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Chapter 3 Objectives Explain how input and output devices
operate and integrate into a computer system
Explain why a typical computer has different types of storage devices and their purpose
Diagram how the components of a computer system fit together
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Input: Providing Data to the CPU (Processor)
Most users are unaware of a computer's internal information processing
User sees only input and output – "I/O." Early computer users had to flip
switches or plug wires into switchboards Today, users can choose from many
different input devices that make it easy to enter data and commands
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The Keyboard
Most familiar input device QWERTY keyboard dates back to
manual typewriters (but other formats available)
Typical keyboard sends signals to computer through cable—usually ASCII/Unicode via USB
Keyboards may be wireless (Bluetooth)
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Pointing Devices Mouse: Moves cursor Wireless mice: Use Bluetooth or other
wireless frequencies Touchpad: A flat panel, sensitive to touch and
pressure Trackpoint, trackball: Alternatives to mouse Graphics tablet: Flat panel for pen/stylus Game controllers: Specialised for games
(steering wheel, joy stick, game pad) Touch screen: Monitor sensitive to touch
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Multi-Touch Input Devices
Use more sophisticated pressure sensors to facilitate more complicated touch patterns
Touch-sensitive screen or trackpad can recognize position, pressure, contact area and movement of more than one contact point simultaneously
Best known example is Apple’s iPhone and iPad – recognize one and two fingered movements
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Reading Tools Devices allow computers to read
notations/markings that represent codes:› Optical mark readers› Magnetic ink character readers› Bar code readers› Radio frequency identification
(RFID) readers› Scanners and pen scanners
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Digitizing Devices and Sensors
Devices for capturing and converting information into a binary encoding› Scanners: Tools for static images› Cameras: Video and still photography› Microphones: Voice and sound› Environmental Sensors: Temperature,
humidity, moisture, acceleration, pressure, etc.
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Translators
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Devices for converting input from one format to another (data processing)
Speech recognition: Turning sound into text
Text recognition (OCR – Optical Character Recognition): Turning a pixel-based image into text (e.g., a scan into a Word Document)
Output: Observable Results
Output devices cause real-world effects that can be interpreted by humans or by other machines
Convert computer’s internal bit patterns into alternative formats
Output produced by various devices:› Display screens for immediate visual output› Printers for permanent paper output› Speakers for audio output› Haptic devices (vibrators in game pads)› Motors, relays, other mechanical devices
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Screen Output
Display: Also called a monitor Display size measured length of diagonal line
across screen Images composed of tiny dots called pixels
(PIcture ELementS) Resolution: Measured in dots per inch (dpi) Aspect ratio: Relationship between width
and height Monitors use liquid crystal digital (LCD)
technology11
Aspect Ratio
Relative Measure of Width to Height
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4:3
4:3
Image is made up of rows of colored pixels Pixels are extremely small and can’t be
easily distinguished Monitor’s image is refreshed 24+ times per
second Each pixel is made up of mixture of red,
green, blue By varying the brightness of the three
colors, a monitor can display millions of unique colors 13
Colour Display
Digitizing involves using an input device to take of tiny large numbers of tiny samples.
A representation of the original image can be reconstructed by assembling all samples in order
Digitization Quality:› Lossy – Some information (detail) is lost when it
is reconstructed (common with sampling)› Lossless – No information is lost during
reconstruction (rare, hard to do)
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Digitizing Information
Pixelization Pixels – PIcture ELementS – are formed
by cutting an image into tiny little squares and taking the average colour of each square
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Pixelation It looks "normal" if the squares are
really small If the squares are too big it looks grainy
or "blocky" – problem if "blown up" too much
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Colour Models RGB
› Red, Green, Blue› R + G + B = White› Used in monitors› Additive – adding colour to blank media (black)
CMYK› Cyan, Magenta, Yellow› Subtractive – subtracting colour from saturated
media (white)› Used in printers› Imperfections in ink cause C+M+Y to create a
muddy brown, so K (blacK) is used instead
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Most printers mix various amounts of cyan, magenta, yellow, and black pigments to create a color.
Matching on-screen color with printed color is difficult.
