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The computer HCI

The document discusses various elements of computer systems and human-computer interaction. It describes input devices like keyboards, mice, touchscreens, as well as output displays such as CRT monitors, LCD screens, and digital paper. It also covers 3D interaction techniques used in virtual reality systems for positioning, movement, and viewing 3D content through helmets or caves. The document provides information on how these interaction techniques and devices work to facilitate human use of computer systems.

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chapter 2 the computer ARULKUMAR V - AP/CSE SECE
The Computer a computer system is made up of various elements each of these elements affects the interaction – input devices – text entry and pointing – output devices – screen (small&large), digital paper – virtual reality – special interaction and display devices – physical interaction – e.g. sound, haptic, bio-sensing – paper – as output (print) and input (scan) – memory – RAM & permanent media, capacity & access – processing – speed of processing, networks ARULKUMAR V - AP/CSE SECE
Interacting with computers to understand human–computer interaction … need to understand computers! what goes in and out devices, paper, sensors, etc. what can it do? memory, processing, networks ARULKUMAR V - AP/CSE SECE
A ‘typical’ computer system • screen, or monitor, on which there are windows • keyboard • mouse/trackpad • variations – desktop – laptop – PDA the devices dictate the styles of interaction that the system supports If we use different devices, then the interface will support a different style of interaction window 1 window 2 12-37pm ? ARULKUMAR V - AP/CSE SECE
How many … • computers in your house? – hands up, … … none, 1, 2 , 3, more!! • computers in your pockets? are you thinking … … PC, laptop, PDA ?? ARULKUMAR V - AP/CSE SECE
How many computers … in your house? – PC – TV, VCR, DVD, HiFi, cable/satellite TV – microwave, cooker, washing machine – central heating – security system can you think of more? in your pockets? – PDA – phone, camera – smart card, card with magnetic strip? – electronic car key – USB memory try your pockets and bags ARULKUMAR V - AP/CSE SECE
Interactivity? Long ago in a galaxy far away … batch processing – punched card stacks or large data files prepared – long wait …. – line printer output … and if it is not right … Now most computing is interactive – rapid feedback – the user in control (most of the time) – doing rather than thinking … Is faster always better? ARULKUMAR V - AP/CSE SECE
Richer interaction sensors and devices everywhere ARULKUMAR V - AP/CSE SECE
text entry devices keyboards (QWERTY et al.) chord keyboards, phone pads handwriting, speech ARULKUMAR V - AP/CSE SECE
Keyboards • 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 ARULKUMAR V - AP/CSE SECE
layout – QWERTY • Standardised layout but … – non-alphanumeric keys are placed differently – accented symbols needed for different scripts – minor 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. ARULKUMAR V - AP/CSE SECE
QWERTY (ctd) 2 3 4 5 6 7 8 9 0 Q W E R T Y U I 1 O P S D F H J LA G K Z X C V B N M , . SPACE ARULKUMAR V - AP/CSE SECE
alternative keyboard layouts Alphabetic – keys arranged in alphabetic order – not faster for trained typists – not faster for beginners either! Dvorak – 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 ARULKUMAR V - AP/CSE SECE
special keyboards • designs to reduce fatigue for RSI • for one handed use e.g. the Maltron left-handed keyboard ARULKUMAR V - AP/CSE SECE
Chord keyboards 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 ARULKUMAR V - AP/CSE SECE
phone pad and T9 entry • 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]555666 surprisingly fast! • T9 predictive entry – type as if single key for each letter – use dictionary to ‘guess’ the right word – hello = 43556 … – but 26 -> menu ‘am’ or ‘an’ ARULKUMAR V - AP/CSE SECE
Handwriting recognition • 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! ARULKUMAR V - AP/CSE SECE
Speech recognition • 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 ARULKUMAR V - AP/CSE SECE
Numeric keypads • for entering numbers quickly: – calculator, PC keyboard • for telephones not the same!! ATM like phone 4 5 6 7 8 9 * 0 # 1 2 3 4 5 6 1 2 3 0 . = 7 8 9 telephone calculator ARULKUMAR V - AP/CSE SECE
positioning, pointing and drawing mouse, touchpad trackballs, joysticks etc. touch screens, tablets eyegaze, cursors ARULKUMAR V - AP/CSE SECE
the Mouse • 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.) ARULKUMAR V - AP/CSE SECE
the mouse (ctd) Mouse located on desktop – requires physical space – no arm fatigue Relative movement only is detectable. Movement of mouse moves screen cursor Screen cursor oriented in (x, y) plane, mouse movement in (x, z) plane … … an indirect manipulation device. – device itself doesn’t obscure screen, is accurate and fast. – hand-eye coordination problems for novice users ARULKUMAR V - AP/CSE SECE
How does it work? Two methods for detecting motion • Mechanical – Ball on underside of mouse turns as mouse is moved – Rotates orthogonal potentiometers – Can be used on almost any flat surface • Optical – 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 ARULKUMAR V - AP/CSE SECE
Even by foot … • some experiments with the footmouse – controlling mouse movement with feet … – not very common :-) • but foot controls are common elsewhere: – car pedals – sewing machine speed control – organ and piano pedals ARULKUMAR V - AP/CSE SECE
Touchpad • 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 ARULKUMAR V - AP/CSE SECE
Trackball and thumbwheels Trackball – 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. Thumbwheels … – for accurate CAD – two dials for X-Y cursor position – for fast scrolling – single dial on mouse ARULKUMAR V - AP/CSE SECE
