there are ambiguities about the possible
  words, a series of options are presented for the
  user to choose from

Mobile phone keypad with typical mapping of
digits to letters
12
Handwriting Recognition

• Text can be input into the computer using a pen
  and a digesting tablet
• Intuitive and natural interaction
• Challenges and Problems
• Handwriting recognition device must capture
  stroke information as well as letter shapes in
  handwriting
• Letters within words are shaped and often drawn
  very differently depending on the actual word
• Individual differences in handwriting are
  enormous
• The speed of handwriting is much lower than of
  typing
• Handwriting entry would be most useful in
  situations where a keyboard-based approach has
  problems
• e.g. Pen-based systems are used for taking notes,
  jotting down and sketching ideas, as well as
  acting as a diary, address book and organizer

13
Speech Recognition

• A promising yet still limited area of text entry
• Most Successful When
• The system has been trained and tuned to the
  users voice
• Limited vocabulary of command words
• Limitations in Handling
• External noise interfering
• Imprecision of pronunciation
• Large vocabularies
• Different speakers
• Current Applications
• Telephone information systems, hands-occupied
  situations (especially in military), those
  suffering repetitive strain injury (RSI)

14
Positioning, Pointing, and Drawing

• Mouse
• Invented by Douglas Engelbart around 1964
• A very common and easy to use handheld pointing
  device
• Characteristics
• Usually 1 to 3 buttons on top
• Used for making a selection, indicating an
  option, or initiating drawing etc.
• Operates in a planar fashion, moving around the
  desk
• Indirect input device
• A transformation is required to map from
  horizontal movement of mouse to the vertical
  movement of the cursor on the screen
• Can cause hand-eye coordination problems for
  novice users

15
Positioning, Pointing, and Drawing

• Mouse (Cont.)
• Mechanical mouse
• A ball on underside of the mouse rotates as the
  mouse moves
• Ball turns vertical and horizontal wheels
  (encoders) inside the mouse
• Encoders interrupt optical beams to generate
  electrical signals as they turn
• Sensors send electrical signals to computer
• Optical mouse
• Uses a light-emitting diode (LED) and photodiodes
  to detect movement relative to the underlying
  surface
• May be used on a special grid-like pad or just on
  desk
• Less susceptible to dust and dirt
• Laser mouse
• Enter the mainstream market around 2004
• Uses a small infrared laser which increases the
  resolution of the image taken by the mouse
• About 20 times more sensitive to the surface
  features used for navigation compared to
  conventional optical mouse

16
Optical mouse using red LED to project light onto
the tracking surface
Mechanical mouse
Wireless laser mouse
17
Positioning, Pointing, and Drawing

• Touchpad
• Small touch sensitive tablet
• Around 2-3 square inches
• Used mainly in laptop computers but now can be
  obtained separately to replace the mouse on
  desktop computers
• Operated by stroking the users finger over its
  surfaces to move the cursor
• Substitute for a computer mouse
• May require several strokes to move the cursor
  across the screen
• Acceleration settings
• The ratio of pad distance to screen distance
  varies with the speed of finger movement
• Faster movement of the finger leads to longer
  distance of movement on the screen

18
Positioning, Pointing, and Drawing

• Trackball
• Consists of a ball housed in a socket containing
  sensors to detect rotation of the ball (like an
  upside-down mechanical mouse)
• The user rolls the ball with the thumb, fingers,
  or the palm of the hand to move the cursor
• Separate buttons are required for selection
• The size and feel of the trackball affords
  significant differences in the usability of the
  device
• Weight, rolling resistance, and texture all
  contribute to the overall effect
• Heavily used in video games where highly
  responsive behaviour, including being able to
  spin the ball, is ideal

Logitech TrackMan
19
Positioning, Pointing, and Drawing

• Joystick
• Consists of a small palm-sized base box with a
  handheld stick whose movement provides both a
  direction and a quantity that can be used to
  control cursor movement or other types of
  interfaces
• Usually provided with buttons for selection
• On top or on front like a trigger
• Often used for games
• Inexpensive, robust, and familiar to users

