Part D - Computers


Describe the Devices that transfer information to and from computers

Character Entry | Display | Printing | Pointing | Physical | Exercises

The devices that we use to communicate with computers have evolved less rapidly than the internal computing technology itself.  Many of the devices originally introduced have survived in some slightly modified form.  Many refinements have been in the details rather than the architecture itself.  We still use keyboards, view displays, and make hard copies on printers.  Keyboards, displays, and printers still serve as the principal communication devices and their footprints have remained about the same.  Of course, other input and output devices have been developed and some have established a lasting foothold alongside keyboards, displays, and printers. 

In this chapter, we survey the principal communication devices for inputting information into computers and outputting information from computers.  We then review devices that provide more direct communication with the physical world.

Character Entry Devices

The most common method of entering characters into computers has always been through keyboards.  The character entry devices in use today include

  • standard keyboards
    • alphanumeric keyboards
    • chorded keyboards
  • numeric keypads
  • thumbpads

Standard Keyboards

The standard keyboards are all based on well-established and refined designs imported directly into the field of computing.  The original sources include typewriter, telegraph, telephone, and calculator technologies. 

IBM Alphanumeric Keyboards

The first standard keyboard for personal computers was developed by IBM.  The original keyboard had 83 keys.  The enhanced version, with a numeric keypad, had 101 keys:

ibm keyboard
IBM Keyboard (source: Mysid Wikipedia 2008 CC-BY-SA)

The popular version has two system keys and an application key, which brings the number of keys to 104:

ibm keyboard
IBM Keyboard (source: Mysid Wikipedia 2008 CC-BY-SA)

Note the location of the modifier keys:

  • Control key
  • Shift key
  • Alt key

Microsoft adopted this keyboard as the basis for its Windows version.

Apple Alphanumeric Keyboards

The keyboard layout for Apple's MacBook differs slightly from the standard IBM layout. 

apple keyboard
Apple Keyboard (source: roadmr Wikipedia 2006 CC-BY-SA)

Note the different location of the modifier keys on this keyboard.  The Command and Option keys are reversed on this keyboard compared to their counterparts on the Windows keyboards (these are the Windows System and Alt keys respectively). 

apple modifier keys
Apple Modifier Keys (source: benhalsall Wikipedia 2006 CC-BY)

The Windows keypad, scroll lock, and print screen keys on the MacBook keyboard running Bootcamp are as follows:

  • Print Screen - Fn + Shift + F11
  • Alt + Print Screen - Fn + Shift + Alt + F11
  • Scroll Lock - Fn + Shift + F12
  • Home - Fn + Left
  • End - Fn + Right
  • PgUp - Fn + Up
  • PgDn - Fn + Down
  • Delete - Fn + delete
  • Insert - no equivalent
  • Backspace - delete
  • Pause/Break - no equivalent

To obtain the complete Windows keyboard on a MacBook running Bootcamp, you can access the on-screen keyboard through the Windows command line utility 'osk'.


The key layout on both IBM and Apple keyboards is the QWERTY layout inherited from typewriter technology.  The term QWERTY stands for the keys in the top row just below the numeric row.  This layout was patented by Christopher Scholes in 1874 and sold to Remington in the same year. 

old hermes typewriter
Typewriter (source: Wikipedia 2009 PD)

The QWERTY layout avoids key jams during rapid typing.  Key jams were a dominant obstacle to the improvement of typing speeds.  The QWERTY layout places the most commonly used letters well-separated from each other:

Reason for QWERTY (source: Wikipedia 2008 PD)

104-key US QWERTY Keyboard (source: Mysid Wikipedia 2005 CC-BY-SA)

Dvorak Layout

The Dvorak layout is a viable alternative to the QWERTY layout.  August Dvorak and William Dealey patented this layout in 1936.  They designed it to minimize finger motion, in order to increase typing rate and reduce errors:

Dvorak Simplified Keyboard (source: StartBrady Wikipedia 2006 CC-BY-SA)

Virtual Keyboards

There are a numerous virtual keyboards available on the Internet.  Consider the following one from Scientec.

Chinese Keyboard

Virtual keyboards that help construct Chinese characters are in the modern operating systems.  These keyboards are QWERTY like with symbols for standard sets of character.  Typing the symbol displays a set of possible character from which to select.  Selecting one of those characters transfers it to the character display area. 

For example, try this virtual keyboard from

Chorded Keyboards

An average typist can type between 50 and 80 words per minute on a standard alphanumeric keyboard.  Chorded keyboards use a combination of key presses to represent a single key.  They are specialized keyboards designed for stenographers, court reporters, and closed captioners who must type at speeds in the order of 200 words per minute:

Stenotyper - Chorded Keyboard (source: Osukarojo Wikipedia 2008 PD)

Finger-Switch Keyboards

A common ailment arising from the prolonged use of computer keyboards is repetitive strain injury.  Many ergonomic solutions have been proposed to relieve this injury. 