Joystick and keyboard nipple 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 ARULKUMAR V - AP/CSE SECE
Touch-sensitive screen • Detect the presence of finger or stylus on the screen. – works by interrupting matrix of light beams, capacitance changes or ultrasonic reflections – direct pointing device • Advantages: – fast, and requires no specialised pointer – good for menu selection – suitable for use in hostile environment: clean and safe from damage. • Disadvantages: – 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 ARULKUMAR V - AP/CSE SECE
Stylus and light pen Stylus – 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 Light Pen – now rarely used – uses light from screen to detect location BOTH … – very direct and obvious to use – but can obscure screen ARULKUMAR V - AP/CSE SECE
Digitizing tablet • Mouse like-device with cross hairs • used on special surface - rather like stylus • very accurate - used for digitizing maps ARULKUMAR V - AP/CSE SECE
Eyegaze • 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 ARULKUMAR V - AP/CSE SECE
Cursor keys • Four 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 ARULKUMAR V - AP/CSE SECE
Discrete positioning controls • in phones, TV controls etc. – cursor pads or mini-joysticks – discrete left-right, up-down – mainly for menu selection ARULKUMAR V - AP/CSE SECE
display devices bitmap screens (CRT & LCD) large & situated displays digital paper ARULKUMAR V - AP/CSE SECE
bitmap displays • screen is vast number of coloured dots ARULKUMAR V - AP/CSE SECE
resolution and colour depth • Resolution … used (inconsistently) for – 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 • Aspect ratio – ration between width and height – 4:3 for most screens, 16:9 for wide-screen TV • Colour depth: – 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 ARULKUMAR V - AP/CSE SECE
anti-aliasing 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 ARULKUMAR V - AP/CSE SECE
Cathode ray tube • 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 electron beam phosphor- coated screenARULKUMAR V - AP/CSE SECE
Health hazards of CRT ! • 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). ARULKUMAR V - AP/CSE SECE
Health hints … • do not sit too close to the screen • do not use very small fonts • do not look at the screen for long periods without a break • do not place the screen directly in front of a bright window • work in well-lit surroundings  Take extra care if pregnant. but also posture, ergonomics, stress ARULKUMAR V - AP/CSE SECE
Liquid crystal displays • 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 ARULKUMAR V - AP/CSE SECE
special displays Random Scan (Directed-beam refresh, vector display) – draw the lines to be displayed directly – no jaggies – lines need to be constantly redrawn – rarely used except in special instruments Direct view storage tube (DVST) – Similar to random scan but persistent => no flicker – Can be incrementally updated but not selectively erased – Used in analogue storage oscilloscopes ARULKUMAR V - AP/CSE SECE
large displays • 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 ARULKUMAR V - AP/CSE SECE
situated displays • 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 ARULKUMAR V - AP/CSE SECE
• small displays beside office doors • handwritten notes left using stylus • office owner reads notes using web interface Hermes a situated display small displays beside office doors handwritten notes left using stylus office owner reads notes using web interfaceARULKUMAR V - AP/CSE SECE
Digital paper • what? – thin flexible sheets – updated electronically – but retain display • how? – small spheres turned – or channels with coloured liquid and contrasting spheres – rapidly developing area appearance cross section ARULKUMAR V - AP/CSE SECE
virtual reality and 3D interaction positioning in 3D space moving and grasping seeing 3D (helmets and caves) ARULKUMAR V - AP/CSE SECE
positioning in 3D space • cockpit and virtual controls – steering wheels, knobs and dials … just like real! • the 3D mouse – six-degrees of movement: x, y, z + roll, pitch, yaw • data glove – fibre optics used to detect finger position • VR helmets – detect head motion and possibly eye gaze • whole body tracking – accelerometers strapped to limbs or reflective dots and video processing ARULKUMAR V - AP/CSE SECE
pitch, yaw and roll pitch yaw roll ARULKUMAR V - AP/CSE SECE
3D displays • 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. also see extra slides on 3D vision ARULKUMAR V - AP/CSE SECE
VR headsets • small TV screen for each eye • slightly different angles • 3D effect ARULKUMAR V - AP/CSE SECE
VR motion sickness • 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 ARULKUMAR V - AP/CSE SECE
simulators and VR caves • scenes projected on walls • realistic environment • hydraulic rams! • real controls • other people ARULKUMAR V - AP/CSE SECE
physical controls, sensors etc. special displays and gauges sound, touch, feel, smell physical controls environmental and bio-sensing ARULKUMAR V - AP/CSE SECE
dedicated displays • analogue representations: – dials, gauges, lights, etc. • digital displays: – small LCD screens, LED lights, etc. • head-up displays – found in aircraft cockpits – show most important controls … depending on context ARULKUMAR V - AP/CSE SECE
Sounds • beeps, bongs, clonks, whistles and whirrs • used for error indications • confirmation of actions e.g. keyclick also see chapter 10 ARULKUMAR V - AP/CSE SECE
Touch, feel, smell • 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 ARULKUMAR V - AP/CSE SECE
BMW iDrive • for controlling menus • feel small ‘bumps’ for each item • makes it easier to select options by feel • uses haptic technology from Immersion Corp. ARULKUMAR V - AP/CSE SECE
