Computer Peripherals – Part II
Computer Peripherals – Part II
Displays
Dika Jatnika
Computer HardWare
Types of Displays
• Two main types
– CRT (cathode ray tubes)
– LCD (liquid crystal display)
• Related terms
– Monitor or screen
• A display is often called a “monitor” or “screen”
• However, the term “monitor” usually refers to the
entire box, where as “screen” often implies just a
Rev: Sec 9.5 pg 262 ff
sub-assembly within the box
Dika Jatnika
Computer HardWare
Layout for a display
Dika Jatnika
Computer HardWare
Pixels
• A Pixel is a “picture element”
– a single point in a graphic image
– A graphics display is divided into thousands (or
millions) of pixels arranged in rows and columns
– The pixels are so close together, they appear connected
– The number of bits used to represent each pixel
determines how many colours or shades of grey can be
represented
– For a B&W (black and white) monitor, each pixel is
represented by 1 bit
– With 8 bits per pixel, a monitor can display 256 shades
or grey or 256 colours (Note: 28 = 256)
Dika Jatnika
Computer HardWare
Display screen ratios
Dika Jatnika
Computer HardWare
Display Size
• Usually specified in “inches”
• Value cited is the diagonal dimension of the
raster -- the viewable area of the display
• E.g., a 15” monitor:
15”
Dika Jatnika
Computer HardWare
Resolution
• Resolution is the number of pixels on a
screen display
• Usually cited as n by m
– n is the number of pixels across the screen
– m is the number of pixels down the screen
• Typical resolutions range from…
– 640 by 480 (low end), to
– 1,600 by 1,200 (high end)
Dika Jatnika
Computer HardWare
Video RAM Requirements
• Total number of pixels is n m
• Examples
– 640 480 = 307,200 pixels
– 1,600 1,200 = 1,920,000 pixels
• Video RAM required equals total number of
pixels times the number of bits/pixel
• Examples
– 640 480 8 = 2,457,600 bits = 307,200 bytes = 300
Kbytes
– 1,600 1,200 24 = 46,080,000 bits = 5,760,000 bytes
= 5,625 Kbytes = 5.49 Mbytes
Dika Jatnika
Computer HardWare
Video RAM (KB) Per Image
Bits per pixel
Resolution
8 bit
16 bit
24 bit
640 x 480
300
600
900
800 x 600
468.75
937.5
1406.25
1024 x 768
768
1536
2304
1152 x 1024
1152
2304
3456
1280 x 1024
1280
2560
3840
1600 x 1200
1875
3750
5625
See previous slide for calculations
Dika Jatnika
Computer HardWare
Aspect Ratio
• Aspect ratio is the ratio of the width to height of a
display screen
• For a 640 by 480 display, the aspect ratio is
640:480, or 4:3
• Related terms
– Landscape
• The width is greater than the height
– Portrait
• The height is greater than the width
Dika Jatnika
Computer HardWare
Color Displays
• CRT displays
– each pixel is composed of three superimposed dots: red,
green, and blue
– Hence, RGB display
– The three dots are created by three separate beams
– Ideally, the three dots should converge at the same
point, however, in practice there is a small amount of
convergence error, and this makes the pixels appear
fuzzy
• LCDs
– Colour is created by filtering/blocking different
frequencies of light
Dika Jatnika
Computer HardWare
CRT Display
Rev: Fig 9.21 pg 267 ff
Dika Jatnika
Computer HardWare
Operation of a CRT Display
• A CRT display contains a vacuum tube
• At one end are three electron guns, one each for
red, green, and blue
• At the other end is a screen with a phosphorous
coating
• The three electron guns fire electrons at the screen
and excite a layer of phosphor
• Depending on the beam, the phosphor glows,
either red, green, or blue
Dika Jatnika
Computer HardWare
Operation of an LCD
• Two sheets of polarizing material with a
liquid crystal solution between them
• An electric current passed through the
liquid causes the crystals to align so that
light cannot pass through them
• Each crystal, therefore, acts like a shutter,
either allowing light to pass through or
blocking the light
Rev: pg 268
Dika Jatnika
Computer HardWare
Dot Pitch
• Dot pitch is a measure of the diagonal distance
between phosphor dots (pixels) on a display
screen
• One of the principal characteristics that determines
the quality of a display
• The lower the number, the crisper the image
• Cited in mm (millimeters)
• Typical values range from 0.15 mm to 0.30 mm
• Note
– Dot pitch, as specified, is the capability of the display
– For a particular image, dot pitch can be calculated as…
Dika Jatnika
Computer HardWare
Dot Pitch Image Example
• Q: What is the dot pitch of an image
displayed on a 15” monitor with a
resolution of 640 by 480?