The DataHand uses five-key switches around each finger tip:

(source: getDave Wikipedia 2006 PD)

YouTube Video Describing the DataHand

Numeric Keypads

Numeric keypads were designed primarily for numeric rather than alphanumeric input.  These keypads do not share a uniform layout.

The telephone and cell phone keypads have the 123 row as their top row

Telephone Keypad (source: Wagner Wikipedia 2008 CC_BY)

Calculator keypads have the 123 row as their bottom row

Calculator Keypad (source: Arpingstone Wikipedia 2007 PD)


Thumbpads differ from standard keyboards in their design.  The operator uses thumbs rather than all 10 fingers to type.  The typing speed is necessarily slower and the typing is more error prone:

Nokia Products Web Site

The Nokia and Blackberry have the same key layout except for the bottom row:

(source: ricardo/ Wikipedia 2008 CC-BY)

Display Devices

The most common form of reporting information from computers has been through display monitors.  The types of displays currently available include:

  • bitmapped displays
  • vector displays
  • projection displays
  • digital paper

Bitmapped Displays

Bitmapped displays use screens that consist of pixels arranged in a 2-dimensional array across the display surface.  Each pixel has a bit-depth.  An 8-bit pixel can display 256 different colours.  A 24-bit pixel can display 16,777,216 different colours.  We call the set of colours that a surface can display the colour map.  Typical bit-depths are 24 and 32. 

We describe the resolution of a bitmapped display in terms of the number of pixels and their density.  72 ppi and 96 ppi are common resolutions.  The actual resolution of a display depends upon the resolution sent by the system to the video card.  The specifications of a display report the maximum resolution and not necessarily the actual one. 

The types of bitmapped displays include:

  • Cathode Ray Tube (CRT)
  • Liquid Crystal Display (LCD)

CRT Displays

CRT displays evolved from traditional television displays.  In other words, a CRT monitor is television monitor with some enhanced properties.  CRT technology is well-developed, fast, and inexpensive. 

The screen of a CRT monitor has a phosphor coating and the monitor uses an electron beam to scan this coating.  The monitor creates its images by scanning the screen surface horizontally, line by line.  When the beam is on, the phosphor glows.  Colour monitors use three different phosphors.  A shadow mask focuses a single colour from the colour triple.  Color screen resolution is lower than monochrome because of the shadow mask technique used to display the colour of a pixel.

(source: Wikipedia 2009 PD)

A CRT monitor can change the size of its pixels.  Interlacing is a method used build the image in increasing degrees of detail. 

The refresh rate of a CRT is an important property.  Most CRTs operate at a vertical scan rate of 60Hz or over.  The flicker-fusion threshold determines the cutoff for holding continuous impressions of an image in sensory memory.  CRT monitors show flicker at refresh rates lower than 30Hz. 

Potential health risks associated with CRTs include:

  • X rays from the back
  • small amounts of UV and IR radiation from the phosphor
  • RF emissions and 16Hz sound
  • Electromagnetic fields

LCD Device

LCDs do not produce a light of their own.  They require some external light source to be visible.  Typically, this is a source situated behind the LCD panel itself.  An LCD panel consists of a layer of liquid crystal compressed between two plates.  The top plate is transparent and polarized.  The liquid crystal when subjected to voltage twists.  These twists change the properties of the light passing through the top layer.  The rate of twist is slow, so that generally there is no flicker. 

(source: Wikipedia 2009 PD)

The LCD cannot change the size of a pixel and adds a black border to compensate for any change in resolution. 

LCDs are less tiring than CRTs because of the reduced flicker.  LCDs also have lower emissions. 


Bitmapped displays use anti-aliasing to account for the discrete size of each pixel.  This technique modifies the image to give an illusion of smoothness.

(source: Wikipedia 2007 GNU Free)

Vector Display

Vector displays use graphics primitives to create images.  The primitives are based on mathematical formulas and are scalable without loss of accuracy.  Bitmap displays produce jaggies as shown below.  Vector displays don't produce jaggies.  A vector display produces accurate lines. 

Vector Display (source: Mahlum Wikipedia 2007 PD)

Vector displays are slow and prone to flicker. 

CRT Projectors

Projection displays project images onto a screen that is separate from the display itself.  A problem with these displays is that the shadow of the presenter can interfere with the projection.  One solution is back-projection where the display projects the image onto semi-frosted glass. 

Projection Display (source: KalW Wikipedia 2006 PD)

Digital Paper

Digital paper is an emerging technology that is writable and retains its contents when the power is disconnected.  It has potential for publication, large scale banners, and soft printouts. 

