Chapter 7
Input/Output Technology
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Systems Architecture
Chapter 7
Chapter Goals
• Describe manual input devices and how they
are implemented.
• Explain the characteristics and
implementation technology of video display
devices.
• Understand printer characteristics and
technology.
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Systems Architecture
Chapter 7
Chapter Goals
• Identify the characteristics of audio I/O
devices, and explain how they operate.
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Systems Architecture
Chapter 7
Chapter Topics
• Describes the concepts, technology and
hardware used in communication between
people and computers.
• Understand the importance of I/O technology.
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Systems Architecture
Chapter 7
Chapter Topics
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Systems Architecture
Chapter 7
Manual Input Devices
• Keyboard Input
• Pointing Devices
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Systems Architecture
Chapter 7
Manual Input Devices
Keyboard Input
• Keyboard devices translate keystrokes
directly into electrical signals.
• A keyboard controller is used to generate bit
stream outputs.
• The controller generates a bit stream output
according to an internal program or lookup
table.
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Systems Architecture
Chapter 7
Manual Input Devices
Keyboard Input
• A keyboard controller generates an output
called a scan code.
• A scan code is a one or two-byte data
element that represents a specific keyboard
element.
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Systems Architecture
Chapter 7
Manual Input Devices
Pointing Devices
•
•
•
•
Mouse
Trackball
Joystick
Digitizer Tablet
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Systems Architecture
Chapter 7
Manual Input Devices
Pointing Devices
Translates the spatial position of a pointer,
stylus, or other selection device into numeric
values within a system of two-dimensional
coordinates.
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Systems Architecture
Chapter 7
Manual Input Devices
Mouse – a pointing device that is moved on a
flat surface such as a table, desk or rubber
pad.
Trackball – a mouse with the roller ball on
the top. The roller ball is moved by the
fingertips, thumb or palm of the hand.
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Systems Architecture
Chapter 7
Manual Input Devices
Joystick – used as an input device with
computer games.
Digitizer Tablet – uses a pen, or stylus, and
a digitizing tablet. The tablet is sensitive to
the placement of the stylus at any point on its
surface.
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
• Matrix-Oriented Image Composition
– Fonts
– Color
– Pixel Content
• Image Storage Requirements
• Image Description Languages
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
Matrix-Oriented Image Composition
• Display surfaces can be divided into rows and
columns similar to a large table or matrix.
• Each cell in the table represents one
component of the image.
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
Matrix-Oriented Image Composition
• One of the cells is a pixel.
• The resolution of the display is the number
of pixels displayed per linear measurement
unit.
• Resolution is stated in dots per inch(dpi).
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
• Font – a collection of characters of similar
style and appearance.
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
Color
• For video displays, color is generated directly
by the display device.
• The video display industry has used red,
green and blue as primary colors.
• A video display that generates color uses
mixtures or these colors.
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
Color
• For print, color is light frequency reflected
from the paper.
• The printing industry generates color using
the inverse of the primary video display
colors. (subtractive color)
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
Pixel Content
• Pixel content must be described numerically.
• A stored set of numeric pixel descriptions is
called a bit map.
• A palette is a table of colors.
• Color can also be produced using dithering.
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
Image Storage Requirements
• Image storage requirements apply to images
stored in primary and secondary storage, and
to buffers used in I/O devices.
• Image storage requirements can be reduced
with image compression techniques.
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
Image Storage Requirements
Compression Techniques:
•
Graphics Interchange Format (GIF)
•
Joint Photographic Experts Group (JPEG)
•
Moving Pictures Experts Group (MPEG)
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
Image Description Languages
• Use a symbolic language to describe
primitive image components.
• Can use a vector list .
• Describe the image components that are
straight-line segments or can be built from
segments.
