chapter 2the computer

The Computera computer system is made up of various elements

each of these elements affects the interactioninput devices text entry and pointingoutput devices screen (small&large), digital papervirtual reality special interaction and display devicesphysical interaction e.g. sound, haptic, bio-sensingpaper as output (print) and input (scan)memory RAM & permanent media, capacity & accessprocessing speed of processing, networks

Interacting with computersto understand humancomputer interaction need to understand computers!

A typical computer systemscreen, or monitor, on which there are windowskeyboardmouse/trackpad

variationsdesktoplaptopPDA

the devices dictate the styles of interaction that the system supportsIf we use different devices, then the interface will support a different style of interaction

How many computers in your house?hands up, none, 1, 2 , 3, more!!

computers in your pockets?are you thinking PC, laptop, PDA ??

How many computers in your house?

PCTV, VCR, DVD, HiFi, cable/satellite TVmicrowave, cooker, washing machinecentral heatingsecurity system

can you think of more?in your pockets?

PDAphone, camerasmart card, card with magnetic strip?electronic car keyUSB memory

try your pockets and bags

Interactivity?Long ago in a galaxy far away batch processingpunched card stacks or large data files preparedlong wait .line printer output and if it is not right

Now most computing is interactiverapid feedbackthe user in control (most of the time)doing rather than thinking

Is faster always better?

Richer interactionsensorsand deviceseverywhere

text entry deviceskeyboards (QWERTY et al.)chord keyboards, phone padshandwriting, speech

KeyboardsMost common text input deviceAllows rapid entry of text by experienced users

Keypress closes connection, causing a character code to be sentUsually connected by cable, but can be wireless

layout QWERTYStandardised layoutbut non-alphanumeric keys are placed differentlyaccented symbols needed for different scriptsminor differences between UK and USA keyboards

QWERTY arrangement not optimal for typing layout to prevent typewriters jamming!Alternative designs allow faster typing but large social base of QWERTY typists produces reluctance to change.

QWERTY (ctd)

alternative keyboard layoutsAlphabetickeys arranged in alphabetic ordernot faster for trained typistsnot faster for beginners either!

Dvorakcommon letters under dominant fingersbiased towards right handcommon combinations of letters alternate between hands10-15% improvement in speed and reduction in fatigueBut - large social base of QWERTY typists produce market pressures not to change

special keyboardsdesigns to reduce fatigue for RSIfor one handed usee.g. the Maltron left-handed keyboard

Chord keyboardsonly a few keys - four or 5letters typed as combination of keypressescompact size ideal for portable applicationsshort learning time keypresses reflect letter shapefast once you have trained

BUT - social resistance, plus fatigue after extended useNEW niche market for some wearables

phone pad and T9 entryuse numeric keys with multiple presses2 a b c6 - m n o3 - d e f7 - p q r s4 - g h i8 - t u v5 - j k l9 - w x y zhello = 4433555[pause]555666surprisingly fast!

T9 predictive entrytype as if single key for each letteruse dictionary to guess the right wordhello = 43556 but 26 -> menu am or an

Handwriting recognitionText can be input into the computer, using a pen and a digesting tabletnatural interaction

Technical problems:capturing all useful information - stroke path, pressure, etc. in a natural mannersegmenting joined up writing into individual lettersinterpreting individual letterscoping with different styles of handwriting

Used in PDAs, and tablet computers leave the keyboard on the desk!

Speech recognitionImproving rapidly

Most successful when:single user initial training and learns peculiaritieslimited vocabulary systems

Problems withexternal noise interferingimprecision of pronunciationlarge vocabulariesdifferent speakers

Numeric keypadsfor entering numbers quickly:calculator, PC keyboardfor telephones

not the same!!