Amazon Kindle 2 (source: ShakataGaNai Wikipedia 2009 CC-BY-SA)

Here is an 3-minute video showing 28 new eReaders for 2010

Printing Devices

Many people still prefer to read from paper rather than from any display device.  Modern printers are quite capable of producing near-publication quality output at a relatively rapid rate. 

Two popular types of printers are:

  • laser printers
    • monochrome
    • colour
  • ink-jet printers

Laser printers are fast and inexpensive.  They produce:

  • high quality
  • poor graphics
  • maximum resolution of 1200 dpi

Ink-jet printers are slower and expensive.  They produce:

  • full color
  • photo quality graphics
  • maximum resolution of 1440 dpi

Pointing Devices

Many modern applications rely upon accurate pointing devices.  Pointing devices have been highly developed particularly in the field of Computer-Aided-Design (CAD).  They rely on a visible connection between a symbol on the display and the device itself.  With such devices, we can position and select any object that appears on a display. 

Cursor Keys

The original pointing device was the cursor with a set of dedicated cursor keys.  Cursor keys still represent a convenient, simple and popular alternative for selecting within a list of items.  There is no standard layout for these keys, although the inverse 'T' layout is qute common. 

(source: Wikipedia 2009 PD)


Currently, the most popular pointing device is the mouse.  A mouse typically has one or more buttons and moves the cursor on a screen indirectly.  The motion of the mouse and the cursor on the screen are both two-dimensional.  Some desk space is required to move the mouse, but it can be lifted to realign its reference position thereby keeping its footprint to a minimum.  Once we locate a position on the screen, pressing one of the buttons performs an application specific action on the object at that position.

(source: Darkone Wikipedia 2005 CC-BY-SA)


There are three types of mice:

  • roller
  • optical
  • foot

The roller mouse operates mechanically with the aid of a ball that remains in contact with the host surface.  This mouse requires cleaning dust and dirt from time to time off the rollers that touch the ball inside the mouse. 

The optical mouse is better than the roller mouse in the sense that it does not contain any rollers that need to be cleaned.  However, the optical mouse requires a reflective host surface.  It doesn't operate on a black surface.

The footmouse has been around for some time but has never caught on in the field of computing (compare, pedals in musical instruments).


The trackball is an upside down roller mouse.  We move the ball directly by finger or thumb.  Unlike surface mice, this device does not require any space on the desk around which to move. 

(source: Suimasentyottohensyuushimasuyo Wikipedia 2006 CC-BY-SA)

It is difficult to draw lines with a trackball, since finger and thumb movements must be used instead of arm movements.  Long distance movements are difficult to represent. 


A touchpad is similar to a trackball.  A touchpad has a relatively small area for finger travel.  The acceleration of the fingertip on the touchpad determines the speed of movement of the cursor on the screen, so that movement across an entire screen is accomplished in relatively few quick strokes.  The advantage of a touchpad is the absence of a need for a separate device - the touchpad is built-in.

(source: Wikipedia 2010)


The most common type of controller is a joystick.  The joystick can detect motion in two directions and twisting in the third direction.  Joysticks and the simpler extremely popular hand-held controllers are quite useful in gaming applications.  There are two types of joystick:

  • absolute - position of the stick determines the position on the screen
  • isometric - pressure determines the velocity of the cursor

Joysticks can incorporate force feedback to give the user confirmation and a richer gaming experience. 

(source: Jaworski Wikipedia 2007 CC-BY-SA)

Pointing Stick

The pointing stick is similar to a joystick.  It detects motion in two directions.  It has virtually no dead zone.

(source: Inklein Wikipedia 2009 CC-BY)

Touch Screen

The touch screen is much more direct than other pointing devices, such as mice, controllers, etc..  Touch screens have gained popularity with smartphones and tablet computers. 

A touch screen detects where the user has pressed the screen.  Touch screens are useful whereever it is inconvenient to place other input devices.  However, touch screens have limited resolution due to the relatively large size of the fingertip. 

Here is an 8-minute presentation by Jeff Han on Touch Screens at TED

Light Pen

The light pen provides fine selection capability with respect to areas on a screen. 

(source: Greg Lloyd Wikipedia 2005 CC-BY)

One difficulty with this type of pointing device is that the hand holding it tends to obscure the image being displayed.  The solution is to place the menus at the bottom of the screen and to have different layouts for right-handed and left-handed users. 

Physical Devices

Physical devices bypass the abstract stages of inter-computer communication such as character sets and provide more direct communication with the physical world.  These devices include:

  • scanners
  • digital cameras
  • digitizing tablets
  • speech recognizers
  • eyetrackers


Scanners optically scan physical images and convert them into digital ones.  These physical images may be photos, prints, text, scripts, or objects in general.  Scanners include flatbed models, drum models, hand-held models, and bar code readers.  Historically, their predecessors are telephotography and fax devices. 

