ITEC 1000 “Introduction to Information Technology”
Lecture 10
Computer Peripherals
1
Lecture Template:
Peripherals
 Storage Devices
 Displays
 Printers
 Scanners
 Pointing Devices

2
Peripherals

Devices that are external to the main
processing function of the computer
Not the CPU, memory, power supply


Classified as input, output, and storage
Connected via
Ports
• parallel, USB, serial
Interface to systems bus
• SCSI, IDE, PCMCIA
3
Storage Devices: Terminology

Medium
• The technology or product type that holds the
data

Access time
• The time to locate data and read it
• Specified as an average in seconds (e.g., s, ms,
µs, ns, etc.)

Throughput/Transfer rate
• Amount of data (in consecutive bytes) moved
per second
• Specified in bytes/s (e.g., Kbytes/s, Mbytes/s)
4
Storage Devices



Primary memory (cache, conventional
memory) – immediate access by CPU
Expanded storage (e.g., RAM) – a buffer
between conventional memory and
secondary memory)
Secondary storage
Data and programs must be copied to primary
memory for CPU access
Permanence of data
Mechanical devices
Direct access storage devices (DASDs)
Online storage
Offline storage – loaded when needed
5
Storage Hierarchy
Primary
storage
Secondary
storage
Offline
storage
Medium
CPU registers
Cache memory
Conventional memory
Expanded memory
Hard disk
Floppy disk
CD-ROM
Tape
Access Time
15-30 ns
50-100 ns
75-500 ns
10-50 ms
95 ms
100-600 ms
0.5+ s
Throughput
600-6000 Kbytes/s
100-200 Kbytes/s
150-1000 Kbytes/s
5-20 Kbytes/s (cartridge)
200-3000 Kbytes/s (reel-to-reel)
6
Storage Devices: Terminology

Online storage
Memory that is accessible to programs without
human intervention
Primary storage and secondary storage are
“online”

Primary storage
Semiconductor technology (e.g., RAM)
Volatile (contents might be lost when powered
off )

Secondary storage
Magnetic technology (e.g., disk drives)
Non-volatile (contents are retained in the
absence of power)
7
Storage Devices: Terminology

Offline storage
Memory that requires human intervention in
order for it to be accessed by a program (e.g.,
loading a tape)
Sometimes called “archival storage”

Direct Access Storage Device (DASD)
Pronounced “dazz-dee”
Term coined by IBM
Distinguishes disks (disk head moves “directly”
to the data) from tapes (tape reel must wind
forward or backward to the data: sequential
access)
8
Secondary Storage Devices
Hard drives, floppy drives
 CD-ROM and DVD-ROM drives
 CD-R, CD-RW, DVD-RAM, DVD-RW
 Tape drives
 Network drives
 Direct access vs. Sequential access
 Rotation vs. Linear

9
Magnetic Disks




A magnetic substance is coated on a round surface
The magnetic substance can be polarized in one of
two directions with an electromagnet (“writing
data”)
The electromagnet can also sense the direction of
magnetic polarization (“reading data”)
Similar to a read/write head on a tape recorder
(except the information is digital rather than
analogue)
10
Magnetic Disks

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Track – circle
Cylinder – same track on all platters
Block – small arc of a track
Sector – pie-shaped part of a platter
Head – reads data off the disk
Head crash
Parked heads
Number of bits on each track is the same! Denser
towards the center.
CAV – constant angular velocity
Spins the same speed for every track
Hard drives – 3600 rpm – 7200 rpm
Floppy drives – 360 rpm
11
Floppy Disks






Also called “flexible disks” or “diskettes”
The platter is “floppy”, or flexible (e.g.,
mylar) (typical: 5.25”, 3.5”)
Most floppy disk drives can hold one
diskette (two surfaces)
The diskette is removable
Typical rpm: 300, 360
Capacities: 180 KB to 1.4 MB (& up to 100
MB “zip” disks, more)
12
Floppy Disk: Example
Access window
Shutter
Cutaway
showing disk
Case
Spindle
Write
protect tab
13
Hard Disks