physical controls • specialist controls needed … – industrial controls, consumer products, etc. large buttons clear dials tiny buttons multi-function control easy-clean smooth buttons ARULKUMAR V - AP/CSE SECE
Environment and bio-sensing • 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 ARULKUMAR V - AP/CSE SECE
paper: printing and scanning print technology fonts, page description, WYSIWYG scanning, OCR ARULKUMAR V - AP/CSE SECE
Printing • 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!! ARULKUMAR V - AP/CSE SECE
Types of dot-based printers • dot-matrix printers – use inked ribbon (like a typewriter – line of pins that can strike the ribbon, dotting the paper. – typical resolution 80-120 dpi • ink-jet and bubble-jet printers – tiny blobs of ink sent from print head to paper – typically 300 dpi or better . • laser printer – 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. ARULKUMAR V - AP/CSE SECE
Printing in the workplace • shop tills – dot matrix – same print head used for several paper rolls – may also print cheques • thermal printers – special heat-sensitive paper – paper heated by pins makes a dot – poor quality, but simple & low maintenance – used in some fax machines ARULKUMAR V - AP/CSE SECE
Fonts • Font – the particular style of text Courier font Helvetica font Palatino font Times Roman font ∀ ♣×∝≡↵ℜ⊗↵∼ (special symbol) • Size of a font measured in points (1 pt about 1/72”) (vaguely) related to its height This is ten point Helvetica This is twelve point This is fourteen point This is eighteen point and this is twenty-four point ARULKUMAR V - AP/CSE SECE
Fonts (ctd) Pitch – 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” Serif or Sans-serif – sans-serif – square-ended strokes e.g. Helvetica – serif – with splayed ends (such as) e.g. Times Roman or Palatino ARULKUMAR V - AP/CSE SECE
Readability of text • lowercase – easy to read shape of words • UPPERCASE – better for individual letters and non-words e.g. flight numbers: BA793 vs. ba793 • serif fonts – helps your eye on long lines of printed text – but sans serif often better on screen ARULKUMAR V - AP/CSE SECE
Page Description Languages • 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 ARULKUMAR V - AP/CSE SECE
Screen and page • 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 ARULKUMAR V - AP/CSE SECE
Scanners • 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 ARULKUMAR V - AP/CSE SECE
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 ARULKUMAR V - AP/CSE SECE
Optical character recognition • 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 ARULKUMAR V - AP/CSE SECE
Paper-based interaction • 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 ARULKUMAR V - AP/CSE SECE
memory short term and long term speed, capacity, compression formats, access ARULKUMAR V - AP/CSE SECE
Short-term Memory - RAM • 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 ARULKUMAR V - AP/CSE SECE
Long-term Memory - disks • 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 ARULKUMAR V - AP/CSE SECE
Blurring boundaries • 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 ARULKUMAR V - AP/CSE SECE
speed and capacity • 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) ARULKUMAR V - AP/CSE SECE
virtual memory • 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 ARULKUMAR V - AP/CSE SECE
Compression • 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 ARULKUMAR V - AP/CSE SECE
Storage formats - text • ASCII - 7-bit binary code for to each letter and character • UTF-8 - 8-bit encoding of 16 bit character set • RTF (rich text format) - text plus formatting and layout information • SGML (standardized generalised markup language) - documents regarded as structured objects • XML (extended markup language) - simpler version of SGML for web applications ARULKUMAR V - AP/CSE SECE
Storage formats - media • Images: – many storage formats : (PostScript, GIFF, JPEG, TIFF, PICT, etc.) – plus different compression techniques (to reduce their storage requirements) • Audio/Video – again lots of formats : (QuickTime, MPEG, WAV, etc.) – compression even more important – also ‘streaming’ formats for network delivery ARULKUMAR V - AP/CSE SECE
methods of access • 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!! ARULKUMAR V - AP/CSE SECE
processing and networks finite speed (but also Moore’s law) limits of interaction networked computing ARULKUMAR V - AP/CSE SECE
Finite processing speed • 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 ARULKUMAR V - AP/CSE SECE
Moore’s law • 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! /e3/online/moores-law/ARULKUMAR V - AP/CSE SECE
the myth of the infinitely fast machine • 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 ARULKUMAR V - AP/CSE SECE
Limitations on interactive performance Computation bound – Computation takes ages, causing frustration for the user Storage channel bound – Bottleneck in transference of data from disk to memory Graphics bound – Common bottleneck: updating displays requires a lot of effort - sometimes helped by adding a graphics co- processor optimised to take on the burden Network capacity – Many computers networked - shared resources and files, access to printers etc. - but interactive performance can be reduced by slow network speed ARULKUMAR V - AP/CSE SECE
Networked computing 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 ARULKUMAR V - AP/CSE SECE
The internet • history … – 1969: DARPANET US DoD, 4 sites – 1971: 23; 1984: 1000; 1989: 10000 • common language (protocols): – TCP – Transmission Control protocol • lower level, packets (like letters) between machines – IP – Internet Protocol • reliable channel (like phone call) between programs on machines – email, HTTP, all build on top of these ARULKUMAR V - AP/CSE SECE