High-end flatbed scanners can scan at resolutions up to 5400 pixels per inch (ppi), while drum scanners can scan at resolutions between 3000 and 24000 ppi.  Typical pixel depths with scanners are 24-bits. 

Scanners store images in a variety of formats including bitmaps and JPEG.  Bitmaps require very large file sizes.  JPEG is a method of compressing bitmaps in digital photgraphy that produces a considerably smaller file size with minimum loss in quality. 

As scanners have become more refined they have generated larger amounts of data, which has required faster and faster connections.  Modern scanners can communicate over parallel ports, scsi interfaces, usb ports, and firewire ports.

Script Conversion

Conversion of scripts into text may be

  • on-line
  • off-line

On-line conversion can distinguish between right-to-left and left-to-right gestures and is also called dynamic character recognition, real-time character recognition, and intelligent character recognition.

The most common form of off-line conversion is Optical Character Recognition (OCR).  OCR software can transform image files that contain scripts into text.  Such software requires calibration to specific fonts.  Recognition of Latin script is still not 100% and requires human review.  Recognition of other scripts is still in active research stages.

Digital Cameras

Digital cameras receive optical images and convert them into electronic signals using an image sensor.  These cameras use either

  • CCD - analog charge coupled device
  • CMOS - complementary metal oxide semiconductor pixel sensors

CCD is more susceptible to smear from bright light sources, CMOS is susceptible to rolling shutter effect. 

Digitizing Tablets

Digitizing tablets are input devices for tracing over existing images to digitize aspects of the images.  These tablets can serve as accurate pointing devices and be used where fine motion is important.  These tablets require a large amount of desk space.  There are three types:

  • resistive - detect contact between two sheets (without a pen)
  • magnetic - capture current pulses from a pen
  • sonic - adaptable to 3d - no special surface

(source: Matok Wikipedia 2006 CC-BY-SA)

Speech Recognizers

Speech recognition software converts audio signals into text.  Because narrative is highly interpretive, speech recognition often requires human review.  One area of application has been the health-care domain.  Other areas include aircraft and telephony. 

List of Speech Recognition Software

Speech Recognition Mascot (source: Wagner Wikipedia 2008 CC_BY)

Error rates on some speech recognition software are as low as 1%, while on others as high as 50%.  Progress is slow and difficult to measure in this field.


Eyetracking tracks eye movements.  Eyetrackers use a low power laser that reflects off the retina.  As the direction that the eye faces changes the reflection changes. 

Eyetrackers have been used in military applications and UI research.  This device is not suitable for drawing, since the eye does not move in straight lines.

(source: Wikipedia 2009 PD)

3-D Devices

Devices that operate in three dimensions are still in their infancy.  Much research needs to be done in this area.

Navigation in 3-dimensions involves selecting not only position but also orientation.  The shift from 2 dimensions to 3 dimensions is a shift from 2 degrees of freedom to 6 degrees of freedom. 

We measure changes in orientation with respect to a point ahead and along our line of sight

  • pitch - move the forward point up or down
  • yaw - move the forward point left or right
  • roll - rotate about the axis to the forward point

Recent shipments of virtual reality devices include:

3-D Mice

3-D mice generally function through ultrasound and provide three rather than two degrees of freedom.

Experiments on 3-D mice have included:

Problems with 3-d mice involving holding them steady in mid-air for any extended period of time.

Data Gloves

Data gloves capture hand movements.  Experiments on data gloves have included:

  • Nintendo's Power Glove - imprecise, difficult to use controls
  • CyberGlove - Lycra glove with optical fibres.  Can measure 10 joint angles and 3-d spatial information along with degree of wrist rotation.

Cyber Glove (source: Jayserinos99 Wikipedia 2009 CC-BY)

3-D Displays

The primary task of current 3-dimensional display devices is to create a sensation of depth for the viewer.  Devices distinguish into two categories:

  • multiple two-dimensional image devices
  • fully three-dimensional image devices

With multiple 2-D devices the viewer is restricted in their movement and the information available.

Multiple 2-Dimensional Displays

Traditional stereoscopic displays involve the user wearing special spectacles that polarize incoming light differently for each eye.

Autostereoscopic displays limit head positions and send different images to each eye.

Stereoscopic vision involves sending slightly different display data to each eye.  The lag between user initiative and system response can cause motion sickness.

3-Dimensional Displays

Volumetric displays consist of voxels (instead of pixels) and display points of light physically within a volume. 

Computer generated holographic displays create light fields that mimic the actual scene.  Currently, this involves too much computation to be practically viable. 

Here is a 1-minute video on Holograms