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

The platter is “hard” (e.g., aluminum)
Most hard disk drives contain more than
one platter
On most hard disk drives, the disks are
“fixed” (i.e., not removable)
On some hard disk drives, the disks are in
a removable pack (hence, “disk pack”)
Typical speed of rotation: 3600, 5400,
7200 rpm (rpm = “revolutions per
minute”)
Capacities: 5 MB to 1+ TB (terabyte = 240
bytes)
14
Hard Disks: Example
Top view of a 36 GB, 10,000
RPM, IBM SCSI
server hard disk, with its top
cover removed, 10 stacked
platters
(The IBM Ultrastar 36ZX)
15
Winchester Disks

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Invented by IBM
A type of hard disk drive
The disk is contained within a sealed unit
No dust particles
When powered off, the head is “parked” at the
outer edge of the platter and rests on the platter
surface
When powered on, the aerodynamics of the head
and enclosure create a cushion of air between the
head and the disk surface
The head floats above the surface (very close!) and
does not touch the surface
Thus, “head crash” (the head touches the surface,
with damage resulting)
16
Winchester Disks: Example
IBM's
Winchester disk
was a
removable
cartridge, but
the heads and
platters were
built in a sealed
unit and were
not separable
http://encyclopedia2.thefreedictionary.com/
17
Hard Disk Layout
Head
Block
Head
motor
Platter
Sector
Track
Cylinder
Track
Drive
motor
Head
assembly
Head, on
moving arm
18
Hard Disk: Terminology

Platter
• A round surface – the disk – containing a magnetic coating

Track
• A circle on the disk surface on which data are contained

Head
• A transducer attached to an arm for writing/reading data
to/from the disk surface

Head assembly
• A mechanical unit holding the heads and arms
• All the head/arm units move together, via the head
assembly

Cylinder
• A set of tracks simultaneously accessible from the heads
on the head assembly
19
Hard Disk: Terminology

Drive motor
The motor that rotates the platters
Typically a DC motor (DC = direct current)
The disk rotates at a fixed speed (e.g., 3600
rpm, revolutions per minute)

Head motion
A mechanism is required to move the head
assembly in/out
Two possibilities:
A stepper motor (digital, head moves in steps, no
feedback)
A servo motor (analogue, very precision positioning,
but requires feedback)
20
Hard Disk: Terminology

Sector
That portion of a track falling along a predefined pieshaped portion of the disk surface
The number of bytes stored in a sector is the same,
regardless of where the sector is located; thus, the density
of bits is greater for sectors near the centre of the disk
The rotational speed is constant; i.e., constant angular
velocity
Thus, the transfer rate is the same for inner sectors and
outer sectors

Block
The smallest unit of data that can be written or read
to/from the disk (typically 512 bytes)
21
Locating a Block of Data
Seek Time
Latency Time
Latency
Transfer Rate
Transfer
Head
Seek
Desired
track
Note: Access time = seek time + latency
22
Hard Disk: Terminology

Seek time
• The time for the head to move to the correct track
• Specified as an average for all tracks on the disk surface

Latency time
• The time for the correct block to arrive at the head once
the head is positioned at the correct track
• Specified as an average, in other words, ½ the period of
rotation
• Also called “rotational delay”

Access time is the time “to get to” the data
(remember!)
• Access time = seek time + latency

Transfer rate
• Same as throughput
23
Disk Access Times

Avg. Seek time
average time to move from one track to another

Avg. Latency time
average time to rotate to the beginning of the
sector
Avg. Latency time = ½ * 1/rotational speed

Transfer time
1/(# of sectors * rotational speed)

Total Time to access a disk block
Avg. seek time + avg. latency time + avg. transfer time
24
Latency Example
A hard disk rotates at 3600 rpm
 What is the average latency?