• A:
Dot pitch = 15 / 800 inches
= 0.01875 inches
= 0.01875 / 0.039 mm
= 0.481 mm
Notes:
1.
2.
Z = (6402 + 4802)1/2 = 800
1 mm = 0.039 inch
Z
480
640
Dika Jatnika
Computer HardWare
Dot Pitch Illustrated
Pixel
0.481 mm
Dika Jatnika
Computer HardWare
Dot Pitch Image Table
Display Size
Resolution
14”
15”
17”
19”
21”
640 x 480
0.45
0.48
0.54
0.61
0.67
800 x 600
0.36
0.38
0.44
0.49
0.54
1024 x 768
0.28
0.30
0.34
0.38
0.42
1152 x 1024
0.23
0.25
0.28
0.32
0.35
1280 x 1024
0.22
0.23
0.27
0.30
0.33
1600 x 1200
0.18
0.19
0.22
0.24
0.27
Note: Dot pitch figures in mm (millimeters)
Dika Jatnika
Computer HardWare
Figure 9.19 Diagram of raster scan generation process
Dika Jatnika
Computer HardWare
Figure 9.17 Use of a color transformation table
Dika Jatnika
Computer HardWare
Dika Jatnika
Computer HardWare
Retracing
• Retracing is the act of repositioning the
electron beam
• The beam must undergo horizontal retrace
(once per line) and vertical retrace (once per
image)
Vertical
retrace
Dika Jatnika
Horizontal
retrace
Computer HardWare
Interlacing
• Interlacing is an image drawing technique
whereby the electron guns draw only half
the horizontal lines with each pass
• The odd lines are drawn on the 1st pass, the
even lines are drawn on the 2nd pass
• A non-interlaced imaged is completely
drawn in one pass
• Let’s see…
Dika Jatnika
Computer HardWare
Interlacing Animation
Non-interlaced scanning
Interlaced scanning
Electron beam “on” (drawing)
Electron beam “off” (retracing)
Dika Jatnika
Computer HardWare
Uses of Interlacing
• TVs use interlaced scanning
• Computer monitors (CRTs) use noninterlaced scanning
Dika Jatnika
Computer HardWare
•
•
Less Demanding on the Monitor More Demanding on the Monitor
•Flickering can be annoying
• No Flickering
Figure 9.18 Interlaced versus noninterlaced raster scan
Dika Jatnika
Computer HardWare
Scan Frequency
• Horizontal scan frequency
– The frequency with which an electron beam moves
back-and-forth
– The rate of drawing each line in an image
– Typical range: 30-65 kHz
• Vertical scan frequency
– The frequency with which an electron beam moves upand-down
– Also called vertical refresh rate , refresh rate, vertical
frequency, vertical scan rate, or frame rate
– The rate of drawing images
– Typical range: 45-120 Hz
Dika Jatnika
Computer HardWare
Video Frequency
• The frequency at which pixels are drawn on
the display
• Specified as a maximum capability of the
monitor
• Also called video bandwidth
• Typical ranges 50-100 MHz
Dika Jatnika
Computer HardWare
Display Properties in Windows
• Right click on the desktop (display) and
select Properties
• Click Settings to determine/change the
setting for Colors and Screen area
(Resolution)
• To determine/change screen refresh rate,
click on Advanced, then click on Adapter
Next 2 slides
Dika Jatnika
Computer HardWare
Note:
Varies on
different
systems
Dika Jatnika
Computer HardWare
Note:
Varies on
different
systems
Dika Jatnika
Demo
Computer HardWare
Video Interfaces (1 of 2)
• Composite video
– Definition: a video interface in which all the colour and
sync information is contained in one signal
– Contrast with RGB
– TVs in North America use composite video
• RGB (Red, Green, Blue)
– Definition: a video interface in which the red, green,
and blue signals, and the horizontal and vertical sync
signals, are separate
– Computer monitors use RGB
Dika Jatnika
Computer HardWare
Video Interfaces (2 of 2)
• S-video
– A technology for transmitting video signals over a
cable by dividing the video information into two
separate signals: one for colour (chrominance, C), and
one for brightness (luminance, Y)
– Also called Y/C video
– Televisions (internally) are designed for separate
luminance and chrominance signals
