CHAPTER 2 Flashcards
1
Q
a computer system is made up of various elements
A
The Computer
2
Q
text entry and pointing
A
input devices
3
Q
screen (small&large), digital paper
A
output devices
4
Q
special interaction and display devices
A
virtual reality
5
Q
e.g. sound, haptic, bio-sensing
A
physical interaction
6
Q
as output (print) and input (scan)
A
paper
7
Q
RAM & permanent media, capacity & access
A
memory
8
Q
speed of processing, networks
A
processing
9
Q
to understand human–computer interaction
… need to understand computers!
A
Interacting with computers
10
Q
screen, or monitor, on which there are windows
keyboard
mouse/trackpad
A
typical
11
Q
variations of typical computer system
A
– desktop
– laptop
– PDA
12
Q
How many computers in your house?
A
PC
– TV, VCR, DVD, HiFi,
cable/satellite TV
– microwave, cooker,
washing machine
– central heating
13
Q
How many computers in your pockets?
A
– PDA
– phone, camera
– smart card, card with
magnetic strip?
– electronic car key
– USB memory
try your pock
14
Q
keyboards (QWERTY et al.)
chord keyboards, phone pads
handwriting, speech
A
text entry devices
15
Q
Most common text input device
• Allows rapid entry of text by experienced
users
• Keypress closes connection, causing a
character code to be sent
• Usually connected by cable, but can be
wireless
A
Keyboards
16
Q
Standardised layout
but …
– non-alphanumeric keys are placed differently
– accented symbols needed for different scripts
– minor differences between UK and USA keyboards
A
layout – QWERTY
17
Q
alternative keyboard layouts
A
Alphabetic and Dvorak
18
Q
keys arranged in alphabetic order
– not faster for trained typists
– not faster for beginners either!
A
Alphabetic
19
Q
common letters under dominant fingers
– biased towards right hand
– common combinations of letters alternate between hands
– 10-15% improvement in speed and reduction in fatigue
– But - large social base of QWERTY typists produce market
pressures not to change
A
Dvorak
20
Q
designs to reduce fatigue for RSI
• for one handed use
e.g. the Maltron left-handed keyboard
A
special keyboards
21
Q
only a few keys - four or 5
letters typed as combination of keypresses
compact size
– ideal for portable applications
short learning time
– keypresses reflect letter shape
fast
– once you have trained
BUT - social resistance, plus fatigue after extended use
NEW – niche market for some wearables
A
Chord keyboards
22
Q
use numeric keys with
multiple presses
2 – a b c 6 - m n o
3 - d e f 7 - p q r s
4 - g h i 8 - t u v
5 - j k l 9 - w x y z
hello = 4433555[pause]
A
phone pad
23
Q
type as if single key for each letter
– use dictionary to ‘guess’ the right word
– hello = 43556 …
– but 26 -> menu ‘am’ or ‘an
A
T9 entry
24
Q
Text can be input into the computer, using a
pen and a digesting tablet
– natural interaction
• Technical problems:
– capturing all useful information - stroke path,
pressure, etc. in a natural manner
– segmenting joined up writing into individual letters
– interpreting individual letters
– coping with different styles of handwriting
• Used in PDAs, and tablet computers …
… leave the keyboard on the desk!
A
Handwriting recognition
25
Improving rapidly
• Most successful when:
– single user – initial training and learns peculiarities
– limited vocabulary systems
• Problems with
– external noise interfering
– imprecision of pronunciation
– large vocabularies
– different speakers
Speech recognition
26
for entering numbers quickly:
– calculator, PC keyboard
• for telephones
Numeric keypads
27
Handheld pointing device
– very common
– easy to use
• Two characteristics
– planar movement
– buttons
(usually from 1 to 3 buttons on top, used for
making a selection, indicating an option, or to
initiate drawing etc.
the Mouse
28
Two methods for detecting motion
Mechanical
Optical
29
Ball on underside of mouse turns as mouse is moved
– Rotates orthogonal potentiometers
– Can be used on almost any flat surface
Mechanical
30
light emitting diode on underside of mouse
– may use special grid-like pad or just on desk
– less susceptible to dust and dirt
– detects fluctuating alterations in reflected light intensity to
calculate relative motion in (x, z) plane
Optical
31
small touch sensitive tablets
• ‘stroke’ to move mouse pointer
• used mainly in laptop computers
• good ‘acceleration’ settings important
– fast stroke
• lots of pixels per inch moved
• initial movement to the target
– slow stroke
• less pixels per inch
• for accurate positioning
Touchpad
32
ball is rotated inside static housing
• like an upsdie down mouse!