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In this document
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Overview of Chapter 2 on computers by Arulkumar V.

Elements of computer systems: input/output devices, memory, processing, network interaction.

Importance of understanding computer behavior for effective human-computer interaction.

Description of typical computer systems including devices that influence interaction modes.

Survey on the number of computers in homes and pockets including diverse devices.

Transition from batch processing to interactive computing, emphasizing user control and feedback.

Integration of sensors and devices for enhanced user interactions.

Overview of various text entry devices: keyboards, layout issues, and typing efficiency.

Discussion on alternative keyboard layouts and designs catering to specific needs.

Text entry methods using phone pads, handwriting recognition, and issues faced in usage.

Speech recognition advancements and numeric keypad usage for swift number entry.

Description of various input devices for positioning information on screens.

Use of foot-mouse and foot controls in specialized settings.

Details on touchpads, trackballs, and joysticks as input devices.

Functionality of touch-sensitive screens and digitizing tablets for precise control.

Eyegaze technology enabling hands-free control through gaze direction.

Cursor keys and discrete controls in various applications, including displays.

Explanation of bitmap displays, resolution, and color depth in various screens.

Anti-aliasing concepts, CRT functioning, and associated health hazards.

Liquid crystal displays benefits and functions in various electronic devices.

Discussion on random scan displays, large display systems, and their uses.

Introduction to digital paper concepts including flexible, electronically updated sheets.

Exploring positioning in 3D space and interaction experiences in virtual environments.

Methods for achieving accurate 3D controls and measurements in VR setups.

Different ways of visualizing 3D environments and associated motion sickness issues.

Usage of physical controls, haptics, and sound feedback in interaction design.

Haptic feedback technology in product designs for enhanced user experience.

Various environmental and bio-sensing technologies enhancing interaction.

Overview of printing mechanisms and OCR methods for paper-based interactions.

Discussion on font types, readability, and associated printing concepts.

Introduction to page description languages and WYSIWYG's impact on printing.