Period of rotation = (1 / 3600) minutes
= (1 / 3600)  60 seconds
= 0.01667 s
= 16.67 ms
Average latency
= 16.67 / 2 ms
= 8.33 ms
25
Factors Determining Transfer Rate

Transfer rate can be determined,
given…
Rotational speed of the disk platters
Number of sectors per track
Number of bytes per sector
26
Transfer Rate: Example

Q: Determine the transfer rate, in
Mbytes/s, for a hard disk drive, given
Rotational speed = 7200 rpm
Sectors per track = 30
Data per sector = 512 bytes = 0.5 Kbytes

A:
Transfer rate =
sectors/min
=
Kbytes/min
=
=
7200 x 30 = 216,000
216,000 x 0.5 = 108,000
108,000 / 60 = 1,800 Kbytes/s
1,800 / 210 = 1.76 Mbytes/s
27
Exercise - Transfer Rate

Q: Determine the transfer rate, in
Mbytes/s, for a hard disk drive, given
• Rotational speed = 7000 rpm
• Sectors per track = 32
• Data per sector = 1024 bytes
Skip answer
Answer
28
Exercise - Transfer Rate
Answer

Q: Determine the transfer rate, in
Mbytes/s, for a hard disk drive, given
• Rotational speed = 7000 rpm
• Sectors per track = 32
• Data per sector = 1024 bytes = 1 Kb
A: Transfer rate = 7000 x 32 = 224,000 sectors/min
= 224,000 x 1 = 224,000 Kbytes/min
= 224,000 / 60 = 3,733 Kbytes/s
= 3,733 / 210
= 3.65 Mbytes/s
29
Typical Spec’s
Specification
3 ½” Floppy
2 GB Hard Disk
1/2
5/9
Cylinders
80
4160
Sectors/track
18
Varies
512
512
Capacity
1.44 MB
2.1 GB
Rotation speed
360 rpm
7200 rpm
Avg. seek time
95 ms
8.5 ms
Latency
83 ms
4.2 ms
54 Kbyte/s
10 Mbyte/s
Platters/heads
Block size
Transfer rate
30
Track Format

Format of each track:
Previous sector
gap
header
Sector
data
Next sector
CRC
gap
Inter-block
gap
Inter-block
gap
Note:
CRC stands for “cyclic redundancy check”. It’s the
“footer” at the end of each sector. CRC is a
sophisticated form of parity for checking that the
data read are accurate
31
Disk Block Formats
Single Data Block
Header for Windows
disk
32
Disk Formatting
The track positions, blocks, headers,
and gaps must be established before
a disk can be used
 The process for doing this is called
“formatting”
 The header, at the beginning of each
sector, uniquely identifies the sector,
e.g., by track number and sector
number

33
Disk Controller

Interface between the disk drive and
the system is known as a “disk
controller”
May also require special driver,
as in CD-ROMs


A primary function is to ensure data
read/write operations are from/to the
correct sector
Since data rate to/from the disk is
different than data rate to/from system
memory, “buffering” is needed
34
Buffering
Example: Reading data from a disk
System
Disk
controller
RAM
2. Transfer data from buffer to
system RAM (Note: this is a
DMA operation)
Buffer
(RAM)
Disk
1. Read data from disk into a
buffer in the disk controller
35
Multi-block Transfers (1 of 2)
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The smallest transfer is one block (e.g., 512 bytes)
However, often multi-block transfers are required
The inter-block gap provides “time” for the
controller electronics to adjust from the end of one
sector to the beginning of the next
“time” may be needed for a few reasons:
Compute and/or verify the CRC bytes
Switch circuits from read mode to write mode
During a write operation the header is “read” but the data
are “written”
(Remember, the header is only “written” during formatting.)
Perform a DMA operation
36
Multi-block Transfers (2 of 2)
Sometimes, sectors simply cannot be
read or written consecutively
 There is not enough time (see
preceding slide)
 The result is lost performance
because the disk must undergo a full
revolution to read the next sector
 The solution: interleaving

37
Magnetic Disks

Data Block Format
Interblock gap
Header
Data
Formatting disk
Disk Interleaving
Disk Interleaving
 Disk Arrays

RAID – mirrored, striped
Majority logic  fault-tolerant
computers
38
Interleaving