Monitors can display more colors than printers.
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Coloured Printing
Paper Output Impact printers: Form images by physically
striking paper, ribbon, and print hammer together Nonimpact printers: Generally replacing impact
printers› Laser printers: High-quality pages, quickly› Inkjet printers: Spray ink directly onto paper› Photo printers: Specialized inkjets print photos› Thermal: Require heat sensitive paper
Plotters: use a pen to draw maps, blueprints
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Fax Machines Facsimile (fax) machine: Scans page,
converts it to binary and sends it over phone lines to another fax machine
Receiving machine might just be a computer that uses its printer to create the document
Not really a current technology – phone lines and Internet are no longer cleanly separated
Fax machines are really just specialised printers these days
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Audio Output
Most PCs have some form of internal speaker› Produce simple system sounds
Sound output jacks for headphones, powered speakers, and other audio output devices› Higher quality sound production
Headphones are wearable speakers, headsets have a built-in microphone
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Controlling Other Machines
Many machines and systems are controlled by computers:› Robot arms› Telephone switchboards› Transportation devices› Automated factory
equipment› Spacecraft
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Storage Devices
Storage can be› Persistent: Data exists without power› Volatile: Data is lost when power is lost
Primary Storage: Computer "memory" is volatile and sometimes referred to as primary storage, even though it isn't meant for long term storage of data
Secondary Storage: Devices that are persistent are often referred to as secondary storage
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Storage Access
Sequential Access› Must start at beginning› Can't skip over data when reading › E.g., Tapes
Random Access› Can read anywhere on the device › E.g., Disk Drives
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Internal and External Drives
Hard disk drives and optical disk drives can be external or internal.› Internal drives: Reside inside casing of
computer and can't be removed PCs generally can have 4 at most
› External drives: Can be connected through USB or FireWire ports Relatively easy to transport between locations Can be shared between computers Slower access speeds compared to internal
drives26
Magnetic Tape
Tape drives: Common storage devices on most mainframe computers› Can store massive amounts of information
on magnetic tape in a small space at a relatively low cost
› Tape is sequential-access medium, so retrieving information is time consuming
Primarily used to back up or archive critical data
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Magnetic ("hard") Disks Magnetically coated surface stores
encoded information› Provide random access capability› Retrieve information rapidly › Consist of multiple platters divided into tracks
(rings) and sectors PCs include 1+ hard disks as main
storage device Older "floppy" disks and Zip disks have all
but disappeared28
Optical Discs
Use laser beams to read and write data Shiny surface with pits that stop laser reflecting Sensor reads laser reflection:
› Reflected = 1 › Not reflected (a pit) = 0
Transparent plastic disc surface protects shiny surface from physical damage
Access speeds are slower than for magnetic discs Often used to make backup copies or transport data as the
media can be removed from the computer Write in a spiral (sequential, one pass only on write) Writeable and rewritable discs don't last forever, they break
down and data can become unreadable in as little as 15 years
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CD Principles
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Optical Disc Types CD-ROM (compact disc—read-only memory) discs CD-RW drive: Read data from CD-ROMs; record
data onto CD-R and CD-RW discs› CD-R (compact disc-recordable)—write-once, read-
many› CD-RW (compact disc rewritable) erasable
Rewritable DVD drives: Commonplace in PCs today› Can read and write to CD and DVD media› Gradually being replaced by Blu-ray drives› Blu-ray: Uses blue laser that allows for smaller pits
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Disc Capacity
CD-ROM(read-onlyCD)
CD-RW
DVD-ROM
(read-onlyDVD)
DVD/RW
BD/ROM(read-only
Blu-ray)
BD/RW
700 MB 700 MB
4.7 GB (single-
layerdisc)
4.7 GB (single-
layerdisc)
27 GB (single-
layerdisc)
27 GB (single-
layerdisc)
9.4 GB(dual-layer disc)
9.4 GB(dual-layer disc)
50 GB(dual-layer disc)
50 GB(dual-layer disc)
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Flash Memory Storage Devices Flash memory:
› Persistent› Erasable (rewriteable)› Removable› Size/shape is marketing› More expensive than hard
disks Flash memory cards: Used
to store data in digital cameras and cell phones
USB flash drives: Store and transport data with devices having a USB port
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Choose equipment that’s ergonomically designed
Create a healthful workspace
Build flexibility into work environment
Protect your ears Rest your eyes
Let technology work for you
Stretch Listen to your body Don’t leave healthy
habits at home Seek help when you
need it
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Ergonomics (User Comfort)
The Computer System: The Sum of Its Parts
Four basic designs for personal computers:› Tower systems: Tall narrow boxes that
generally have more expansion slots and bays, bigger power supplies, more cooling
› Flat desktop systems: Designed to sit under the monitor like a platform ("Pizza Boxes")
› All-in-one systems: Combine the monitor and system unit into a single housing
› Laptop computers: Include all essential components in one compact unit
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Ports and Slots
Legacy ports (using old data speeds) are too slow for today’s needs:› There used to be special purpose parallel ports for printers and
serial ports for keyboards and mice USB (universal serial bus) transmits data faster:
› USB 1.0 data transmitted at approximately 11 Mbps› USB 2.0 has transfer rates of up to 480 Mbps› USB 3.0 has data transfer rate of more than 3 Gbps› USB can also power a device (5 volts)› 4 wires – Power, Power ground, Data, Data ground
Remember …› Serial ports send and receive data one bit at a time in
sequence› Parallel ports send and receive bits in groups
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Apple's Firewire
FireWire: A high-speed connection standard developed by Apple
Can move data between devices at:› 400 Mbps (original version)› 800 Mbps (newer FireWire 800)
FireWire allows multiple devices to be connected to the same port.
Also can supply power to peripherals so they don’t need an external power supply
Falling out of vogue, USB is faster, more commonly used
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Wireless Peripherals, Network Peripherals, and "The Cloud"
Wireless technology› Bluetooth, Wifi, Cellular, Satellite› Keyboards, mice, cameras, printers, networking
Computer networks› Fibre optic, Wired, Wireless (radio signal)› Communication between devices (computers,
phones, tablets, printers) Internet “cloud”
› Use of storage or processing on another computer in the network
› May be "free" or for a fee38
Communication Technologies
Blue Tooth: Low power, very short range wireless (2-3m) – Cell phone headsets
WiFi: Short range inter-computer wireless (30m) – Laptops, cell phones, printers
Cellular: Longer range wireless via land-based "tower" network
Satellite: Long range wireless via orbiting network transceivers
Ethernet: Cabled connections between computers (faster than wireless)
Fibre Optic: Glass cables with signals transmitted using light – very high speed communication
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Memory Hierarchy
Goes from small storage and fast access (expensive) to large storage and slow access (cheap)› Register: in a core, 64 bits each› L1/L2 Cache: in core, 64 KB, 256 KB› L3 Cache: in CPU, 2-20 MB--------- In CPU above … Outside CPU below ---------› L4 Cache: on motherboard, 128 MB› Main Memory: on motherboard, 8-32 GB--------- Volatile above … Persistent below ---------› Solid State Disk Drive: in computer, 16-256 GB› Hard Disk Drive: in computer, .5 to 2 TB--------- Fixed above … Removable/External below ---------› DVD/CD (Optical Drive): in computer, 4.7 GB+› USB Drives (Flash or External Hard Disk): 1 GB to 2 TB› Cloud Storage: on network, virtually infinite
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Chapter 3 Summary Peripherals allow computer to communicate with outside
world via input and output and store information for later use.
I/O devices do input and output. Bar code readers, optical mark readers, and magnetic
ink readers recognize and translate specially printed patterns and characters.
Scanners and digital cameras convert photographs, drawings, and other analog images to digital files.
Sound digitizers convert information from microphone and other external audio devices.
Sensors detect motion, temperature, pressure, and other characteristics.
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Chapter 3 Summary Storage devices can be persistent or
volatile Large capacity magnetic disks are most
common form of storage because of high-speed random access capability
Optical discs are most common removable storage media
Solid-state flash memory is replacing disks and tapes for many applications
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