CH Products Flightstick Pro
20
Positioning, Pointing, and Drawing

• Joystick (Cont.)
• Absolute joystick
• Position of the joystick in the base corresponds
  to the position of the cursor on the screen
• Movement is the important characteristic
• Isometric joystick (velocity-controlled joystick)
• Pressure on the stick corresponds to the velocity
  of the cursor
• Force feedback joystick
• Allows users to feel force of magnitude and
  orientation
• Gives users a stronger sense of reality

21
Positioning, Pointing, and Drawing

• Touch-Sensitive Screen
• Detect the presence of finger or stylus on the
  screen
• Works by the finger interrupting matrix of light
  beams, capacitance changes or ultrasonic
  reflections
• Direct pointing device
• User indicates which item is required by pointing
  to it
• Advantages
• Very fast and requires no specialised pointer
• Good for menu selection
• Suitable for use in hostile environment
• No separate hardware to become damaged or
  destroyed by dirt
• Relatively intuitive to use
• A popular choice for a wide variety of
  applications
• e.g. Information kiosks, ATM, airline e-ticket
  terminals, retail and restaurant systems, etc.

22
Positioning, Pointing, and Drawing

• Touch-Sensitive Screen (Cont.)
• Disadvantages
• Finger can leave greasy marks on the screen
• Quite inaccurate
• Difficult to select small regions or perform
  accurate drawing (finger is a fairly blunt
  instrument!)
• Lifting the arm to point to a vertical screen can
  be tiring
• The screen has to be within about a meter of the
  user to be reached

23
Positioning, Pointing, and Drawing

• Stylus
• A small pen-like pointer to draw directly on
  screen
• Used on a touch-sensitive screen for more
  accurate positioning and avoiding greasy marks
• Particularly popular in PDA and is being used in
  some laptop computers
• Light Pen
• Older technology used in the same way as stylus
• Connected to the screen by a cable and uses light
  from the screen to detect location
• Advantages
• Very direct and intuitive to use
• Disadvantages
• Can be tiring to use on upright displays
• Obscure the screen

24
Display Devices

• Bitmap Display
• Made of vast numbers of dots or pixels (the
  smallest complete sample of an image) in a
  rectangular grid
• The pixels may be in black and white, grayscale,
  or full color
• Aspect ratio
• The ratio of the width to height of the display
• 43 for most screens, 169 for wide-screen TV
• Display resolution
• The number of distinct pixels in each dimension
  that can be displayed
• 1024768 (XGA, eXtended Graphic Array), 12801024
  (SXGA, Super eXtended Graphics Array), and
  16001200 resolution (UXGA, Ultra-eXtended) are
  the most common display resolutions

25
Display Devices

• Bitmap Display (Cont.)
• Color depth
• Describes the number of colors that can be
  displayed on a monitor's screen (usually in bit)
• Each of the three primary colors (red, blue and
  green) has a number of bits that describe its
  color depth
• e.g. In a true color (24-bit color) display,
  red, blue, and green each has 8 bits or 256
  shades (28)

26
Display Devices

• Display Techniques
• Cathode-ray tube (CRT)
• A stream of electrons is emitted from an electron
  gun, which is then focused and directed by
  magnetic fields. As the beam hits the
  phosphor-coated screen, the phosphor is excited
  by the electrons and glows
• Used in TVs and computer monitors

27
Display Devices

• Display Techniques (Cont.)
• Liquid crystal display (LCD)/flat panel display
• Uses two sheets of polarizing material with a
  liquid crystal solution between them. An electric
  current passed through the liquid causes the
  crystals to align so that light cannot pass
  through them. Each crystal, therefore, is like a
  shutter, either allowing light to pass through or
  blocking the light
• Used in PDAs, portables and notebooks, and
  increasingly on desktop computers and even for
  home TV

28
Display Devices

• Display Techniques (Cont.)
• Comparisons of CRT and LCD
• Resolution and Viewing Quality
• Resolution on a CRT is flexible
• The resolution on an LCD can be changed, but if
  it is run at a resolution other than its native
  resolution, its performance or quality will drop
• Both types of monitor provide bright and vibrant
  color display however, LCDs cannot display the
  maximum color range that a CRT can
• A CRT monitor can be viewed from almost any
  angle, but the view on a LCD changes as the user
  moves different angles and distances away from
  the monitor
• Viewable screen size
• The monitor size of a CRT screen is larger than
  the actual viewable area due to its bulky frame
• The monitor size of a LCD screen is the same
  as, or very close to, the actual viewable area