Different types of scanners and their applications in document processing.

Functionality of OCR technologies in converting images back to text.

Exploration of paper as an input and output medium through various technologies.

Types of memory in computing: RAM and its characteristics for performance.

Description of long-term storage options: magnetic disks and optical media.

Blurring boundaries in memory technologies including PDAs and flash memory.

Understanding speed and storage requirements alongside data compression techniques.

Examine various storage formats for text and media.

Methods for accessing large datasets through indexing and retrieval technologies.

Challenges in processing speed, limitations, and networked computing impacts.

The computer HCI

  • 1.
  • 2.
    The Computer a computersystem is made up of various elements each of these elements affects the interaction – input devices – text entry and pointing – output devices – screen (small&large), digital paper – virtual reality – special interaction and display devices – physical interaction – e.g. sound, haptic, bio-sensing – paper – as output (print) and input (scan) – memory – RAM & permanent media, capacity & access – processing – speed of processing, networks ARULKUMAR V - AP/CSE SECE
  • 3.
    Interacting with computers tounderstand human–computer interaction … need to understand computers! what goes in and out devices, paper, sensors, etc. what can it do? memory, processing, networks ARULKUMAR V - AP/CSE SECE
  • 4.
    A ‘typical’ computersystem • screen, or monitor, on which there are windows • keyboard • mouse/trackpad • variations – desktop – laptop – PDA the devices dictate the styles of interaction that the system supports If we use different devices, then the interface will support a different style of interaction window 1 window 2 12-37pm ? ARULKUMAR V - AP/CSE SECE
  • 5.
    How many … •computers in your house? – hands up, … … none, 1, 2 , 3, more!! • computers in your pockets? are you thinking … … PC, laptop, PDA ?? ARULKUMAR V - AP/CSE SECE
  • 6.
    How many computers… in your house? – PC – TV, VCR, DVD, HiFi, cable/satellite TV – microwave, cooker, washing machine – central heating – security system can you think of more? in your pockets? – PDA – phone, camera – smart card, card with magnetic strip? – electronic car key – USB memory try your pockets and bags ARULKUMAR V - AP/CSE SECE
  • 7.
    Interactivity? Long ago ina galaxy far away … batch processing – punched card stacks or large data files prepared – long wait …. – line printer output … and if it is not right … Now most computing is interactive – rapid feedback – the user in control (most of the time) – doing rather than thinking … Is faster always better? ARULKUMAR V - AP/CSE SECE
  • 8.
  • 9.
    text entry devices keyboards(QWERTY et al.) chord keyboards, phone pads handwriting, speech ARULKUMAR V - AP/CSE SECE
  • 10.
    Keyboards • Most commontext 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 ARULKUMAR V - AP/CSE SECE
  • 11.
    layout – QWERTY •Standardised layout but … – non-alphanumeric keys are placed differently – accented symbols needed for different scripts – minor 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. ARULKUMAR V - AP/CSE SECE
  • 12.
    QWERTY (ctd) 2 34 5 6 7 8 9 0 Q W E R T Y U I 1 O P S D F H J LA G K Z X C V B N M , . SPACE ARULKUMAR V - AP/CSE SECE
  • 13.
    alternative keyboard layouts Alphabetic –keys arranged in alphabetic order – not faster for trained typists – not faster for beginners either! Dvorak – 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 ARULKUMAR V - AP/CSE SECE
  • 14.
    special keyboards • designsto reduce fatigue for RSI • for one handed use e.g. the Maltron left-handed keyboard ARULKUMAR V - AP/CSE SECE
  • 15.
    Chord keyboards only afew 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 ARULKUMAR V - AP/CSE SECE
  • 16.
    phone pad andT9 entry • 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]555666 surprisingly fast! • T9 predictive entry – type as if single key for each letter – use dictionary to ‘guess’ the right word – hello = 43556 … – but 26 -> menu ‘am’ or ‘an’ ARULKUMAR V - AP/CSE SECE
  • 17.
    Handwriting recognition • Textcan 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! ARULKUMAR V - AP/CSE SECE
  • 18.
    Speech recognition • Improvingrapidly • 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 ARULKUMAR V - AP/CSE SECE
  • 19.
    Numeric keypads • forentering numbers quickly: – calculator, PC keyboard • for telephones not the same!! ATM like phone 4 5 6 7 8 9 * 0 # 1 2 3 4 5 6 1 2 3 0 . = 7 8 9 telephone calculator ARULKUMAR V - AP/CSE SECE
  • 20.