– Computer monitors are designed for separate red,
green, and blue signals
Dika Jatnika
Computer HardWare
RGB Video Standards
• A variety of standards exist for delivering
RGB signals to a video display monitor
• Developed and consolidated by VESA
(Video Electronics Standards Association)
• Examples
– VGA – video graphics adapter
– SVGA – super-VGA
– XGA – extended graphics adapter
Dika Jatnika
Computer HardWare
VGA/SVGA/XGA Pinouts
Pin
Dika Jatnika
Signal
1
Red
2
Green
3
Blue
4
ID bit 2
5
Ground
6
Red return
7
Green return
8
Blue return
9
-
10
Sync return
11
ID bit 0
12
ID bit 1
13
Horizontal sync
14
Vertical sync
15
-
DE15 connector
Computer HardWare
S-video Pinouts
Pin
Dika Jatnika
Signal
1
Ground
2
Ground
3
Y (luminance)
4
C (Chrominance)
4-pin mini-DIN connector
Computer HardWare
Flat Panel Displays
• A very thin display screen
• Most flat panel displays use LCD
technology
• Other technologies
– ELD (electro-luminescent display)
– Gas plasma display
Dika Jatnika
Computer HardWare
Computer Peripherals – Part III
Chapter 9.6, ff
Dika Jatnika
Computer HardWare
Plan
•
•
•
•
Printers
Scanners
Keyboards
Pointing Devices
Dika Jatnika
Computer HardWare
Printers
• Main types:
– Impact
– Laser
– Ink jet
Impact
Dika Jatnika
Computer HardWare
Impact vs. Non-Impact
• Impact printers physically transfer a dot or
shape to the paper
• Include dot-matrix, belt, & solid line printers
• Non-impact printers spray or lay down the
image
• Impact printers remain important because
they can print multi-part forms (eg: carbon or
NCR copies)
Dika Jatnika
Computer HardWare
Printers
• Main types:
– Dot matrix (sample impact)
– Laser
– Ink jet
Dika Jatnika
Computer HardWare
How it works
( Impact Type Dot-Matrix )
A print-head moves back-and-forth in front of forms
(paper) on which characters or graphic images are transferred.
The print-head contains numerous wires, typically from 9 to
24. Each wire is part of a solenoid-like unit. An electrical
pulse applied to the solenoid creates a magnetic field which
forces the wire to move briefly forward then backward. As
the wire moves forward, it strikes a print ribbon containing
ink. The impact transfers an ink dot to the paper. The paper
is supported from behind by a platen. (a hard flat piece)
Dika Jatnika
Computer HardWare
Illustration
Dika Jatnika
Computer HardWare
Dot Matrix Print Head
One print wire
Print wires
(e.g., 12)
Front view
Dika Jatnika
Side view
Computer HardWare
Dot Matrix Impact Printing
Paper
Print
wire
Platen
Ribbon
Paper
Side view
Dika Jatnika
Side view
Front view
Computer HardWare
Specifications
• cps
– characters per second
– Varies by quality of print (e.g., draft vs. final (NLQ))
• lpm
– lines per minute (related to cps)
• Forms
– Maximum number of layers of paper that can by
printed simultaneously
– Specified as n-part forms (e.g., 4-part forms)
• mtbf
– Mean time between failure (e.g., 6000 hours)
Dika Jatnika
Computer HardWare
Dot Matrix Printer Example
Specifications
• Printhead wires: 9
• Printhead life: 200 million characters
• Print speed:
• near letter quality: 105 cps
• utility: 420 cps
• high speed draft: 550 cps
• Number of copies: 8
• MTBF: 8000 hours
Pacemaker 3410 by OKI Data, Inc.
http://www.okidata.com
Dika Jatnika
Computer HardWare
Printers
• Main types:
– Dot matrix
– Laser
– Ink jet
Dika Jatnika
Computer HardWare
•
Operation of a Laser Printer
Four steps
–
A laser is fired in correspondence to the dots to be printed. A
spinning mirror causes the dots to be fanned out across the drum. The
drum rotates to the next line, usually 1000th or 1600th of an inch.
The drum is photosensitive. As a result of the laser light, the drum
becomes electrically charged wherever a dot is to be printed.