– relative motion moves cursor
– indirect device, fairly accurate
– separate buttons for picking
– very fast for gaming
– used in some portable and notebook computers.
Trackball
33
for accurate CAD – two dials for X-Y cursor position
– for fast scrolling – single dial on mouse
Thumbwheels
34
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
Joystick
35
for laptop computers
– miniature joystick in the middle of the keyboard
Keyboard nipple
36
works by interrupting matrix of light beams, capacitance changes
or ultrasonic reflections
– direct pointing device
Detect the presence of finger or stylus on the screen
37
fast, and requires no specialised pointer
– good for menu selection
– suitable for use in hostile environment: clean and safe from
damage.
Advantages
38
finger can mark screen
– imprecise (finger is a fairly blunt instrument!)
• difficult to select small regions or perform accurate drawing
– lifting arm can be tiring
Disadvantages
39
small pen-like pointer to draw directly on screen
– may use touch sensitive surface or magnetic detection
– used in PDA, tablets PCs and drawing tables
Stylus
40
– now rarely used
– uses light from screen to detect location
Light Pen
41
very direct and obvious to use
– but can obscure screen
BOTH
42
Mouse like-device with cross hairs
• used on special surface
- rather like stylus
• very accurate
- used for digitizing maps
Digitizing tablet
43
control interface by eye gaze direction
– e.g. look at a menu item to select it
• uses laser beam reflected off retina
– … a very low power laser!
• mainly used for evaluation (ch x)
• potential for hands-free control
• high accuracy requires headset
• cheaper and lower accuracy devices available
sit under the screen like a small webcam
Eyegaze
44
Four keys (up, down, left, right) on keyboard.
• Very, very cheap, but slow.
• Useful for not much more than basic motion for textediting tasks.
• No standardised layout, but inverted “T”, most common
Cursor keys
45
cursor pads or mini-joysticks
– discrete left-right, up-down
– mainly for menu selection
in phones, TV controls etc.
46
bitmap screens (CRT & LCD)
large & situated displays
digital paper
display devices
47
screen is vast number of coloured dots
bitmap displays
48
number of pixels on screen (width x height)
• e.g. SVGA 1024 x 768, PDA perhaps 240x400
– density of pixels (in pixels or dots per inch - dpi)
• typically between 72 and 96 dpi
Resolution … used (inconsistently) for
49
ration between width and height
– 4:3 for most screens, 16:9 for wide-screen TV
Aspect ratio
50
how many different colours for each pixel?
– black/white or greys only
– 256 from a pallete
– 8 bits each for red/green/blue = millions of colours
Colour depth:
51
diagonal lines that have discontinuities in due to horizontal
raster scan process.
Jaggies
52
softens edges by using shades of line colour
– also used for text
Anti-aliasing
53
Stream of electrons emitted from electron gun, focused
and directed by magnetic fields, hit phosphor-coated
screen which glows
• used in TVs and computer monitors
electron gun
focussing and
deflection
Cathode ray tube
54
• X-rays: largely absorbed by screen (but not at rear!)
• UV- and IR-radiation from phosphors: insignificant
levels
• Radio frequency emissions, plus ultrasound (~16kHz)
• Electrostatic field - leaks out through tube to user.
Intensity dependant on distance and humidity. Can
cause rashes.
• Electromagnetic fields (50Hz-0.5MHz). Create induction
currents in conductive materials, including the human
body. Two types of effects attributed to this: visual
system - high incidence of cataracts in VDU operators,
and concern over reproductive disorders (miscarriages
and birth defects)
Health hazards of CRT !
55
Smaller, lighter, and … no radiation problems.