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Systems Architecture
Chapter 7
Basic Concepts of Print and
Display
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Systems Architecture
Chapter 7
Technology Focus - Postscript
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Systems Architecture
Chapter 7
Technology Focus - Postscript
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Systems Architecture
Chapter 7
Video Display
• Character-Oriented Video Display Terminals
• Graphic Video Display Devices
– CRTs
– Flat Panel Displays
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Systems Architecture
Chapter 7
Video Displays
Character-Oriented Video Display Terminals
• Commonly used during 1970s and 1980s.
• Terminal – consist of an integrated keyboard
and television screen.
• Used today primarily in systems such as retail
checkout counters and factory floor
environments.
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Systems Architecture
Chapter 7
Video Display
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Systems Architecture
Chapter 7
Video Display
Graphic Video Display Devices
• Used for displaying diagrams such as
construction blueprints, wireframe models,
writing diagrams and to produce
mathematical graphs.
• By the mid-1980s monitors were
manufactured.
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Systems Architecture
Chapter 7
Video Display
• Monitors operate as independent devices
under control of a video controller attached to
the system bus.
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Systems Architecture
Chapter 7
Video Display
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Systems Architecture
Chapter 7
Video Display
CRT
• Current monitors are implemented using
cathode ray tubes.
• A CRT is an enclosed tube.
• An electron gun in the rear of the tube
generates a stream of electrons.
• Pixel illumination is controlled by pulsing the
electron beam.
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Systems Architecture
Chapter 7
Video Display
• The number of times per second that the
entire surface is scanned by the electron gun
is called the refresh rate.
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Systems Architecture
Chapter 7
Video Display
Flat Panel Display
• Liquid Crystal Display – is a flat panel matrix that
consists of encapsulated liquid crystals sandwiched
between two polarizing panels.
• Passive Active Matrix Display – shares transistors
among rows and columns of pixels.
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Systems Architecture
Chapter 7
Video Display
• Electroluminescent Displays – similar to
construction of LCDs. Color is generated with
three matrices of different colored phosphors.
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Systems Architecture
Chapter 7
Printers and Plotters
•
•
•
•
Dot Matrix Printers
Ink-Jet Printers
Laser Printers
Plotters
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Systems Architecture
Chapter 7
Printers and Plotters
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Systems Architecture
Chapter 7
Printers and Plotters
Dot Matrix Printers
• Generate images through mechanical contact
with ink and papers.
• Character codes received by the print
generator are transmitted as a series of
control commands to the print head.
• Characters are generated one or two vertical
rows at a time.
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Systems Architecture
Chapter 7
Printers and Plotters
Ink-Jet Printers
• Uses a paper movement mechanism similar
to that of a dot matrix printer.
• The print head of an ink-jet printer consists of
an ink cartridge, a set of ink chambers and a
set of ink nozzles.
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Systems Architecture
Chapter 7
Printers and Plotters
Ink-Jet Printers
• Each ink nozzle can print a single pixel and
nozzles are arranged in short vertical rows
similar to those of a dot matrix printer.
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Systems Architecture
Chapter 7
Printers and Plotters
Laser Printers
• Operates differently from other types of
printers.
• No print head or ink ribbon is used.
• An internal image of the entire page is stored
in an internal buffer as a bit map.
• Once filled, the buffer contents are sent to the
print driver for generation.
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Systems Architecture
Chapter 7
Printers and Buffers
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Systems Architecture
Chapter 7
Printers and Plotters
Plotters
• A printer that generates line drawings on wide
sheets or rolls of paper.
• Paper is mounted within a paper control
mechanism that can move the paper up or
down precisely.
• Can handle paper widths up to 60 inches.
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Systems Architecture
Chapter 7
Optical Input Devices
Optical scanning devices can be
differentiated by the following criteria:
•
•
•
•
Input format requirements
Normal and maximum spatial resolution
Normal and maximum chromatic resolution
Embedded processing capacity
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Systems Architecture
Chapter 7
Optical Input Devices
Mark Sensors and Bar Code Scanners
• Mark Sensors – scans for light or dark marks
at specific locations on a page.