Photosensitive
drum
Laser
Spinning
mirror
Dika Jatnika
Computer HardWare
Top View of Rotating Mirror
Drum
Rotating Mirror:
This one has eight
faces
Laser light source
Dika Jatnika
Computer HardWare
Operation of a Laser Printer
2.
As the drum continues to rotate, the charged part of the drum passes
through a tank of black powder called toner. Toner sticks to the drum
wherever the charge is present. Thus, the pattern of toner on the drum
matches the image.
Toner
Dika Jatnika
Computer HardWare
Operation of a Laser Printer
3.
A sheet of paper is fed toward the drum. A charge wire coats the
paper with electrical charges. When the paper contacts the drum, it
picks up the toner from the drum
Charge
wire
Paper
Dika Jatnika
Computer HardWare
Operation of a Laser Printer
4.
As the paper rolls from the drum, it passes over a heat and pressure
area known as the fusing system. The fusing system melts the toner to
the paper. The printed page then exits the printer.
As the same time, the surface of the drum passes over another wire,
called a corona wire. This wire resets the charge on the drum, to
ready it for the next page.
Corona
wire
Dika Jatnika
Fusing
system
Computer HardWare
Specifications
• ppm
– Pages per minute
– Typically 4-10 ppm
• dpi
– Dots per inch
– Typically 600-1200 dpi
Dika Jatnika
Computer HardWare
Laser Printer Example
Laserjet 5000 Series from Hewlett Packard Co.
(http://www.hp.com)
Dika Jatnika
Computer HardWare
Printers
• Main types:
– Dot matrix
– Laser
– Ink jet
Dika Jatnika
Computer HardWare
Background
• Inkjet technology was developed in the
1960s
• First commercialized by IBM in 1976 with
the 6640 printer
• Cannon and Hewlett Packard developed
similar technology
• Also called bubble jet
Dika Jatnika
Computer HardWare
How it works
Characters and graphics are 'painted‘ line by line to from a pattern of dots as a
print head scans horizontally across the paper. An ink-filled print cartridge is
attached to the inkjet's print head. The print head contains 50 or more ink-filled
chambers, each attached to a nozzle. An electrical pulse flows through thin
resistors at the bottom of each chamber. When current flows through a resistor, the
resistor heats a thin layer of ink at the bottom of the chamber to more than 900
degrees Fahrenheit for several millionths of a second . The ink boils and forms a
bubble of vapour. As the vapour bubble expands, it pushes ink through the nozzle
to form a droplet at the tip of the nozzle. The droplet sprays onto the paper.
The volume of the ejected ink is about one millionth that of a drop of water
from an eye-dropper. A typical character is formed by an array of these drops 20
across and 20 high. As the resistor cools, the bubble collapses. The resulting
suction pulls fresh ink from the attached reservoir into the firing chamber.
Dika Jatnika
Computer HardWare
Inkjet Printer Example
Dika Jatnika
Computer HardWare
Plan
•
•
•
•
Printers
Scanners
Keyboards
Pointing Devices
Dika Jatnika
Computer HardWare
How it works
A scanner works by digitizing an image. A scanning mechanism
consists of a light source and a row of light sensors. As light is reflected
from individual points on the page, it is received by the light sensors and
translated to digital signals that correspond to the brightness of each point.
Colour filters can be used to produce colour images, either by providing
multiple sensors or by scanning the image three times with a separate
colour filter for each pass. The resolution of scanners is similar to that of
printers, approximately 300-600 dpi (dots per inch).
Dika Jatnika
Computer HardWare
Scanners
• Three main types
– Flatbed
– Sheet-fed
– Handheld
Dika Jatnika
Computer HardWare
Flatbed Scanner Example
Dika Jatnika
Computer HardWare
Sheet-fed Scanner Example
OfficeJet Series 700 from Hewlett Packard Co
(http://www.hp.com)
Dika Jatnika
Computer HardWare
Handheld Scanner Example
QuickScan GP Bar Code Scanner from PSC, Inc.
