Input/Output Devices
Chapter 5b
Input
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Allow input into computer
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Data
Commands
Responses
Programs
Most popular input devices are keyboard and
mouse
Keyboard
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Features
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QWERTY layout
12 function keys
Numeric keypad
Cursor control key
Special function keys
Connectors
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PS/2, USB, IrDA (wireless infrared)
Mouse
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Point-and-draw device
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Used in GUI interfaces
Controls on-screen pointer or cursor
Click, double-click, drag
Mechanical mouse use ball pushed over flat surface
to generate mouse positions
Optical mouse uses low laser (LED) to generate
mouse positions
Other types include trackballs, track points, track
pads, joystick and digital pen
Connectors are PS/2, USB or IrDA
Data Source Automation
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Reduces input errors
Computer generates data entry information at
the source f the data
Scanners used to read the data eliminating
need for key entry
Best known example is UPC or universal
product code
Data Source Automation
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Other types
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MICR,or magnetic ink character recognition =
used by banks to encode bank and account
information on checks
OMR, or optical mark recognition. Best example
is scantron used in tests and surveys
OCR, or optical character recognition. Reads
both printed and written text. Used by mail
services to read addresses and zip codes
Turnaround document are sent to customers and
returned with payments
Other inputs
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Magnetic stripe cards
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Data encoded on magnetic stripes
ATM cards, credit/debit cards, badges
Speech recognition or voice input. Requires
special software and quality microphone
Digital cameras and video recorders allow
input of digital pictures and videos.
Output
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Output information from computer in form we
can read
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Text, graphics, audio, video
Most popular output devices are monitor and
printers
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Monitor = “soft copy”
Printer = “hard copy”
Monitors
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Two basic technologies = CRT and flat panel
CRT = cathode ray tube
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Older technology
 Inexpensive
 Bulky and power hog
 Use same technology as TV picture tubes
Flat panel
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Essential for laptops
Gaining popularity with desktops
Light, portable, power misers
More expensive
Most popular technology is LCD or liquid crystal display
Monitors (contd)
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Require graphics adapter
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Converts digital signals to format compatible with monitor
Cards may be integrated into motherboard or use AGP
expansion slot
Cards have their own VRAM or video RAM and processor
chip
Resolution = picture quality
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Pictures displayed as pixels or dots on screen
Higher number of pixels = better resolution
Lower dot pitch (distance between pixels) = better
resolution
Printers
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Two categories – impact and non-impact
Impact printers
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Older technology
Print head strikes paper
Noisy, lower quality output
Advantage is the ability to print carbon copies
(with appropriate paper!)
Best example is dot-matrix printer
Printers (contd)
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Non-impact
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Print heads do not touch paper
Quiet, higher quality printout
Ink-jet printer
 Sprays ink droplets on paper to form text and graphics
 Energy efficient
 Refill cartridges are expensive
Laser printer or page printer
 Same toner technology as copy machines
 Produce one page at a time
 Faster than ink jet printers but power hogs
Other output devices
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Speakers
Speech synthesis systems = use text-tospeech software to produce speech