Chapter 2 – The Computer

Overview

Chapter 2 – The Computer

Study Summary

• Computer system elements affecting the user:

• Input devices: Text entry — keyboard, phone text entry, speech and handwriting; Pointing — mouse, touchpad, stylus; 3D interaction devices.

• Output display devices: bitmap display; Large displays; situated displays; Digital paper.

• Virtual reality systems and 3D visualization.

• Physical world devices: Physical controls and dedicated displays; Sound, smell and haptic feedback; Sensors for movement, temperature, bio-signs.

• Paper output and input: Printers; Scanners; optical character recognition.

• Memory: Short-term memory (R.A.M); Long-term memory (magnetic and optical disks); Capacity limitations and access methods.

• Processing: systems running too slow or too fast; Myth of the infinitely fast machine; Processing speed limitations; Networks and system performance.

2.1 Introduction

• Interaction is a process of information transfer from user to computer and computer to user.

• Main examples: Keyboard, Mouse, Screen, Virtual reality and 3D interaction, Physical interactions, Printers and scanners, Processor and memory, Networks.

• Technology influences nature/style of interaction and interface. Need to understand storage capacity and computational power.

• Batch processing: large mass input, minimal interaction, hours/days.

• Typical desktop: interaction in seconds/fractions of seconds.

• Richer interaction – everywhere, everywhere: computers embedded in appliances, phones, security systems, webcams, etcetera

2.2 Text Entry Devices

• Main forms: Alphanumeric keyboard; Chord keyboards; Phone pad and T.9 entry; Handwriting recognition; Speech recognition.

2.2.1 The alphanumeric keyboard

• qwerty keyboard is common. Used for textual data and commands.

• qwerty named after first six letters of top row. Originated with mechanical typewriters.

• Modern computers no longer have original mechanical limitations, but qwerty remains dominant due to social resistance, trained typists, replacement costs, relearning. This is an example of technological inertia.

• Keypress closes connection and sends character code. Key feel, pressure, key travel, half-travel keyboards, feedback are relevant.

• Alphabetic keyboard does not provide major typing-speed advantage.

• Dvorak keyboard: 56% keystrokes right hand; alternates hands; 70% keystrokes home row; designed to reduce fatigue/increase speed. Studies described in the chapter found 10 to 15% speed improvement and reduced fatigue.

• Ergonomic keyboard designs reduce strain/R.S.I and improve ergonomic position.

2.2.2 Chord Keyboards

• Few keys, often 4 or 5. Letters produced by pressing one or more keys at once.

• Compact, one-handed, potentially fast. Courtroom stenographers.

• Not mainstream due to lack of familiarity/social resistance.

Numeric Keypads

• Calculator style: 123 at bottom. Telephone style: 123 at top. Layout depends on users/task.

2.2.3 Phone Pad and T.9 Entry

• Mobile phones use numeric keys.

• 2 equals a b c; 3 equals d e f; 4 equals g h i; 5 equals j k l; 6 equals m n o; 7 equals p q r s; 8 equals t u v; 9 equals w x y z.

• Multiple presses select letters. T.9 uses dictionary to disambiguate words. Example given in the chapter: 3926753 to example.

2.2.4 Handwriting Recognition

• Familiar/intuitive.

• Problems: inaccurate recognition, individual handwriting differences, stroke information, writing speed.

• Online recognition easier than reading handwritten paper because stroke information can be captured.

• Useful for notes, sketches, diaries, address books, organizers.

• Different input device enables alternative interface designs. Signature authentication can use stroke patterns.

2.2.5 Speech Recognition

• Talk to machine and respond to commands.

• Problems: recognition errors, natural language vagueness, speaker differences, accents, cold/emotion, background noise, office noise, confidentiality.

• Niche markets: telephone information systems; access for disabled users; hands-occupied situations; R.S.I.

• Possibilities: 1. Replace keyboard input; 2. Redesign around speech; 3. Use speech where keyboard is impractical/impossible.

2.3 Positioning, Pointing and Drawing

• Pointing devices support pointing, positioning, selecting, drawing. Mouse common desktop; Touchpad common laptop.

2.3.1 The Mouse

• Detects movement and moves screen pointer/cursor. One/two/three buttons. Selection, actions, single-click, double-click.

• Indirect input device.

• Advantages: easy movement, little arm fatigue, small cursor, does not obscure display.