ATM like phone

telephonecalculator

positioning, pointing and drawingmouse, touchpad trackballs, joysticks etc. touch screens, tablets eyegaze, cursors

the MouseHandheld pointing devicevery commoneasy to use

Two characteristicsplanar movementbuttons(usually from 1 to 3 buttons on top, used for making a selection, indicating an option, or to initiate drawing etc.)

the mouse (ctd)Mouse located on desktoprequires physical spaceno arm fatigue

Relative movement only is detectable.Movement of mouse moves screen cursorScreen cursor oriented in (x, y) plane, mouse movement in (x, z) plane

an indirect manipulation device.device itself doesnt obscure screen, is accurate and fast.hand-eye coordination problems for novice users

How does it work?Two methods for detecting motion

MechanicalBall on underside of mouse turns as mouse is movedRotates orthogonal potentiometersCan be used on almost any flat surface

Opticallight emitting diode on underside of mousemay use special grid-like pad or just on deskless susceptible to dust and dirtdetects fluctuating alterations in reflected light intensity to calculate relative motion in (x, z) plane

Even by foot some experiments with the footmousecontrolling mouse movement with feet not very common :-)

but foot controls are common elsewhere:car pedalssewing machine speed controlorgan and piano pedals

Touchpadsmall touch sensitive tabletsstroke to move mouse pointerused mainly in laptop computers

good acceleration settings importantfast strokelots of pixels per inch movedinitial movement to the targetslow strokeless pixels per inchfor accurate positioning

Trackball and thumbwheelsTrackballball is rotated inside static housinglike an upsdie down mouse!relative motion moves cursorindirect device, fairly accurateseparate buttons for pickingvery fast for gamingused in some portable and notebook computers.

Thumbwheels for accurate CAD two dials for X-Y cursor positionfor fast scrolling single dial on mouse

Joystick and keyboard nippleJoystickindirect pressure of stick = velocity of movement buttons for selection on top or on front like a triggeroften used for computer games aircraft controls and 3D navigation

Keyboard nipplefor laptop computersminiature joystick in the middle of the keyboard

Touch-sensitive screenDetect the presence of finger or stylus on the screen.works by interrupting matrix of light beams, capacitance changes or ultrasonic reflectionsdirect pointing device

Advantages:fast, and requires no specialised pointergood for menu selectionsuitable for use in hostile environment: clean and safe from damage.

Disadvantages:finger can mark screenimprecise (finger is a fairly blunt instrument!)difficult to select small regions or perform accurate drawinglifting arm can be tiring

Stylus and light penStylussmall pen-like pointer to draw directly on screenmay use touch sensitive surface or magnetic detectionused in PDA, tablets PCs and drawing tables

Light Pennow rarely useduses light from screen to detect location

BOTH very direct and obvious to usebut can obscure screen

Digitizing tabletMouse like-device with cross hairs

used on special surface - rather like stylus

very accurate - used for digitizing maps

Eyegazecontrol interface by eye gaze directione.g. look at a menu item to select ituses laser beam reflected off retina a very low power laser! mainly used for evaluation (ch x)potential for hands-free controlhigh accuracy requires headsetcheaper and lower accuracy devices available sit under the screen like a small webcam

Cursor keysFour keys (up, down, left, right) on keyboard.Very, very cheap, but slow. Useful for not much more than basic motion for text-editing tasks.No standardised layout, but inverted T, most common

Discrete positioning controlsin phones, TV controls etc.cursor pads or mini-joysticksdiscrete left-right, up-downmainly for menu selection

display devicesbitmap screens (CRT & LCD)large & situated displays digital paper

bitmap displaysscreen is vast number of coloured dots

resolution and colour depthResolution used (inconsistently) fornumber of pixels on screen (width x height)e.g. SVGA 1024 x 768, PDA perhaps 240x400density of pixels (in pixels or dots per inch - dpi)typically between 72 and 96 dpiAspect ratioration between width and height4:3 for most screens, 16:9 for wide-screen TVColour depth:how many different colours for each pixel?black/white or greys only256 from a pallete8 bits each for red/green/blue = millions of colours

anti-aliasingJaggiesdiagonal lines that have discontinuities in due to horizontal raster scan process.