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Rather than numbering blocks
consecutively, the system skips one or
more blocks in its numbering
This allows multi-block transfers to occur
as fast as possible
Interleaving minimizes lost time due to
latency
Interleaving “factor” (see next slide) is
established when the disk is formatted
Can have a major impact on system
performance
39
Interleaving Examples
Factor
1:1
1
2:1
1
3:1
1
2
3
4
2
5
3
2
6
7
4
3
8
9
etc.
5
etc.
etc.
40
2:1 Interleaving
2
6
1
7
5
3
8
9
4
41
File System Considerations
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
There is no direct relationship between the size
and physical layout of blocks on a disk drive and
the size and organization of files on a system
File system
Determines the organization of information on a
computer
Performs logical-to-physical mapping of information
A file system is part of each and every operating system

Logical mapping
The way information is perceived to be stored

Physical mapping
The way information is actually stored
42
Alternate Disk Technologies

Removable hard drives
Disk pack – disk platters are stored in a plastic
case that is removable
Another version includes the disk head and arm
assembly in the case

Fixed-head disk drives
One head per track
Eliminates the seek time

Bernoulli Disk Drives
Hybrid approach that incorporates both floppy
and hard disk technology
Zip drives
43
Removable hard disks
Also called “disk packs”
 A stack of hard disks enclosed in a metal or
plastic removable cartridge
 Advantages

• High capacity and fast, like hard disk drives
• Portable, like floppy disks

Disadvantage
• Expensive
44
Fixed heads

Fewer tracks but eliminates seek time
Disk
Spindle
Moving head
Fixed heads
45
R.A.I.D. = Redundant array of
inexpensive disks
A category of disk drive that employs two
or more drives in combination for fault
tolerance and performance
 Frequently used on servers, but not
generally used on PCs
 There are a number of different R.A.I.D.
“levels” (next slide)

46
R.A.I.D. Levels (1 of 2)

Level 0
Provides “data striping” (spreading out blocks of
each file across multiple disks)
No redundancy
Improves performance, but does not deliver
“fault tolerance”

Level 1
Provides “data mirroring”: (a.k.a.: “shadowing”)
Data are written to two duplicate disks
simultaneously
If one drive fails, the system can switch to the
other without loss of data or service
Delivers fault tolerance
47
R.A.I.D. Levels (2 of 2)

Level 3
Same as level 0, but also reserves one
dedicated disk for error correction data
Good performance, and some level of
fault tolerance

Level 5
Data striping at the byte level and stripe
error correction information
Excellent performance, good fault
tolerance
48
Fault Tolerance
The ability of a computer system to
respond gracefully to unexpected hardware
or software failure
 Many levels of fault tolerance

• E.g., the ability to continue operating in the
event of a power failure

Some systems “mirror” all operations
• Every operation is performed on two or more
duplicate systems, so if one fails, another can
take over
49
Data Mirroring (Shadowing)
A technique in which data are written to
two duplicate disks simultaneously
 If one disk fails, the system can instantly
switch to the other disk without loss of data
or service
 Used commonly in on-line database
systems where it is critical that data are
accessible at all times

50
Data Striping
A technique for spreading data over
multiple disks
 Speeds operations that retrieve data from
disk storage
 Data are broken into units (blocks) and
these are spread across the available disks
 Implementations allow selection of data
units size, or stripe width

51
Magnetic Tape
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Offline storage
Archival purposes
Disaster recovery (backup)
Tape Cartridges
20 – 144 tracks (side by side)
Read serially (tape backs up)
QIC – quarter inch cartridge (larger size)
DAT – digital audio tape (small size)
Size typically includes (2:1 compression)
52
Types of Tape Drives

Two types:
Reel-to-reel
Used on mainframe computers
Cartridge (including cassette, VHS)
Used on PCs


In either case, the tape can be removed
from the drive (i.e., the tape drive supports
offline storage)
When a tape is loaded in a tape drive and
is ready to be accessed, the tape is
mounted
53
Reel to Reel Tape Drive
54
Tape Reels
55
Tape Reel Specifications