    positioning, pointing anddrawing mouse, touchpad trackballs, joysticks etc. touch screens, tablets eyegaze, cursors ARULKUMAR V - AP/CSE SECE
  • 21.
    the Mouse • Handheldpointing 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.) ARULKUMAR V - AP/CSE SECE
  • 22.
    the mouse (ctd) Mouselocated on desktop – requires physical space – no arm fatigue Relative movement only is detectable. Movement of mouse moves screen cursor Screen cursor oriented in (x, y) plane, mouse movement in (x, z) plane … … an indirect manipulation device. – device itself doesn’t obscure screen, is accurate and fast. – hand-eye coordination problems for novice users ARULKUMAR V - AP/CSE SECE
  • 23.
    How does itwork? Two methods for detecting motion • Mechanical – Ball on underside of mouse turns as mouse is moved – Rotates orthogonal potentiometers – Can be used on almost any flat surface • Optical – 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 ARULKUMAR V - AP/CSE SECE
  • 24.
    Even by foot… • some experiments with the footmouse – controlling mouse movement with feet … – not very common :-) • but foot controls are common elsewhere: – car pedals – sewing machine speed control – organ and piano pedals ARULKUMAR V - AP/CSE SECE
  • 25.
    Touchpad • small touchsensitive 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 ARULKUMAR V - AP/CSE SECE
  • 26.
    Trackball and thumbwheels Trackball –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. Thumbwheels … – for accurate CAD – two dials for X-Y cursor position – for fast scrolling – single dial on mouse ARULKUMAR V - AP/CSE SECE
  • 27.
    Joystick and keyboardnipple 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 ARULKUMAR V - AP/CSE SECE
  • 28.
    Touch-sensitive screen • Detectthe presence of finger or stylus on the screen. – works by interrupting matrix of light beams, capacitance changes or ultrasonic reflections – direct pointing device • Advantages: – fast, and requires no specialised pointer – good for menu selection – suitable for use in hostile environment: clean and safe from damage. • Disadvantages: – 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 ARULKUMAR V - AP/CSE SECE
  • 29.
    Stylus and lightpen Stylus – 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 Light Pen – now rarely used – uses light from screen to detect location BOTH … – very direct and obvious to use – but can obscure screen ARULKUMAR V - AP/CSE SECE
  • 30.
    Digitizing tablet • Mouselike-device with cross hairs • used on special surface - rather like stylus • very accurate - used for digitizing maps ARULKUMAR V - AP/CSE SECE
  • 31.
    Eyegaze • control interfaceby 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 ARULKUMAR V - AP/CSE SECE
  • 32.
    Cursor keys • Fourkeys (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 ARULKUMAR V - AP/CSE SECE
  • 33.
    Discrete positioning controls •in phones, TV controls etc. – cursor pads or mini-joysticks – discrete left-right, up-down – mainly for menu selection ARULKUMAR V - AP/CSE SECE
  • 34.
    display devices bitmap screens(CRT & LCD) large & situated displays digital paper ARULKUMAR V - AP/CSE SECE
  • 35.
    bitmap displays • screenis vast number of coloured dots ARULKUMAR V - AP/CSE SECE
  • 36.
    resolution and colourdepth • Resolution … used (inconsistently) for – 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 • Aspect ratio – ration between width and height – 4:3 for most screens, 16:9 for wide-screen TV • Colour depth: – 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 ARULKUMAR V - AP/CSE SECE
  • 37.
    anti-aliasing Jaggies – diagonal linesthat have discontinuities in due to horizontal raster scan process. Anti-aliasing – softens edges by using shades of line colour – also used for text ARULKUMAR V - AP/CSE SECE
  • 38.
    Cathode ray tube •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 electron beam phosphor- coated screenARULKUMAR V - AP/CSE SECE
  • 39.
    Health hazards ofCRT ! • 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). ARULKUMAR V - AP/CSE SECE
  • 40.
    Health hints … •do not sit too close to the screen • do not use very small fonts • do not look at the screen for long periods without a break • do not place the screen directly in front of a bright window • work in well-lit surroundings  Take extra care if pregnant. but also posture, ergonomics, stress ARULKUMAR V - AP/CSE SECE
  • 41.
    Liquid crystal displays •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 ARULKUMAR V - AP/CSE SECE
  • 42.