(http://www.pscnet.com)
Dika Jatnika
Computer HardWare
Plan
•
•
•
•
Printers
Scanners
Keyboards
Pointing Devices
Dika Jatnika
Computer HardWare
Examples
Natural keyboard by Microsoft
Dika Jatnika
Internet keyboard by Microsoft
Computer HardWare
Keyboard Connectors
Dika Jatnika
Computer HardWare
Plan
•
•
•
•
Printers
Scanners
Keyboards
Pointing Devices
Dika Jatnika
Computer HardWare
Examples
Dika Jatnika
Computer HardWare
Displays
Dika Jatnika
Computer HardWare
Types of Displays
• Two main types
– CRT (cathode ray tubes)
– LCD (liquid crystal display)
• Related terms
– Monitor or screen
• A display is often called a “monitor” or “screen”
• However, the term “monitor” usually refers to the
entire box, where as “screen” often implies just a
Rev: Sec 9.5 pg 262 ff
sub-assembly within the box
Dika Jatnika
Computer HardWare
Layout for a display
Dika Jatnika
Computer HardWare
Pixels
• A Pixel is a “picture element”
– a single point in a graphic image
– A graphics display is divided into thousands (or
millions) of pixels arranged in rows and columns
– The pixels are so close together, they appear connected
– The number of bits used to represent each pixel
determines how many colours or shades of grey can be
represented
– For a B&W (black and white) monitor, each pixel is
represented by 1 bit
– With 8 bits per pixel, a monitor can display 256 shades
or grey or 256 colours (Note: 28 = 256)
Dika Jatnika
Computer HardWare
Display screen ratios
Dika Jatnika
Computer HardWare
Display Size
• Usually specified in “inches”
• Value cited is the diagonal dimension of the
raster -- the viewable area of the display
• E.g., a 15” monitor:
15”
Dika Jatnika
Computer HardWare
Resolution
• Resolution is the number of pixels on a
screen display
• Usually cited as n by m
– n is the number of pixels across the screen
– m is the number of pixels down the screen
• Typical resolutions range from…
– 640 by 480 (low end), to
– 1,600 by 1,200 (high end)
Dika Jatnika
Computer HardWare
Video RAM Requirements
• Total number of pixels is n m
• Examples
– 640 480 = 307,200 pixels
– 1,600 1,200 = 1,920,000 pixels
• Video RAM required equals total number of
pixels times the number of bits/pixel
• Examples
– 640 480 8 = 2,457,600 bits = 307,200 bytes = 300
Kbytes
– 1,600 1,200 24 = 46,080,000 bits = 5,760,000 bytes
= 5,625 Kbytes = 5.49 Mbytes
Dika Jatnika
Computer HardWare
Video RAM (KB) Per Image
Bits per pixel
Resolution
8 bit
16 bit
24 bit
640 x 480
300
600
900
800 x 600
468.75
937.5
1406.25
1024 x 768
768
1536
2304
1152 x 1024
1152
2304
3456
1280 x 1024
1280
2560
3840
1600 x 1200
1875
3750
5625
See previous slide for calculations
Dika Jatnika
Computer HardWare
Aspect Ratio
• Aspect ratio is the ratio of the width to height of a
display screen
• For a 640 by 480 display, the aspect ratio is
640:480, or 4:3
• Related terms
– Landscape
• The width is greater than the height
– Portrait
• The height is greater than the width
Dika Jatnika
Computer HardWare
Color Displays
• CRT displays
– each pixel is composed of three superimposed dots: red,
green, and blue
– Hence, RGB display
– The three dots are created by three separate beams
– Ideally, the three dots should converge at the same
point, however, in practice there is a small amount of
convergence error, and this makes the pixels appear
fuzzy
• LCDs
– Colour is created by filtering/blocking different
frequencies of light
Dika Jatnika
Computer HardWare
CRT Display
Rev: Fig 9.21 pg 267 ff
Dika Jatnika
Computer HardWare
Operation of a CRT Display
• A CRT display contains a vacuum tube
• At one end are three electron guns, one each for
red, green, and blue
• At the other end is a screen with a phosphorous
coating
• The three electron guns fire electrons at the screen
and excite a layer of phosphor
• Depending on the beam, the phosphor glows,
either red, green, or blue
Dika Jatnika
Computer HardWare
Operation of an LCD
• Two sheets of polarizing material with a
liquid crystal solution between them
• An electric current passed through the
liquid causes the crystals to align so that
light cannot pass through them
• Each crystal, therefore, acts like a shutter,
either allowing light to pass through or
blocking the light
Rev: pg 268
Dika Jatnika
Computer HardWare
Dot Pitch
• Dot pitch is a measure of the diagonal distance
between phosphor dots (pixels) on a display
screen
• One of the principal characteristics that determines
the quality of a display
• The lower the number, the crisper the image
• Cited in mm (millimeters)
• Typical values range from 0.15 mm to 0.30 mm
• Note
– Dot pitch, as specified, is the capability of the display
– For a particular image, dot pitch can be calculated as…
Dika Jatnika
Computer HardWare
Dot Pitch Image Example
• Q: What is the dot pitch of an image
displayed on a 15” monitor with a
resolution of 640 by 480?