29
Display Devices

• Display Techniques (Cont.)
• Comparisons of CRT and LCD
• Physical size
• CRT monitors are big, bulky and heavy
• e.g. An average 17-inch CRT monitor could be
  upwards of 40 lbs
• LCD monitors are small, compact and lightweight
• e.g. An average 17-inch LCD monitor is about 15
  lbs
• Price
• LCD is more expensive than CRT as one-time
  purchase but may be cheaper in the long-run due
  to its longer lifespan and lower power
  consumption

30
Display Devices

• Large Displays
• Used for meetings, lectures, advertisement, etc
• Technology types
• Gas plasma to create large flat bitmap displays
• Behave like regular screens except they are big
  and usually have the HDTV (high definition
  television) wide screen format
• Video wall (when very large screen areas are
  required)
• Several small screens (CRT or LCD) are placed
  together
• Projected display
• CRT, LCD, or digital light processing (DLP)
  projectors
• Body of the presenter may obscure the screen
• Back-projected
• Semi-frosted glass screen projector behind
• The size of the image is limited by the depth of
  the projection room behind

31
Display Devices

• Situated Displays
• Displays that are embedded in an environment and
  adapt the content they display to changes in the
  environment
• Large (e.g. monitors at airports) or small (e.g.
  electronic sticky note)
• Can be interactive, using stylus or
  touch-sensitive screen

Notes read by the office owner using web interface
A small situated display (an electronic sticky
note) beside an office door
Handwritten note left using stylus
32
Special Device, Physical Controls, and Sensors

• Keyboards and screens of traditional computers
  are not appropriate or impossible in some
  situations
• e.g. Interactive TV, in-car navigation systems,
  personal entertainment, etc.
• May require special displays, sound, touch,
  and/or smell outputs, and dedicated controls and
  sensors
• Special Displays
• Some visual outputs can take the form of analog
  representations of numeric values
• e.g. Dials, gauges or lights to signify the
  system state or trend
• Head-up display
• Used mainly in aircraft
• Transparent display that presents data without
  obstructing the user's view
• Minimize information overload by centralizing
  critical flight data (e.g. speed, altitude,
  compass, etc.) within the pilot's field of vision

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The head-up display of Boeing F/A-18 Hornet (a
modern all-weather carrier-capable strike fighter
jet)
34
Special Device, Physical Controls, and Sensors

• Sound Output
• Beeps, bongs, clanks, whistles, and whirrs as
  sound outputs for various effects
• Provide important feedback in interactive systems
• Keyboards can be set to emit a click each time a
  key is pressed
• Telephone keypads sound different tones when
  different keys are pressed
• A noise occurring signifies that the key has been
  successfully pressed
• Actual tone provides some information about the
  particular key that was pressed
• Touch, Feel and Smell
• Touch and feeling are important in some
  situations
• e.g. The feel of an instrument moving through
  different tissue types in virtual surgery The
  sense of vibration when a car is about to go off
  the track in computer games
• Haptic device
• Gives people a sense of touch with computer
  generated environments
• e.g force feedback joystick, cyber gloves, etc.
• Texture, smell
• Current technology is very limited

35
Special Device, Physical Controls, and Sensors
36
Special Device, Physical Controls, and Sensors

• Physical Controls
• Appropriate feedbacks are important in physical
  controls
• Haptic feedback
• e.g. When you press a button or turn a dial,
  getting a right level of resistance gives you
  feedback that you are doing something
• Visual feedback
• e.g. An indicator light shows the device has been
  turned on
• Audio feedback
• e.g. A beep when you press a smooth button

37
Special Device, Physical Controls, and Sensors

• Environment and Bio- sensors
• Environment sensors
• e.g. car courtesy light, energy saving light,
  RFID security tags, GPS, pressure sensors, etc.
• Biosensors
• Sensors used to capture physiological signs
• e.g. body temperature, heart rate, galvanic skin
  response, blink rate, etc.