• Developed around 1964 by Douglas C. Engelbart.

• Optical mice use L.E.D and sensor to detect relative x,y motion. Less susceptible to dust/dirt than mechanical mice.

2.3.2 Touchpad

• Touch-sensitive tablet. Finger movement controls screen.

• Acceleration settings change finger-to-screen movement relationship. Slow movement leads to small screen movement; fast movement leads to larger movement.

2.3.3 Trackball and Thumbwheel

• Trackball: Upside-down mouse; Compact; No extra operating space; Fairly accurate; Difficult for long drawing movements.

• Thumbwheel: Two orthogonal dials; Cheap; Exact horizontal/vertical movement; Useful in C-A-D; Single thumbwheel for scrolling.

2.3.4 Joystick and Keyboard Nipple

• Joystick: Indirect input; Absolute joystick; Isometric joystick; Isometric joystick: pressure controls cursor velocity; Used in computer games.

• Keyboard nipple: Small rubber device; Isometric joystick; Controls rate of movement.

2.3.5 Touch-Sensitive Screens (Touchscreen)

• Direct devices.

• Advantages: fast, no specialized pointing device, menu selection, intuitive, public systems, hostile environments.

• Disadvantages: greasy marks, finger inaccurate for small regions, accurate drawing difficult, arm fatigue.

• Chapter states optimal angle around 15 degrees up from horizontal.

2.3.6 Stylus and Light Pen

• Stylus: pen-like pointing/drawing device.

• Light pen: detects light from screen phosphor and can address individual pixels.

• Direct devices: Stylus, Light pen, Touchscreen.

• Indirect devices: Mouse, Touchpad, Joystick, Trackball.

• Direct devices can obscure display with user's hand.

2.3.7 Digitizing Tablet

• Freehand drawing; High-resolution drawing; Maps; Mouse substitute; Handwriting recognition.

• Types: resistive, magnetic, capacitative, electrostatic, sonic.

• Can detect relative or absolute motion; indirect device.

2.3.8 Eyegaze

• Control computer by looking.

• Advantages: very fast, accurate, selection, disabled users, H.C.I evaluation.

• Disadvantages: expensive, calibration, not suitable for drawing, difficult to distinguish deliberate gaze from accidental glance.

2.3.9 Cursor Keys and Discrete Positioning

• Up/down/left/right. Useful for lists, menus, spreadsheet cells, text movement.

• Mobile phones/T.V remotes use discrete controls.

2.4 Display Devices

• Most interactive systems use display screens.

2.4.1 Bitmap Displays – Resolution and Color

• Bitmap = many colored dots called pixels in rectangular grid. Black/white, grayscale, full color.

• More bits per pixel arrow more color slash intensity possibilities.

• Resolution: 1. Total pixels; 2. Density in pixels per inch.

• Jaggies = rough edges on diagonal/curved lines. Anti-aliasing = softens edges to reduce jaggies.

2.4.2 Technologies

• C.R.T: Electron gun; Magnetic fields; Phosphor-coated screen; Scanning electron beam.

• C.R.T advantages: cheap, fast response, high color. Disadvantages: bulky, resolution increases price, flicker/eyestrain, image smearing with high-persistence phosphor.

• L.C.D: Smaller, lighter, lower power, flat-panel, matrix addressable. Enabled notebook/portable computer market. Less noticeable flicker/reduced eyestrain compared with standard C.R.T.

2.4.3 Large Displays and Situated Displays

• Large displays: meeting rooms, lectures, shops, garages, public information.

• Situated displays: placed in particular physical locations and provide location-appropriate information.

2.4.4 Digital Paper

• Thin/flexible display. Can be written electronically. Retains contents when removed from electrical supply.

2.5 Devices for Virtual Reality and 3D Interaction

• V.R requires navigation/interactions in 3D space.

• Shift from mouse to 3D devices: 2 degrees of freedom to 6 degrees of freedom.

2.5.1 Positioning in 3D Space

• Movement, position, orientation.

• 3D mouse tracks position, pitch, yaw, roll = six degrees of freedom.

• Dataglove detects joint angles of fingers/thumb.

• Whole-body tracking via sensors/cameras/image processing.

2.5.2 3D Displays

• Desktop V.R uses normal screen plus shadows, occlusion, perspective.