    special displays Random Scan(Directed-beam refresh, vector display) – draw the lines to be displayed directly – no jaggies – lines need to be constantly redrawn – rarely used except in special instruments Direct view storage tube (DVST) – Similar to random scan but persistent => no flicker – Can be incrementally updated but not selectively erased – Used in analogue storage oscilloscopes ARULKUMAR V - AP/CSE SECE
  • 43.
    large displays • usedfor 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 ARULKUMAR V - AP/CSE SECE
  • 44.
    situated displays • displaysin ‘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 ARULKUMAR V - AP/CSE SECE
  • 45.
    • small displaysbeside office doors • handwritten notes left using stylus • office owner reads notes using web interface Hermes a situated display small displays beside office doors handwritten notes left using stylus office owner reads notes using web interfaceARULKUMAR V - AP/CSE SECE
  • 46.
    Digital paper • what? –thin flexible sheets – updated electronically – but retain display • how? – small spheres turned – or channels with coloured liquid and contrasting spheres – rapidly developing area appearance cross section ARULKUMAR V - AP/CSE SECE
  • 47.
    virtual reality and3D interaction positioning in 3D space moving and grasping seeing 3D (helmets and caves) ARULKUMAR V - AP/CSE SECE
  • 48.
    positioning in 3Dspace • cockpit and virtual controls – steering wheels, knobs and dials … just like real! • the 3D mouse – six-degrees of movement: x, y, z + roll, pitch, yaw • data glove – fibre optics used to detect finger position • VR helmets – detect head motion and possibly eye gaze • whole body tracking – accelerometers strapped to limbs or reflective dots and video processing ARULKUMAR V - AP/CSE SECE
  • 49.
    pitch, yaw androll pitch yaw roll ARULKUMAR V - AP/CSE SECE
  • 50.
    3D displays • desktopVR – 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. also see extra slides on 3D vision ARULKUMAR V - AP/CSE SECE
  • 51.
    VR headsets • smallTV screen for each eye • slightly different angles • 3D effect ARULKUMAR V - AP/CSE SECE
  • 52.
    VR motion sickness •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 ARULKUMAR V - AP/CSE SECE
  • 53.
    simulators and VRcaves • scenes projected on walls • realistic environment • hydraulic rams! • real controls • other people ARULKUMAR V - AP/CSE SECE
  • 54.
    physical controls, sensorsetc. special displays and gauges sound, touch, feel, smell physical controls environmental and bio-sensing ARULKUMAR V - AP/CSE SECE
  • 55.
    dedicated displays • analoguerepresentations: – dials, gauges, lights, etc. • digital displays: – small LCD screens, LED lights, etc. • head-up displays – found in aircraft cockpits – show most important controls … depending on context ARULKUMAR V - AP/CSE SECE
  • 56.
    Sounds • beeps, bongs,clonks, whistles and whirrs • used for error indications • confirmation of actions e.g. keyclick also see chapter 10 ARULKUMAR V - AP/CSE SECE
  • 57.
    Touch, feel, smell •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 ARULKUMAR V - AP/CSE SECE
  • 58.
    BMW iDrive • forcontrolling menus • feel small ‘bumps’ for each item • makes it easier to select options by feel • uses haptic technology from Immersion Corp. ARULKUMAR V - AP/CSE SECE
  • 59.
    physical controls • specialistcontrols needed … – industrial controls, consumer products, etc. large buttons clear dials tiny buttons multi-function control easy-clean smooth buttons ARULKUMAR V - AP/CSE SECE
  • 60.
    Environment and bio-sensing •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 ARULKUMAR V - AP/CSE SECE
  • 61.
    paper: printing andscanning print technology fonts, page description, WYSIWYG scanning, OCR ARULKUMAR V - AP/CSE SECE
  • 62.
    Printing • image madefrom 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!! ARULKUMAR V - AP/CSE SECE
  • 63.
    Types of dot-basedprinters • dot-matrix printers – use inked ribbon (like a typewriter – line of pins that can strike the ribbon, dotting the paper. – typical resolution 80-120 dpi • ink-jet and bubble-jet printers – tiny blobs of ink sent from print head to paper – typically 300 dpi or better . • laser printer – 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. ARULKUMAR V - AP/CSE SECE
  • 64.
    Printing in theworkplace • shop tills – dot matrix – same print head used for several paper rolls – may also print cheques • thermal printers – special heat-sensitive paper – paper heated by pins makes a dot – poor quality, but simple & low maintenance – used in some fax machines ARULKUMAR V - AP/CSE SECE
  • 65.
    Fonts • Font –the particular style of text Courier font Helvetica font Palatino font Times Roman font ∀ ♣×∝≡↵ℜ⊗↵∼ (special symbol) • Size of a font measured in points (1 pt about 1/72”) (vaguely) related to its height This is ten point Helvetica This is twelve point This is fourteen point This is eighteen point and this is twenty-four point ARULKUMAR V - AP/CSE SECE