38
Memory

• Short-Term Memory Random Access Memory (RAM)
• Silicon chips used to held the most active
  information
• Random" means that any piece of data can be
  returned quickly and in a constant time,
  regardless of its physical location and whether
  or not it is related to the previous piece of
  data
• Used as main memory or primary storage
• Different forms of RAM differ in their precise
  access time, power consumption, and
  characteristics
• Typical access time in the order of 10
  nano-seconds
• Typical Access rate is around 100MB per second
• Typical storage in modern personal computers is
  256 MB 1GB
• Usually volatile
• Information is lost if power is turned off
• Small amount of non-volatile RAM exists in many
  computers
• Much more expensive and only used when necessary

39
Memory

• Long-Term Memory Disks
• Long-term storage of persistent information
• Magnetic disks
• Coated with magnetic material on which data is
  stored
• Data can be recorded and erased any number of
  times
• Types
• Floppy disk
• A 5¼-inch floppy typically can hold 360K or 1.2MB
• A 3½-inch floppy normally stores 720K, 1.2MB or
  1.44MB
• Hard disk
• Can store 20MB hundreds of GB
• Much faster than floppy disks (up to about 100
  times faster)
• Removable cartridge
• Hard disk enclosed in plastic or metal cartridges
  so that it can be removed like a floppy disk
• Nearly as capacious and fast as a hard disk and
  has the portability of a floppy disk
• Relatively expensive

40
Memory

• Long-Term Memory Disks
• Optic disks
• Storage medium from which data is read and to
  which it is written by lasers
• More robust than magnetic media
• Types
• CD-ROM
• The data is permanent, can be read any number of
  times, but cannot be modified
• Useful for published materials (e.g. online
  reference books, multimedia and software
  distribution)
• WORM (write-once, read-many)
• Data can be written to it only once after that,
  it behaves like a CD-ROM
• Useful for backups
• Erasable
• Data can be erased and rewritten, just as
  magnetic disks
• Useful temporary backup

41
Speed and Capacity

• Some Sizes (all uncompressed)
• The textbook (text only 320,000 words) 2MB
• The Bible 4.5 MB
• Scanned page (11x8 inches, 8-bit grayscale,
  1200dpi) 128MB
• Digital photo (24 mega pixels, 24-bit color)
  10 MB
• Problem
• RAM may not be big enough for running several
  programs simultaneously
• Virtual Memory
• Some programs in RAM that have not been used
  recently are copied onto hard disk, freeing up
  space in RAM to load new applications
• Paging unused bits of the programs out of RAM
  into the hard disk
• Swapping the entire programs into the hard disk
• Slows down the computer
• The read/write speed of a hard drive is much
  slower than that of RAM

42
Speed and Capacity

• Implication
• An interactive system designer should think
  carefully about where information is stored and
  when it is transferred
• e.g. Suppose a user wants to read a document
  online. Instead of loading in the entire document
  before letting the user continue, just enough is
  loaded for the first page to be displayed, and
  the rest is loaded during idle moments

43
Processing and Networks

• Factors that Limit the Speed of Interactive
  System
• Computation bound
• Complex computation takes time and thus can cause
  frustrating delays
• The system should be designed so that long delays
  are not in the middle of interaction
• For a very long process, try to give an estimate
  of the process duration before it starts and an
  indication of the stage that the process has
  reached during the process
• e.g. Having a counter or slowly filling bar on
  the screen that indicates the amount done
• Storage channel bound
• The speed of memory access can interfere with
  interactive performance
• It is possible to trade off memory against
  processing speed if there is plenty of raw
  computational power
• e.g. Compressed data takes less space to store
  and is faster to read in and out, but the process
  of compressing data before storage and
  decompressing when retrieved leads to increased
  processing time

44
Processing and Networks

• Factors that Limit the Speed of Interactive
  System (Cont.)
• Graphics bound
• The most common bottleneck for many modern
  interfaces
• Updating graphic displays can take tremendous
  time
• Helpful to add a special-purpose graphics card
  (as a co-processor) optimised to take on the
  burden and allow the main processor to do other
  work
• Network capacity
• Many computers are linked through networks
• Interactive performance can be reduced by slow
  network speed

45
Processing and Networks

• Networked Computing
• Benefits
• Increased computing power and memory
• Communication with other people through
  groupwares (e.g. emails and instant messages)
• Shared resources
• Issues
• Slow feedbacks due to network delays
• Slower response when many people access the same
  information at the same time
• Unpredictability of system performance because an
  individual is unaware of many important things
  that are happening to the system as a whole