• Stereoscopic vision: each eye sees slightly different angle; brain assesses relative distance.

• 3D displays: two small screens, goggles, spectacles, polarized filters.

V.R Motion Sickness

• Caused by delay between user movement and scene movement. Delay greater than about 100 ms can be disorienting. Can cause nausea/motion sickness.

Simulators and V.R Caves

Cave = room with large displays around user for surrounding virtual world.

2.6 Physical Controls, Sensors and Special Devices

• Computers increasingly exist outside traditional keyboard-mouse-screen systems: Interactive T.V; In-car navigation; Personal entertainment; Special displays, sound, touch, smell, dedicated controls, environmental sensors, bio-signs.

2.6.1 Special Displays

• Dials; Gauges; Lights; L.E.D's; Head-up display.

• Head-up display gives important info directly in pilot's line of vision.

2.6.2 Sound Output

• Beeps, bongs, clanks, whistles, whirrs. Sound provides feedback. Keyboard click can confirm keypress.

2.6.3 Touch, Feel and Smell

• Haptic devices: Force; Resistance; Texture; Physical feedback.

• Medical V.R, electronic Braille displays, in-car controls. Can access very fast physical responses.

• Smell: Strong memory cue, increases immersion. Dynamic smell generation technically difficult due to many smell receptors.

2.6.4 Physical Controls

• Controls vary by task.

• Microwave: flat plastic sheet/soft buttons. Washing machine: switches/knobs. MiniDisc player: small multifunction controls.

• Dedicated controls designed for specific device/task.

• Haptic feedback/resistance can make controls natural and provide feedback. Texture can distinguish controls without looking.

2.6.5 Environment and Bio-Sensing

• Sensors detect: Temperature; Movement; Location; Weight; Audio; Video; Body temperature; Blink rate; Typing rate; Physiological signs.

• Examples: Automatic doors; Energy-saving lights; Security tags; G.P.S; Infrared sensors.

• Related to ubiquitous computing.

2.7 Paper: Printing and Scanning

- Paperless office idea: documents produced, dispatched, read, filed online. More realistic concept: less-paper office.

2.7.1 Printing

• Older: Line printer; Golf-ball printer; Daisy-wheel printer.

Modern/common: Dot-matrix — inked ribbon, pins, cheap to run, specialized/bulk printing; Ink-jet/bubble-jet — tiny ink blobs, quiet, near laser quality; Laser printer — photocopier-like, electrostatic charge/toner, near typeset-quality.

Fonts and Readability

• Terms: Typeface; Font; Serif; Variable-pitched font; Mathematical fonts; Gothic lettering; Cursive script.

- Lower case generally easier to read than Block Capitals because word shapes provide clues, though upper case can clarify individual letters/nonsense words.

2.7.3 Screen and Page

• wiz-ee-wig = "what you see is what you get."

• Screen and paper are different media. Screen lower resolution than printer.

• Screen additive color: red, green, blue. Printer subtractive color: cyan, magenta, yellow, black.

• Different size/aspect ratio. Fonts differ on screen/paper. Designers may need different graphic designs.

2.7.4 Scanners and Optical Character Recognition

• Printer: electronic document to paper. Scanner: paper to electronic form.

• Flat-bed and hand-held scanners. Scanners create bitmaps.

• O.C.R = optical character recognition; computer “reads” characters.

• Uses: document storage, retrieval, desktop publishing, electronic publishing, converting scans to text.

• O.C.R reduces storage compared with bitmap image storage.

Paper-Based Interaction

• Paper can be input medium. Printed form can contain identifying glyph. Printed to filled to scanned to recognized. Allows interaction without screens/keyboards.

2.8 Memory

• Levels: Short-term memory (S.T.M); Long-term memory (L.T.M). Also: Primary storage; Secondary storage.

• Important for interface designers: capacity and access methods.

2.8.1 R.A.M and Short-Term Memory (S.T.M)

• R.A.M = random access memory. Active information.

• Fast, silicon-chip memory, usually volatile, lost when power off.

• Non-volatile R.A.M retains data without power.

• Flash memory: relatively slow write, retains data, used in digital cameras/portable devices.

2.8.2 Disks and Long-Term Memory (L.T.M)

• Magnetic disks; Optical disks.

• Magnetic: floppy, hard disks. Important: access time, transfer rate, random reads.

• Optical: laser; C.D-ROM, recordable C.D, rewritable optical, D.V.D.