  • 66.
    Fonts (ctd) Pitch – 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” Serif or Sans-serif – sans-serif – square-ended strokes e.g. Helvetica – serif – with splayed ends (such as) e.g. Times Roman or Palatino ARULKUMAR V - AP/CSE SECE
  • 67.
    Readability of text •lowercase – easy to read shape of words • UPPERCASE – better for individual letters and non-words e.g. flight numbers: BA793 vs. ba793 • serif fonts – helps your eye on long lines of printed text – but sans serif often better on screen ARULKUMAR V - AP/CSE SECE
  • 68.
    Page Description Languages •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 ARULKUMAR V - AP/CSE SECE
  • 69.
    Screen and page •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 ARULKUMAR V - AP/CSE SECE
  • 70.
    Scanners • Take paperand 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 ARULKUMAR V - AP/CSE SECE
  • 71.
    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 ARULKUMAR V - AP/CSE SECE
  • 72.
    Optical character recognition •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 ARULKUMAR V - AP/CSE SECE
  • 73.
    Paper-based interaction • paperusually 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 ARULKUMAR V - AP/CSE SECE
  • 74.
    memory short term andlong term speed, capacity, compression formats, access ARULKUMAR V - AP/CSE SECE
  • 75.
    Short-term Memory -RAM • 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 ARULKUMAR V - AP/CSE SECE
  • 76.
    Long-term Memory -disks • 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 ARULKUMAR V - AP/CSE SECE
  • 77.
    Blurring boundaries • 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 ARULKUMAR V - AP/CSE SECE
  • 78.
    speed and capacity •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) ARULKUMAR V - AP/CSE SECE
  • 79.
    virtual memory • 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 ARULKUMAR V - AP/CSE SECE
  • 80.
    Compression • reduce amountof 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 ARULKUMAR V - AP/CSE SECE
  • 81.
    Storage formats -text • ASCII - 7-bit binary code for to each letter and character • UTF-8 - 8-bit encoding of 16 bit character set • RTF (rich text format) - text plus formatting and layout information • SGML (standardized generalised markup language) - documents regarded as structured objects • XML (extended markup language) - simpler version of SGML for web applications ARULKUMAR V - AP/CSE SECE
  • 82.
    Storage formats -media • Images: – many storage formats : (PostScript, GIFF, JPEG, TIFF, PICT, etc.) – plus different compression techniques (to reduce their storage requirements) • Audio/Video – again lots of formats : (QuickTime, MPEG, WAV, etc.) – compression even more important – also ‘streaming’ formats for network delivery ARULKUMAR V - AP/CSE SECE
  • 83.
    methods of access •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!! ARULKUMAR V - AP/CSE SECE
  • 84.
    processing and networks finitespeed (but also Moore’s law) limits of interaction networked computing ARULKUMAR V - AP/CSE SECE
  • 85.
    Finite processing speed •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 ARULKUMAR V - AP/CSE SECE
  • 86.
    Moore’s law • computersget 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! /e3/online/moores-law/ARULKUMAR V - AP/CSE SECE
  • 87.
    the myth ofthe infinitely fast machine • 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 ARULKUMAR V - AP/CSE SECE
  • 88.
    Limitations on interactive performance Computationbound – Computation takes ages, causing frustration for the user Storage channel bound – Bottleneck in transference of data from disk to memory Graphics bound – Common bottleneck: updating displays requires a lot of effort - sometimes helped by adding a graphics co- processor optimised to take on the burden Network capacity – Many computers networked - shared resources and files, access to printers etc. - but interactive performance can be reduced by slow network speed ARULKUMAR V - AP/CSE SECE
  • 89.
    Networked computing Networks allowaccess 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 ARULKUMAR V - AP/CSE SECE
  • 90.
    The internet • history… – 1969: DARPANET US DoD, 4 sites – 1971: 23; 1984: 1000; 1989: 10000 • common language (protocols): – TCP – Transmission Control protocol • lower level, packets (like letters) between machines – IP – Internet Protocol • reliable channel (like phone call) between programs on machines – email, HTTP, all build on top of these ARULKUMAR V - AP/CSE SECE