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Reel diameter: 10 ½”
Tape width: ½”
Tape length: 2400 feet
Number of tracks: 9
Drive has nine read/write heads
9 bits of data are read/written at a time (8
data + parity)
Each group of nine bits is called a frame
Data density/capacity
1600 frames/inch  2400 x 12 x 1600 =
46,080,000 bytes/reel
6250 frames/inch  2400 x 12 x 6250 =
1,800,000,000 bytes/reel
56
Nine-track Tape Layout
Physical
record
Inter-record
gap
Track 1
½”
Track 9
1 byte of data
(8 data bits + parity)
57
Tape Cartridge
58
Types of Tape Cartridges
QIC (Quarter Inch Cartridge)
 DAT (Digital Audio Tape)

59
QIC (Quarter Inch Cartridge)
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Pronounced: quick
Introduced in 1970s
Popular format for backing up personal
computers
Two general classes
Full-sized, 5¼” (also called “data cartridge”)
Mini-cartridge, 3½”

Capacities up to 10 GB
60
DAT (Digital Audio Tape)
Tape width: 8 mm or 4 mm
 Uses helical scan technique to record
data (like VCRs)
 Capacities to 24 GB (4 mm) or 40 GB
(8 mm)

61
Optical Storage




Uses light generated by lasers to record and
retrieve information
Information is stored by varying the light
reflectance characteristics of the medium
Reflected light off a mirrored or pitted surface
CD-ROM
Spiral 3 miles long, containing 15 billion bits!
CLV – all blocks are same physical length
Block – 2352 bytes
2k of data (2048 bytes)
16 bytes for header (12 start, 4 id)
288 bytes for advanced error control

DVD-ROM
4.7G per layer
Max 2 layers per side, 2 sides = 17G
62
CD-ROM
CD-ROM stands for “compact disc,
read-only memory”
 Evolved from audio CDs
 Disk size: 120 mm (5¼”)
 Capacity: 550 MB

63
CD-ROMs
General Speed
Seek Time
(milliseconds)
Single-Speed
600
150K per second
2X
320
300K per second
3X
250
450K per second
4X
135-180
600K per second
6X
135-180
900K per second
8X
135-180
1.2 MBps
10X
135-180
1.6 MBps
12X
100-150
1.8 MBps
16X
100-150
2.4 MBps (maximum)
24X
100-150
3.6 Mbps (maximum)
32X
100-150
4.8 Mbps (maximum)
Data Transfer Rate
64
Layout: CD-ROM vs. Standard Disk
CD-ROM
Hard Disk
65
CD-ROM vs. Magnetic Disk


CD-ROM
One spiral track (3
miles long!)
Constant bit density


Magnetic Disk
Multiple tracks of
concentric circles
Variable bit density

Disk speed varies
(CLV, constant linear
velocity)

Disk speed constant
(CAV, constant
angular velocity)

Constant transfer rate

Constant transfer rate

Capacity: 550 MB

Capacity: varies
66
CD-ROM Data Organization


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

270,000 blocks of 2048 bytes each
(typically)
270,000  2048 = 552,960,000 bytes
Extensive error checking and correction
(e.g., bad regions of the disk flagged)
Substantial overhead for error correction
and identifying blocks
Capacity can be as high as 630 MB
67
Optical Storage


Laser strikes land: light reflected into
detector
Laser strikes a pit: light scattered
68
Pits and Lands (1 of 2)





Data are stored as “pits” and “lands”
These are burned into a master disk by a
high powered laser
Master disk is reproduced mechanically by
a stamping process. ( Like a coin, sort of )
Data surface is protected by a clear coating
Data are read by sensing the reflection of
laser light
A pit scatters the light
A land reflects the light
69
Pits and Lands (2 of 2)
Pit
Land
Scattered
light
Laser
Reflected
light
Laser
70
CD-ROM Read Process
Land
Pit
Transparent
protective layer
Prism
Laser
diode
Light
detector
More detail
71
WORM Disks and Drives