Anti-aliasingsoftens edges by using shades of line colouralso used for text

Cathode ray tubeStream of electrons emitted from electron gun, focused and directed by magnetic fields, hit phosphor-coated screen which glowsused in TVs and computer monitors

Health hazards of CRT !X-rays: largely absorbed by screen (but not at rear!)UV- and IR-radiation from phosphors: insignificant levelsRadio 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 hints do not sit too close to the screendo not use very small fontsdo not look at the screen for long periods without a breakdo not place the screen directly in front of a bright windowwork in well-lit surroundings

Take extra care if pregnant. but also posture, ergonomics, stress

Liquid crystal displaysSmaller, 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 colourN.B. light reflected not emitted => less eye strain

special displaysRandom Scan (Directed-beam refresh, vector display)draw the lines to be displayed directlyno jaggieslines need to be constantly redrawnrarely used except in special instrumentsDirect view storage tube (DVST)Similar to random scan but persistent => no flickerCan be incrementally updated but not selectively erasedUsed in analogue storage oscilloscopes

large displaysused for meetings, lectures, etc.technologyplasma usually wide screenvideo walls lots of small screens togetherprojected RGB lights or LCD projectorhand/body obscures screenmay be solved by 2 projectors + clever software back-projectedfrosted glass + projector behind

situated displaysdisplays in public placeslarge or smallvery public or for small groupdisplay onlyfor information relevant to locationor interactiveuse stylus, touch sensitive screemin all cases the location mattersmeaning of information or interaction is related to the location

small displays beside office doorshandwritten notes left using stylusoffice owner reads notes using web interface

Hermes a situated displaysmall displays beside office doorshandwrittennotes left using stylusoffice owner reads notes using web interface

Digital paperwhat?thin flexible sheetsupdated electronicallybut retain display

how?small spheres turnedor channels with coloured liquid and contrasting spheresrapidly developing area

appearancecrosssection

virtual reality and 3D interactionpositioning in 3D space moving and graspingseeing 3D (helmets and caves)

positioning in 3D spacecockpit and virtual controlssteering wheels, knobs and dials just like real!the 3D mousesix-degrees of movement: x, y, z + roll, pitch, yaw data glovefibre optics used to detect finger positionVR helmetsdetect head motion and possibly eye gazewhole body trackingaccelerometers strapped to limbs or reflective dots and video processing

pitch, yaw and rollpitchyawroll

3D displaysdesktop VRordinary screen, mouse or keyboard controlperspective and motion give 3D effectseeing in 3Duse stereoscopic visionVR helmetsscreen plus shuttered specs, etc.

also see extra slides on 3D vision

VR headsetssmall TV screen for each eyeslightly different angles3D effect

VR motion sicknesstime delaymove head lag display movesconflict: head movement vs. eyesdepth perceptionheadset gives different stereo distancebut all focused in same planeconflict: eye angle vs. focusconflicting cues => sicknesshelps motivate improvements in technology

simulators and VR cavesscenes projected on wallsrealistic environmenthydraulic rams!real controlsother people

physical controls, sensors etc.special displays and gaugessound, touch, feel, smellphysical controlsenvironmental and bio-sensing

dedicated displaysanalogue representations:dials, gauges, lights, etc.

digital displays:small LCD screens, LED lights, etc.

head-up displays found in aircraft cockpitsshow most important controls depending on context

Soundsbeeps, bongs, clonks, whistles and whirrs

used for error indications

confirmation of actions e.g. keyclick

also see chapter 10

Touch, feel, smelltouch and feeling importantin games vibration, force feedbackin simulation feel of surgical instrumentscalled haptic devices

texture, smell, tastecurrent technology very limited

BMW iDrivefor controlling menusfeel small bumps for each itemmakes it easier to select options by feel uses haptic technology from Immersion Corp.

physical controlsspecialist controls needed industrial controls, consumer products, etc.