• worm = write-once read-many. Optical media more robust than magnetic disks.

2.8.3 Understanding Speed and Capacity

• S.T.M = small/fast. L.T.M = large/slower.

• Example: R.A.M 256 Mbytes, 10 ns; Hard disk 100 Gbytes, 7 ms.

• When R.A.M full, O.S may use paging/swapping between R.A.M/disk. Causes delays.

• von Neumann bottleneck = limitation between disk and main memory due to slower transfer.

• Lazy information transfer = load currently needed information and transfer more during idle moments.

2.8.4 Compression

• Reduces storage by exploiting redundancy.

• Huffman encoding; Run-length encoding; Video frame differencing; Fractal compression.

• Important for text, bitmaps, video, images.

2.8.5 Storage Format and Standards

• ascii = American standard code for information interchange; 7-bit standard printable/control characters.

• unicode = 16-bit extension, larger character range including Japanese Kanji.

• R.T.F = rich text format.

• S.G.M.L = standard generalized markup language.

X.M.L = extensible markup language; lightweight S.G.M.L version, widely used for web applications.

• Many formats and lack of universal standards.

2.8.6 Methods of Access

• Key fields: Indices; Multiple keys/indices; Free text databases; D.W.I.M = do what I mean; Soundex = words/names that sound similar.

• Goal: natural and error-tolerant information access.

2.9 Processing and Networks

• Processing too slow or too fast can affect interface.

• Moore's law: historical rapid growth in processor/transistor capacity.

• Increased processing/memory influenced H.C.I.

2.9.1 Effects of Finite Processor Speed

• Too slow: delayed feedback; buffered input; cursor tracking problems; frustration.

• Too fast: info disappears too quickly; animations too fast; cursor flashing inappropriate for some displays.

The Myth of the Infinitely Fast Machine

• Designing as if response is always immediate.

• Instead: plan for slow responses; provide feedback; consider fixed delays where appropriate; account for system limitations.

2.9.2 Limitations on Interactive Performance

• Computation bound: processor limitation, for example find/replace large document.

• Progress feedback: counter, progress bar, cursor change.

• Storage channel bound: memory access limitation; compression trades storage space for processing time.

• Graphics bound: graphics operations can bottleneck.

• Graphics card can handle graphics and reduce main processor workload.

• Network capacity can limit remote file/resource access.

2.9.3 Networked Computing

• Provides: Communication; Remote resources; Shared information; Increased access to computing power/memory.

• Internet: originated from darpanet in 1969; developed into arpanet and Internet.

• T.C.P = Transmission Control Protocol. I.P = Internet Protocol. T.C.P/I.P.

• Networks can cause: delays; poor feedback; frustration; unpredictable responses.

• Networked systems can become an open loop because users/processes affect the system.

• Can violate: Consistency; Informative feedback; Predictable response.

Effect of Memory and Processing on H.C.I

• Increased processing/memory enabled: modern graphical interaction; larger programs; extra functionality; easier interaction; larger documents; multimedia; voice recognition; video/audio storage; electronic document storage.

• Growth in R.A.M/disks/optical storage removed many earlier arbitrary limits.

Most Important Topics to Memorize

• qwerty keyboard, Chord keyboard, Dvorak keyboard, T.9, Handwriting recognition, Speech recognition, Mouse, Touchpad, Trackball, Thumbwheel, Joystick, Touchscreen, Stylus, Light pen, Digitizing tablet, Eyegaze.

• Bitmap display, Pixels, Resolution, Anti-aliasing, C.R.T, L.C.D, Large displays, Situated displays, Digital paper.

• Virtual reality (V.R), Six degrees of freedom, 3D mouse, Dataglove, Stereoscopic vision, V.R motion sickness, Cave environments.

• Haptic devices, Ubiquitous computing.

• wiz-ee-wig, Optical character recognition (O.C.R).

• R.A.M, S.T.M, L.T.M, magnetic disks, optical disks, C.D-ROM, worm, Flash memory, Paging, Swapping, von Neumann bottleneck, Compression, ascii, unicode, R.T.F, S.G.M.L, X.M.L, D.W.I.M, Soundex.

- Moore's law, Myth of the infinitely fast machine, Computation bound, Storage channel bound, Graphics bound, Network capacity, Networked computing, T.C.P/I.P.