WORM = Write-once, read many
Also called CD-R, for CD Recordable
Begin with blank CDs
WORMs drives are used to write the CD
The write process is irreversible
Many standards, some disks may be read
on standard CD-ROM drive, others may not
Applications
Infrequent data distribution
Small quantities
For large quantities, cheaper to have CD-ROMs
manufactured
72
Magneto Optical





Disk may be written, read, and rewritten
Write process is preformed at high
temperature
Combines features of optical and magnetic
technology
Data are stored as a magnetic charge on
the disk surface
During reading, the polarity of the reflected
light is sensed (not the intensity)
73
Displays



Pixel – picture element
Size: diagonal length of screen
Resolution (pixels on screen)
VGA: 480 x 640
SVGA: 600 x 800
768 x 1024
1280 x 1024

Picture size calculation
Resolution * bits required to represent number of
colors in picture
Example: 16 color image, 100 pixels by 50 pixels
4 bits (16 colors) * 100 * 50 = 20,000 bits
74
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)75
Display Size



Usually specified in “inches” and measured
diagonally
Value cited is the diagonal dimension of the
raster -- the viewable area of the display
E.g., a 15” monitor: ( v.i.s. = ?? 13.6? )
15”
76
Display 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)
77
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
78
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
79
Aspect Ratio



Aspect ratio is the ratio of the width to
height of a display screen
4:3 on most PCs
16:9 on high definition displays
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
80
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…
81
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
82
Dot Pitch Illustrated
Pixel
0.481 mm
83
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)
84
Colour and Displays
Pixel colour is determined by intensity
of 3 colours – Red Green Blue or RGB
 4 bits per colour

16 x 16 x 16 = 4096 colours

24 bit color (True Colour)
16.7 million colours

Video memory requirements are
significant!
85
Colour 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
86
CRT Display
87
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
88
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
Operation
1st filter polarizes light in a specific direction
Electric charge rotates molecules in liquid crystal cells
proportional to the strength of colors
Colour filters only let through red, green, and blue light
Final filter lets through the brightness of light proportional
to the polarization twist
89
Liquid Crystal Display
90
Colour Transformation Table







With 8 bits per pixel, there is no way to represent
red, green and blue colours separately
256 arbitrary combinations are chosen to form a
palette of colours
A value from 0-255 represents the colour of a
pixel
Table holds the RGB values for each of the 256
possible colours
To display a pixel, the system reads the RGB
values from the table and converts to screen
colour
With 16 bits per pixel, the table represents 64,000
colours
With 24 bits per pixel, no table is needed: 8 bits
per each RGB colour
91
Colour Transformation Table
92
Raster scan
Scanning and displaying each pixel ,
one row at a time, from left to right
 More than 30 times a second
 Interlacing

Less demanding on the monitor (each
row is displayed half as often)
Flickering

Noninterlacing (progressive scan)
93
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…
94
Interlacing Animation
Non-interlaced scanning
Interlaced scanning
Electron beam “on” (drawing)
Electron beam “off” (retracing)
95
Raster Screen Generation
96
Display: Example
97
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 up-and-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
98
Multi-scan Monitors
A multi-scan monitor can adjust to
the horizontal and vertical scan
frequencies of the video signal
produced by the interface
 Also called multi-sync, multifrequency, or variable-frequency
monitors

99
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

100
Video Frequency vs. Resolution
and Frame Rate
Video Frequency > Resolution  Frame Rate
Example:
Daewoo CMC-1703B specifications:
Video frequency = 85 MHz
Max resolution = 1280 by 1024 @ 60Hz
Note: 1280  1024  60 = 78,643,200 = 78.6 MHz
101
Printers


Output as dots (like pixels in displays)
Dots vs. pixels
300-2400 dpi vs. 70-100 pixels per inch
Dots are on or off, pixels have intensities
Intensity of dots is fixed
To create a gray scale, it is necessary to
congregate groups of dots into a single
equivalent point and print different numbers of
them to approximate different colour intensities
102
Creating a Gray Scale
103
Printers

Four main types:
Impact
Laser
Ink jet
Thermal dye transfer and thermal
wax transfer
Impact
104
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 (e.g.: carbon or NCR copies)