• A:
Dot pitch = 15 / 800 inches
= 0.01875 inches
= 0.01875 / 0.039 mm
= 0.481 mm
Notes:
1.
2.
Z = (6402 + 4802)1/2 = 800
1 mm = 0.039 inch
Z
480
640
Dika Jatnika
Computer HardWare
Dot Pitch Illustrated
Pixel
0.481 mm
Dika Jatnika
Computer HardWare
Dot Pitch Image Table
Display Size
Resolution
14”
15”
17”
19”
21”
640 x 480
0.45
0.48
0.54
0.61
0.67
800 x 600
0.36
0.38
0.44
0.49
0.54
1024 x 768
0.28
0.30
0.34
0.38
0.42
1152 x 1024
0.23
0.25
0.28
0.32
0.35
1280 x 1024
0.22
0.23
0.27
0.30
0.33
1600 x 1200
0.18
0.19
0.22
0.24
0.27
Note: Dot pitch figures in mm (millimeters)
Dika Jatnika
Computer HardWare
Figure 9.19 Diagram of raster scan generation process
Dika Jatnika
Computer HardWare
Figure 9.17 Use of a color transformation table
Dika Jatnika
Computer HardWare
Dika Jatnika
Computer HardWare
Retracing
• Retracing is the act of repositioning the
electron beam
• The beam must undergo horizontal retrace
(once per line) and vertical retrace (once per
image)
Vertical
retrace
Dika Jatnika
Horizontal
retrace
Computer HardWare
Interlacing
• Interlacing is an image drawing technique
whereby the electron guns draw only half
the horizontal lines with each pass
• The odd lines are drawn on the 1st pass, the
even lines are drawn on the 2nd pass
• A non-interlaced imaged is completely
drawn in one pass
• Let’s see…
Dika Jatnika
Computer HardWare
Interlacing Animation
Non-interlaced scanning
Interlaced scanning
Electron beam “on” (drawing)
Electron beam “off” (retracing)
Dika Jatnika
Computer HardWare
Uses of Interlacing
• TVs use interlaced scanning
• Computer monitors (CRTs) use noninterlaced scanning
Dika Jatnika
Computer HardWare
•
•
Less Demanding on the Monitor More Demanding on the Monitor
•Flickering can be annoying
• No Flickering
Figure 9.18 Interlaced versus noninterlaced raster scan
Dika Jatnika
Computer HardWare
Scan Frequency
• Horizontal scan frequency
– The frequency with which an electron beam moves
back-and-forth
– The rate of drawing each line in an image
– Typical range: 30-65 kHz
• Vertical scan frequency
– The frequency with which an electron beam moves upand-down
– Also called vertical refresh rate , refresh rate, vertical
frequency, vertical scan rate, or frame rate
– The rate of drawing images
– Typical range: 45-120 Hz
Dika Jatnika
Computer HardWare
Video Frequency
• The frequency at which pixels are drawn on
the display
• Specified as a maximum capability of the
monitor
• Also called video bandwidth
• Typical ranges 50-100 MHz
Dika Jatnika
Computer HardWare
Display Properties in Windows
• Right click on the desktop (display) and
select Properties
• Click Settings to determine/change the
setting for Colors and Screen area
(Resolution)
• To determine/change screen refresh rate,
click on Advanced, then click on Adapter
Next 2 slides
Dika Jatnika
Computer HardWare
Note:
Varies on
different
systems
Dika Jatnika
Computer HardWare
Note:
Varies on
different
systems
Dika Jatnika
Demo
Computer HardWare
Video Interfaces (1 of 2)
• Composite video
– Definition: a video interface in which all the colour and
sync information is contained in one signal
– Contrast with RGB
– TVs in North America use composite video
• RGB (Red, Green, Blue)
– Definition: a video interface in which the red, green,
and blue signals, and the horizontal and vertical sync
signals, are separate
– Computer monitors use RGB
Dika Jatnika
Computer HardWare
Video Interfaces (2 of 2)
• S-video
– A technology for transmitting video signals over a
cable by dividing the video information into two
separate signals: one for colour (chrominance, C), and
one for brightness (luminance, Y)
– Also called Y/C video
– Televisions (internally) are designed for separate
luminance and chrominance signals
– Computer monitors are designed for separate red,
green, and blue signals
Dika Jatnika
Computer HardWare