large buttonsclear dialstiny buttonsmulti-function controleasy-cleansmooth buttons

Environment and bio-sensingsensors all around uscar courtesy light small switch on doorultrasound detectors security, washbasinsRFID security tags in shopstemperature, weight, location

and even our own bodies iris scanners, body temperature, heart rate, galvanic skin response, blink rate

paper: printing and scanningprint technologyfonts, page description, WYSIWYGscanning, OCR

Printingimage made from small dotsallows any character set or graphic to be printed,critical features:resolutionsize and spacing of the dotsmeasured in dots per inch (dpi)speedusually measured in pages per minutecost!!

Types of dot-based printersdot-matrix printersuse inked ribbon (like a typewriterline of pins that can strike the ribbon, dotting the paper.typical resolution 80-120 dpiink-jet and bubble-jet printerstiny blobs of ink sent from print head to papertypically 300 dpi or better .laser printerlike 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 heattypically 600 dpi or better.

Printing in the workplaceshop tillsdot matrixsame print head used for several paper rollsmay also print cheques

thermal printersspecial heat-sensitive paperpaper heated by pins makes a dotpoor quality, but simple & low maintenanceused in some fax machines

FontsFont the particular style of text

Courier fontHelvetica fontPalatino fontTimes Roman font~ (special symbol)

Size of a font measured in points (1 pt about 1/72) (vaguely) related to its height

This is ten point HelveticaThis is twelve pointThis is fourteen pointThis is eighteen pointand this is twenty-four point

Fonts (ctd)Pitchfixed-pitch every character has the same widthe.g. Couriervariable-pitched some characters widere.g. Times Roman compare the i and the mSerif or Sans-serifsans-serif square-ended strokese.g. Helveticaserif with splayed ends (such as)e.g. Times Roman or Palatino

Readability of textlowercaseeasy to read shape of wordsUPPERCASEbetter for individual letters and non-words e.g. flight numbers: BA793 vs. ba793

serif fontshelps your eye on long lines of printed textbut sans serif often better on screen

Page Description LanguagesPages very complexdifferent 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 languagesends 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

Screen and pageWYSIWYGwhat you see is what you getaim of word processing, etc. but screen: 72 dpi, landscape imageprint: 600+ dpi, portraitcan try to make them similar but never quite the sameso need different designs, graphics etc, for screen and print

ScannersTake paper and convert it into a bitmap

Two sorts of scannerflat-bed: paper placed on a glass plate, whole page converted into bitmaphand-held: scanner passed over paper, digitising strip typically 3-4 wide

Shines light at paper and note intensity of reflectioncolour or greyscale

Typical resolutions from 6002400 dpi

Scanners (ctd)Used in

desktop publishing for incorporating photographs and other images

document storage and retrieval systems, doing away with paper storage

special scanners for slides and photographic negatives

Optical character recognitionOCR converts bitmap back into textdifferent fontscreate problems for simple template matching algorithmsmore complex systems segment text, decompose it into lines and arcs, and decipher characters that waypage formatcolumns, pictures, headers and footers

Paper-based interactionpaper usually regarded as output only

can be input too OCR, scanning, etc.

Xerox PaperWorksglyphs small patterns of /\\//\\\used to identify forms etc.used with scanner and fax to control applications

more recentlypapers micro printed - like wattermarksidentify which sheet and where you arespecial pen can read locationsknow where they are writing

memoryshort term and long termspeed, capacity, compressionformats, access

Short-term Memory - RAMRandom access memory (RAM)on silicon chips100 nano-second access timeusually 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

Long-term Memory - disksmagnetic disksfloppy disks store around 1.4 Mbyteshard disks typically 40 Gbytes to 100s of Gbytes access time ~10ms, transfer rate 100kbytes/s

optical disksuse lasers to read and sometimes writemore robust that magnetic mediaCD-ROM - same technology as home audio, ~ 600 GbytesDVD - for AV applications, or very large files