• Found on PDAs, portables and notebooks,
… and increasingly on desktop and even for home TV
• also used in dedicted displays:
digital watches, mobile phones, HiFi controls
• How it works …
– Top plate transparent and polarised, bottom plate reflecting.
– Light passes through top plate and crystal, and reflects back to
eye.
– Voltage applied to crystal changes polarisation and hence colour
– N.B. light reflected not emitted => less eye strain
Liquid crystal displays
56
special displays
Random Scan (Directed-beam refresh, vector display)
Direct view storage tube (DVST)
57
draw the lines to be displayed directly
– no jaggies
– lines need to be constantly redrawn
– rarely used except in special instruments
Random Scan
58
Similar to random scan but persistent => no flicker
– Can be incrementally updated but not selectively erased
– Used in analogue storage oscilloscopes
(DVST)
Direct view storage tube (DVST)
59
used for meetings, lectures, etc.
• technology
plasma – usually wide screen
video walls – lots of small screens together
projected – RGB lights or LCD projector
– hand/body obscures screen
– may be solved by 2 projectors + clever software
back-projected
– frosted glass + projector behind
large displays
60
displays in ‘public’ places
– large or small
– very public or for small group
• display only
– for information relevant to location
• or interactive
– use stylus, touch sensitive screem
• in all cases … the location matters
– meaning of information or interaction is related to
the location
situated displays
61
what?
– thin flexible sheets
– updated electronically
– but retain display
• how?
– small spheres turned
– or channels with coloured liquid
and contrasting spheres
– rapidly developing area
Digital paper
62
steering wheels, knobs and dials … just like real!
cockpit and virtual controls
63
six-degrees of movement: x, y, z + roll, pitch, yaw
the 3D mouse
64
fibre optics used to detect finger position
data glove
65
detect head motion and possibly eye gaze
VR helmets
66
accelerometers strapped to limbs or reflective dots
and video processing
whole body tracking
67
desktop VR
– ordinary screen, mouse or keyboard control
– perspective and motion give 3D effect
• seeing in 3D
– use stereoscopic vision
– VR helmets
– screen plus shuttered specs, etc
3D displays
68
small TV screen for each eye
• slightly different angles
• 3D effect
VR headsets
69
time delay
– move head … lag … display moves
– conflict: head movement vs. eyes
• depth perception
– headset gives different stereo distance
– but all focused in same plane
– conflict: eye angle vs. focus
• conflicting cues => sickness
– helps motivate improvements in technology
VR motion sickness
70
scenes projected on walls
• realistic environment
• hydraulic rams!
• real controls
• other people
simulators and VR caves
71
dials, gauges, lights, etc.
analogue representations
72
small LCD screens, LED lights, etc
digital displays:
73
found in aircraft cockpits
– show most important controls
… depending on context
head-up displays
74
beeps, bongs, clonks, whistles and
whirrs
• used for error indications
• confirmation of actions e.g. key
Sounds
75
touch and feeling important
– in games … vibration, force feedback
– in simulation … feel of surgical instruments
– called haptic devices
• texture, smell, taste
– current technology very limited
Touch, feel, smell
76
for controlling menus
• feel small ‘bumps’ for each item
• makes it easier to select options by feel
• uses haptic technology from Immersion Corp.
BMW iDrive
77
specialist controls needed …
– industrial controls, consumer products, etc
physical controls
78
sensors all around us
– car courtesy light – small switch on door
– ultrasound detectors – security, washbasins
– RFID security tags in shops
– temperature, weight, location
• … and even our own bodies …
– iris scanners, body temperature, heart rate,
galvanic skin response, blink rate
Environment and bio-sensing
79
image made from small dots
– allows any character set or graphic to be
printed,
• critical features:
– resolution
• size and spacing of the dots
• measured in dots per inch (dpi)
– speed
• usually measured in pages per minute
– cost!!
Printing
80
Types of dot-based printers
dot-matrix printers
ink-jet and bubble-jet printers
laser printer
81
use inked ribbon (like a typewriter
– line of pins that can strike the ribbon, dotting the paper.