RGB Video Standards
• A variety of standards exist for delivering
RGB signals to a video display monitor
• Developed and consolidated by VESA
(Video Electronics Standards Association)
• Examples
– VGA – video graphics adapter
– SVGA – super-VGA
– XGA – extended graphics adapter
Dika Jatnika
Computer HardWare
VGA/SVGA/XGA Pinouts
Pin
Dika Jatnika
Signal
1
Red
2
Green
3
Blue
4
ID bit 2
5
Ground
6
Red return
7
Green return
8
Blue return
9
-
10
Sync return
11
ID bit 0
12
ID bit 1
13
Horizontal sync
14
Vertical sync
15
-
DE15 connector
Computer HardWare
S-video Pinouts
Pin
Dika Jatnika
Signal
1
Ground
2
Ground
3
Y (luminance)
4
C (Chrominance)
4-pin mini-DIN connector
Computer HardWare
Flat Panel Displays
• A very thin display screen
• Most flat panel displays use LCD
technology
• Other technologies
– ELD (electro-luminescent display)
– Gas plasma display
Dika Jatnika
Computer HardWare
Computer Peripherals – Part III
Chapter 9.6, ff
Dika Jatnika
Computer HardWare
Plan
•
•
•
•
Printers
Scanners
Keyboards
Pointing Devices
Dika Jatnika
Computer HardWare
Printers
• Main types:
– Impact
– Laser
– Ink jet
Impact
Dika Jatnika
Computer HardWare
Impact vs. Non-Impact
• Impact printers physically transfer a dot or
shape to the paper
• Include dot-matrix, belt, & solid line printers
• Non-impact printers spray or lay down the
image
• Impact printers remain important because
they can print multi-part forms (eg: carbon or
NCR copies)
Dika Jatnika
Computer HardWare
Printers
• Main types:
– Dot matrix (sample impact)
– Laser
– Ink jet
Dika Jatnika
Computer HardWare
How it works
( Impact Type Dot-Matrix )
A print-head moves back-and-forth in front of forms
(paper) on which characters or graphic images are transferred.
The print-head contains numerous wires, typically from 9 to
24. Each wire is part of a solenoid-like unit. An electrical
pulse applied to the solenoid creates a magnetic field which
forces the wire to move briefly forward then backward. As
the wire moves forward, it strikes a print ribbon containing
ink. The impact transfers an ink dot to the paper. The paper
is supported from behind by a platen. (a hard flat piece)
Dika Jatnika
Computer HardWare
Illustration
Dika Jatnika
Computer HardWare
Dot Matrix Print Head
One print wire
Print wires
(e.g., 12)
Front view
Dika Jatnika
Side view
Computer HardWare
Dot Matrix Impact Printing
Paper
wire
Platen
Ribbon
Paper
Side view
Dika Jatnika
Side view
Front view
Computer HardWare
Specifications
• cps
– characters per second
– Varies by quality of print (e.g., draft vs. final (NLQ))
• lpm
– lines per minute (related to cps)
• Forms
– Maximum number of layers of paper that can by
printed simultaneously
– Specified as n-part forms (e.g., 4-part forms)
• mtbf
– Mean time between failure (e.g., 6000 hours)
Dika Jatnika
Computer HardWare
Dot Matrix Printer Example
Specifications
• Printhead wires: 9
• Printhead life: 200 million characters
• Print speed:
• near letter quality: 105 cps
• utility: 420 cps
• high speed draft: 550 cps
• Number of copies: 8
• MTBF: 8000 hours
Pacemaker 3410 by OKI Data, Inc.
http://www.okidata.com
Dika Jatnika
Computer HardWare
Printers
• Main types:
– Dot matrix
– Laser
– Ink jet
Dika Jatnika
Computer HardWare
•
Operation of a Laser Printer
Four steps
–
A laser is fired in correspondence to the dots to be printed. A
spinning mirror causes the dots to be fanned out across the drum. The
drum rotates to the next line, usually 1000th or 1600th of an inch.
The drum is photosensitive. As a result of the laser light, the drum
becomes electrically charged wherever a dot is to be printed.
Photosensitive
drum
Laser
Spinning
mirror
Dika Jatnika
Computer HardWare
Top View of Rotating Mirror
Drum
Rotating Mirror:
This one has eight
faces
Laser light source
Dika Jatnika
Computer HardWare
Operation of a Laser Printer
2.