Blurring boundariesPDAsoften use RAM for their main memory

Flash-Memoryused in PDAs, cameras etc.silicon based but persistentplug-in USB devices for data transfer

speed and capacitywhat do the numbers mean?

some sizes (all uncompressed) this book, text only ~ 320,000 words, 2Mbthe Bible ~ 4.5 Mbytesscanned page ~ 128 Mbytes(11x8 inches, 1200 dpi, 8bit greyscale)digital photo ~ 10 Mbytes(24 mega pixels, 24 bit colour) video ~ 10 Mbytes per second(512x512, 12 bit colour, 25 frames per sec)

virtual memoryProblem:running lots of programs + each program largenot enough RAM

Solution - Virtual memory :store some programs temporarily on diskmakes RAM appear bigger

But swoppingprogram on disk needs to run againcopied from disk to RAMs l o w s t h i n g s d o w n

Compressionreduce amount of storage requiredlosslessrecover exact text or image e.g. GIF, ZIPlook for commonalities:text: AAAAAAAAAABBBBBCCCCCCCC 10A5B8Cvideo: compare successive frames and store changelossyrecover something like original e.g. JPEG, MP3exploit perceptionJPEG: lose rapid changes and some colourMP3: reduce accuracy of drowned out notes

Storage formats - textASCII - 7-bit binary code for to each letter and characterUTF-8 - 8-bit encoding of 16 bit character setRTF (rich text format) - text plus formatting and layout informationSGML (standardized generalised markup language) - documents regarded as structured objects XML (extended markup language) - simpler version of SGML for web applications

Storage formats - mediaImages:many storage formats : (PostScript, GIFF, JPEG, TIFF, PICT, etc.)plus different compression techniques (to reduce their storage requirements)

Audio/Videoagain lots of formats : (QuickTime, MPEG, WAV, etc.)compression even more importantalso streaming formats for network delivery

methods of accesslarge information storelong time to search => use indexwhat you index -> what you can accesssimple index needs exact matchforgiving systems:Xerox do what I mean (DWIM)SOUNDEX McCloud ~ MacCleodaccess without structure free text indexing (all the words in a document)needs lots of space!!

processing and networksfinite speed (but also Moores law)limits of interactionnetworked computing

Finite processing speedDesigners 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 docursor overshooting because system has buffered keypressesicon 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

Moores lawcomputers get faster and faster!1965 Gordon Moore, co-founder of Intel, noticed a patternprocessor speed doubles every 18 monthsPC 1987: 1.5 Mhz, 2002: 1.5 GHzsimilar pattern for memorybut doubles every 12 months!!hard disk 1991: 20Mbyte : 2002: 30 Gbytebaby born todayrecord all sound and visionby 70 all lifes memories stored in a grain of dust!/e3/online/moores-law/

the myth of the infinitely fast machine

implicit assumption no delays an infinitely fast machinewhat is good design for real machines?good example the telephone :type keys too fasthear tones as numbers sent down the lineactually an accident of implementationemulate in deisgn

Limitations on interactive performanceComputation boundComputation takes ages, causing frustration for the userStorage channel boundBottleneck in transference of data from disk to memoryGraphics boundCommon bottleneck: updating displays requires a lot of effort - sometimes helped by adding a graphics co-processor optimised to take on the burdenNetwork capacityMany computers networked - shared resources and files, access to printers etc. - but interactive performance can be reduced by slow network speed

Networked computingNetworks allow access to large memory and processingother people (groupware, email)shared resources esp. the web

Issuesnetwork delays slow feedbackconflicts - many people update dataunpredictability

The internethistory 1969: DARPANET US DoD, 4 sites1971: 23; 1984: 1000; 1989: 10000 common language (protocols):TCP Transmission Control protocollower level, packets (like letters) between machinesIP Internet Protocolreliable channel (like phone call) between programs on machinesemail, HTTP, all build on top of these