– typical resolution 80-120 dpi
dot-matrix printers
82
tiny blobs of ink sent from print head to paper
– typically 300 dpi or better .
ink-jet and bubble-jet printers
83
like photocopier: dots of electrostatic charge deposited on
drum, which picks up toner (black powder form of ink)
rolled onto paper which is then fixed with heat
– typically 600 dpi or better.
laser printer
84
dot matrix
– same print head used for several paper rolls
– may also print cheques
shop tills
85
special heat-sensitive paper
– paper heated by pins makes a dot
– poor quality, but simple & low maintenance
– used in some fax machines
thermal printers
86
the particular style of text
Courier font
Helvetica font
Palatino font
Times Roman font
§´ (special symbol)
Font
87
fixed-pitch – every character has the same width
e.g. Courier
– variable-pitched – some characters wider
e.g. Times Roman – compare the ‘i’ and the “m”
Pitch
88
sans-serif – square-ended strokes
e.g. Helvetica
– serif – with splayed ends (such as)
e.g. Times Roman or Palatino
Serif or Sans-serif
89
easy to read shape of words
lowercase
90
better for individual letters and non-words
e.g. flight numbers: BA793 vs. ba793
UPPERCASE
91
helps your eye on long lines of printed text
– but sans serif often better on screen
serif fonts
92
Pages very complex
– different fonts, bitmaps, lines, digitised photos, etc.
• Can convert it all into a bitmap and send to the printer
… but often huge !
• Alternatively Use a page description language
– sends a description of the page can be sent,
– instructions for curves, lines, text in different styles, etc.
– like a programming language for printing!
• PostScript is the most common
Page Description Languages
93
WYSIWYG
– what you see is what you get
– aim of word processing, etc.
• but …
– screen: 72 dpi, landscape image
– print: 600+ dpi, portrait
• can try to make them similar
but never quite the same
• so … need different designs, graphics etc, for
screen and print
Screen and page
94
Take paper and convert it into a bitmap
• Two sorts of scanner
– flat-bed: paper placed on a glass plate, whole page
converted into bitmap
– hand-held: scanner passed over paper, digitising strip
typically 3-4” wide
• Shines light at paper and note intensity of reflection
– colour or greyscale
• Typical resolutions from 600–2400 dpi
Scanners
95
OCR converts bitmap back into text
• different fonts
– create problems for simple “template
matching” algorithms
– more complex systems segment text,
decompose it into lines and arcs, and
decipher characters that way
• page format
– columns, pictures, headers and footers
Optical character recognition
96
paper usually regarded as output only
• can be input too – OCR, scanning, etc.
• Xerox PaperWorks
– glyphs – small patterns of /\\//\\\
• used to identify forms etc.
• used with scanner and fax to control applications
• more recently
– papers micro printed - like wattermarks
• identify which sheet and where you are
– special ‘pen’ can read locations
• know where they are writing
Paper-based interaction
97
Random access memory (RAM)
– on silicon chips
– 100 nano-second access time
– usually volatile (lose information if power turned off)
– data transferred at around 100 Mbytes/sec
• Some non-volatile RAM used to store basic
set-up information
• Typical desktop computers:
64 to 256 Mbytes RAM
Short-term Memory - RAM
98
magnetic disks
– floppy disks store around 1.4 Mbytes
– hard disks typically 40 Gbytes to 100s of Gbytes
access time ~10ms, transfer rate 100kbytes/s
• optical disks
– use lasers to read and sometimes write
– more robust that magnetic media
– CD-ROM
- same technology as home audio, ~ 600 Gbytes
– DVD - for AV applications, or very large files
Long-term Memory - disks
99
Long-term Memory - disks
magnetic disks
optical disks
100
PDAs
– often use RAM for their main memory
• Flash-Memory
– used in PDAs, cameras etc.
– silicon based but persistent
– plug-in USB devices for data transfer
Blurring boundaries
101
often use RAM for their main memory
PDAs
102
used in PDAs, cameras etc.
– silicon based but persistent
– plug-in USB devices for data transfer
Flash-Memory
103
what do the numbers mean?