As the drum continues to rotate, the charged part of the drum passes
through a tank of black powder called toner. Toner sticks to the drum
wherever the charge is present. Thus, the pattern of toner on the drum
matches the image.
Toner
Dika Jatnika
Computer HardWare
Operation of a Laser Printer
3.
A sheet of paper is fed toward the drum. A charge wire coats the
paper with electrical charges. When the paper contacts the drum, it
picks up the toner from the drum
Charge
wire
Paper
Dika Jatnika
Computer HardWare
Operation of a Laser Printer
4.
As the paper rolls from the drum, it passes over a heat and pressure
area known as the fusing system. The fusing system melts the toner to
the paper. The printed page then exits the printer.
As the same time, the surface of the drum passes over another wire,
called a corona wire. This wire resets the charge on the drum, to
ready it for the next page.
Corona
wire
Dika Jatnika
Fusing
system
Computer HardWare
Specifications
• ppm
– Pages per minute
– Typically 4-10 ppm
• dpi
– Dots per inch
– Typically 600-1200 dpi
Dika Jatnika
Computer HardWare
Laser Printer Example
Laserjet 5000 Series from Hewlett Packard Co.
(http://www.hp.com)
Dika Jatnika
Computer HardWare
Printers
• Main types:
– Dot matrix
– Laser
– Ink jet
Dika Jatnika
Computer HardWare
Background
• Inkjet technology was developed in the
1960s
• First commercialized by IBM in 1976 with
the 6640 printer
• Cannon and Hewlett Packard developed
similar technology
• Also called bubble jet
Dika Jatnika
Computer HardWare
How it works
Characters and graphics are 'painted‘ line by line to from a pattern of dots as a
print head scans horizontally across the paper. An ink-filled print cartridge is
attached to the inkjet's print head. The print head contains 50 or more ink-filled
chambers, each attached to a nozzle. An electrical pulse flows through thin
resistors at the bottom of each chamber. When current flows through a resistor, the
resistor heats a thin layer of ink at the bottom of the chamber to more than 900
degrees Fahrenheit for several millionths of a second . The ink boils and forms a
bubble of vapour. As the vapour bubble expands, it pushes ink through the nozzle
to form a droplet at the tip of the nozzle. The droplet sprays onto the paper.
The volume of the ejected ink is about one millionth that of a drop of water
from an eye-dropper. A typical character is formed by an array of these drops 20
across and 20 high. As the resistor cools, the bubble collapses. The resulting
suction pulls fresh ink from the attached reservoir into the firing chamber.
Dika Jatnika
Computer HardWare
Inkjet Printer Example
Dika Jatnika
Computer HardWare
Plan
•
•
•
•
Printers
Scanners
Keyboards
Pointing Devices
Dika Jatnika
Computer HardWare
How it works
A scanner works by digitizing an image. A scanning mechanism
consists of a light source and a row of light sensors. As light is reflected
from individual points on the page, it is received by the light sensors and
translated to digital signals that correspond to the brightness of each point.
Colour filters can be used to produce colour images, either by providing
multiple sensors or by scanning the image three times with a separate
colour filter for each pass. The resolution of scanners is similar to that of
printers, approximately 300-600 dpi (dots per inch).
Dika Jatnika
Computer HardWare
Scanners
• Three main types
– Flatbed
– Sheet-fed
– Handheld
Dika Jatnika
Computer HardWare
Flatbed Scanner Example
Dika Jatnika
Computer HardWare
Sheet-fed Scanner Example
OfficeJet Series 700 from Hewlett Packard Co
(http://www.hp.com)
Dika Jatnika
Computer HardWare
Handheld Scanner Example
QuickScan GP Bar Code Scanner from PSC, Inc.
(http://www.pscnet.com)
Dika Jatnika
Computer HardWare
Plan
•
•
•
•
Printers
Scanners
Keyboards
Pointing Devices
Dika Jatnika
Computer HardWare
Examples
Natural keyboard by Microsoft
Dika Jatnika
Internet keyboard by Microsoft
Computer HardWare
Keyboard Connectors
Dika Jatnika
Computer HardWare
Plan
•
•
•
•
Printers
Scanners
Keyboards
Pointing Devices
Dika Jatnika
Computer HardWare
Examples
Dika Jatnika
Computer HardWare