• The mark sensors uses preprinted bars on
the edge of the page to establish reference
points.
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Systems Architecture
Chapter 7
Optical Input Devices
Mark Sensors and Bar Code Scanners
• A scanning laser sweeps a narrow laser
beam back and forth across the bar code.
• Bars must have precise width and spacing, as
well as high contrast for accurate decoding.
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Systems Architecture
Chapter 7
Optical Input Devices
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Systems Architecture
Chapter 7
Optical Input Devices
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Systems Architecture
Chapter 7
Optical Input Devices
• Optical Scanners – generate bit map
representations of printed images.
• A bright light is shone on the page and
reflected light is detected by an array of
photodetectors.
• Spatial resolution is determined by the size
and spacing of the photodetectors.
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Systems Architecture
Chapter 7
Optical Input Devices
Optical character recognition (OCR)
• Combine optical scanning technology with
hardware or software interpretation of bit map
content.
• The bit mapped representation is searched
for patterns corresponding to printed
characters.
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Systems Architecture
Chapter 7
Optical Input Devices
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Systems Architecture
Chapter 7
Audio I/O Devices
Sound generation and recognition can be
used in a number of ways.
– General-purpose sound output, such as warnings,
status indicators, and music
– General-purpose sound input, such as digital
recording
– Voice command input
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Systems Architecture
Chapter 7
Audio I/O Devices
Sound generation and recognition can be
used in a number of ways.
– Speech Recognition
– Speech Generation
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Systems Architecture
Chapter 7
Audio I/O Devices
Speech recognition
• The process of recognizing and appropriately
responding to the meaning embedded within
human speech.
• Human speech consists of individual sounds
called phonemes.
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Systems Architecture
Chapter 7
Audio I/O Devices
A number of factors complicate the
process of speech recognition:
– Speaker variability
– Phoneme transitions and combinations
– Real-time processing
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Systems Architecture
Chapter 7
Audio I/O Devices
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Systems Architecture
Chapter 7
Audio I/O Devices
Speech Generation
• A device that generates spoken messages
based on textual input is called audio
response unit.
• Simple audio response units digitally store
and play back words or word sequences.
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Systems Architecture
Chapter 7
Audio I/O Devices
Speech Synthesis
• Individual vocal sounds, or phonemes, are
stored within the system.
• Character outputs are sent to a processor
within the output unit, which assembles
corresponding groups of phonemes to
generate synthetic speech.
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Systems Architecture
Chapter 7
General-Purpose Audio
Hardware
Common names for general-purpose audio
hardware are:
– sound card
– sound board
– multimedia controller
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Systems Architecture
Chapter 7
General-Purpose Audio
Hardware
Sound cards include:
–
–
–
–
–
an analog-to-digital converter (ADC)
a digital-to-analog converter
a low power amplifier
connector for the microphone
a speaker or headphones
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Systems Architecture
Chapter 7
General-Purpose Audio
Hardware
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Systems Architecture
Chapter 7
General-Purpose Audio
Hardware
Musical Instrument Digital Interface (MIDI) –
is a standard for storage and transport of
control information among computers and
electronic instruments.
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Systems Architecture
Chapter 7
Summary
• Manual input devices include keyboards,
mice and other pointing devices.
• Display surfaces can be divided input rows
and columns similar to a large table or matrix.
• A stored set of numeric pixel descriptions is
called a bit map.
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Systems Architecture
Chapter 7
Summary
• Video display terminals consist of an
integrated keyboard and television screen.
• Commonly used paper output devices include
dot matrix printer, ink-jet printer, laser
printers, and plotters.
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Systems Architecture
Chapter 7
Summary
• Optical input devices include optical scanners, mark
sensors, bar code readers, and optical character
recognition devices.
• General-purpose speech recognition systems can be
used for command and control, or for the input of
large amounts of textual material.
• Sound cards include converters, amplifiers,
microphone, speaker and headphone connectors
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