• some sizes (all uncompressed) …
– this book, text only ~ 320,000 words, 2Mb
– the Bible ~ 4.5 Mbytes
– scanned page ~ 128 Mbytes
• (11x8 inches, 1200 dpi, 8bit greyscale)
– digital photo ~ 10 Mbytes
• (2–4 mega pixels, 24 bit colour)
– video ~ 10 Mbytes per second
• (512x512, 12 bit colour, 25 frames per sec)
speed and capacity
104
Problem:
– running lots of programs + each program large
– not enough RAM
• Solution - Virtual memory :
– store some programs temporarily on disk
– makes RAM appear bigger
• But … swopping
– program on disk needs to run again
– copied from disk to RAM
– s l o w s t h i n g s d o w n
virtual memory
105
reduce amount of storage required
• lossless
– recover exact text or image – e.g. GIF, ZIP
– look for commonalities:
• text: AAAAAAAAAABBBBBCCCCCCCC 10A5B8C
• video: compare successive frames and store change
• lossy
– recover something like original – e.g. JPEG, MP3
– exploit perception
• JPEG: lose rapid changes and some colour
• MP3: reduce accuracy of drowned out notes
Compression
106
7-bit binary code for to each letter and
character
ASCII
107
8-bit encoding of 16 bit character set
UTF-8
108
text plus formatting and layout information
RTF
109
documents regarded as structured objects
SGML
110
simpler version of SGML for web applications
XML
111
many storage formats :
(PostScript, GIFF, JPEG, TIFF, PICT, etc.)
– plus different compression techniques
(to reduce their storage requirements
Images
112
again lots of formats :
(QuickTime, MPEG, WAV, etc.)
– compression even more important
– also ‘streaming’ formats for network delivery
Audio/Video
113
large information store
– long time to search => use index
– what you index -> what you can access
• simple index needs exact match
• forgiving systems:
– Xerox “do what I mean” (DWIM)
– SOUNDEX – McCloud ~ MacCleod
• access without structure …
– free text indexing (all the words in a document)
– needs lots of space!!
methods of access
114
Designers tend to assume fast processors, and make
interfaces more and more complicated
• But problems occur, because processing cannot keep up
with all the tasks it needs to do
– cursor overshooting because system has buffered
keypresses
– icon wars - user clicks on icon, nothing happens, clicks on
another, then system responds and windows fly
everywhere
• Also problems if system is too fast - e.g. help screens
may scroll through text much too rapidly to be read
Finite processing speed
115
computers get faster and faster!
• 1965 …
– Gordon Moore, co-founder of Intel, noticed a pattern
– processor speed doubles every 18 months
– PC … 1987: 1.5 Mhz, 2002: 1.5 GHz
• similar pattern for memory
– but doubles every 12 months!!
– hard disk … 1991: 20Mbyte : 2002: 30 Gbyte
• baby born today
– record all sound and vision
– by 70 all life’s memories stored in a grain of dust!
Moore’s law
116
implicit assumption … no delays
an infinitely fast machine
• what is good design for real machines?
• good example … the telephone :
– type keys too fast
– hear tones as numbers sent down the line
– actually an accident of implementation
– emulate in deisgn
the myth of the infinitely
fast machine
117
Computation takes ages, causing frustration for the user
Computation bound
118
Bottleneck in transference of data from disk to memory
Storage channel bound
119
Common bottleneck: updating displays requires a lot of
effort - sometimes helped by adding a graphics coprocessor optimised to take on the burden
Graphics bound
120
Many computers networked - shared resources and files,
access to printers etc. - but interactive performance can be
reduced by slow network speed
Network capacity
121
Networks allow access to …
– large memory and processing
– other people (groupware, email)
– shared resources – esp. the web
Issues
– network delays – slow feedback
– conflicts - many people update data
– unpredictability
Networked computing
122
history of internet
1969: DARPANET US DoD, 4 sites
– 1971: 23; 1984: 1000; 1989: 10000
123
common language (protocols):
TCP
IP
email, HTTP, all build on top of these
124
lower level, packets (like letters) between machines
TCP – Transmission Control protocol
125
reliable channel (like phone call) between programs on
machines
IP – Internet Protocol