105
Printers

Four main types:
Dot matrix (sample impact)
Laser
Ink jet
Thermal dye transfer and thermal
wax transfer
106
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)
107
Illustration
108
Dot Matrix Print Head
One print wire
Print wires
(e.g., 12)
Front view
Side view
109
Dot Matrix Impact Printing
Paper
Print
wire
Platen
Ribbon
Paper
Side view
110
Front view
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)
111
Dot Matrix Printer: Example - 1
Specifications
• 800 cps
• 400 lpm
• 6-part forms (max)
FormsMaster 8000 by Printek, Inc.
http://www.printek.com
112
Dot Matrix Printer: Example - 2
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 @ 25% duty cycle,
35% density
Pacemaker 3410 by OKI Data, Inc.
http://www.okidata.com
113
Printers

Four main types:
Dot matrix
Laser
Ink jet
Thermal dye transfer and thermal
wax transfer
114
Laser Printer Operation
1.
2.
3.
4.
5.
6.
7.
Dots of laser light are beamed onto a drum
Drum becomes electrically charged
Drum passes through toner which then sticks
to the electrically charged places
Electrically charged paper is fed toward the
drum
Toner is transferred from the drum to the
paper
The fusing system heats and melts the toner
onto the paper
A corona wire resets the electrical charge on
the drum
115
First step

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
116
Second step
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
117
Third step
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
118
Fourth step
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
Fusing
system
119
Specifications

ppm
Pages per minute
Typically 4-10 ppm

dpi
Dots per inch
Typically 600-1200 dpi
120
Laser Printer: Example
Laserjet 5000 Series from Hewlett Packard Co.
(http://www.hp.com)
121
Printers

Four main types:
Dot matrix
Laser
Ink jet
Thermal dye transfer and thermal
wax transfer
122
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

123
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 inkfilled 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
124
attached reservoir into the firing chamber.
Inkjet Printer: Example
125
Printers

Four main types:
Dot matrix
Laser
Ink jet
Thermal dye transfer and thermal
wax transfer
126
How it works


Thermal dye transfer printers, also called dye sublimation
printers, heat ribbons containing dye and then diffuse the
dyes onto specially coated paper or transparencies. These
printers are the most expensive and slowest, but they
produce continuous-tone images that mimic actual
photographs. Note that you need special paper, which is
quite expensive. A new breed of thermal dye transfer
printers, called snapshot printers, produce small
photographic snapshots and are much less expensive than
their full-size cousins.
Thermal wax transfer printers use wax-based inks that are
melted and then laid down on regular paper or
transparencies. Unlike thermal dye transfer printers, these
printers print images as dots, which means that images must
be dithered first. As a result images are not quite photorealistic, although they are very good. The big advantages of
these printers over thermal dye transfer printers are that
they don't require special paper and they are faster.
127
Dithering
Dithering is creating the illusion of new colours and shades by varying
the pattern of dots. Newspaper photographs, for example, are dithered. If
you look closely, you can see that different shades of grey are produced by
varying the patterns of black and white dots. There are no grey dots at all.
The more dither patterns that a device or program supports, the more shades
of grey it can represent. In printing, dithering is usually called halftoning, and
shades of grey are called halftones. Example: traditional B & W newspaper.
Note that dithering differs from grey scaling. In grey scaling, each
individual dot can have a different shade of grey.
black
grey
light grey
white
128
Scanner: 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).
129
Scanners

Three main types
Flatbed
Sheet-fed
Handheld
130
Flatbed Scanner: Example
131
Sheet-fed Scanner: Example
OfficeJet Series 700 from Hewlett Packard Co
(http://www.hp.com)
132
Handheld Scanner: Example
QuickScan GP Bar Code Scanner from PSC, Inc.
(http://www.pscnet.com)
133
Pointing Devices

User Input Devices
Keyboard, mouse, light pens, graphics
tablets

Communication Devices
Telephone modems
Network devices
134
Computer Humour 
http://www.funnyhumor.com/pictures/217.php
135