Computer Peripherals

1
Lecture 9-10
ITEC 1000 Introduction to Information Technology

• Computer Peripherals

Prof. Peter Khaiter
2
Lecture Template

• Peripherals
• Storage Devices
• Displays
• Printers
• Scanners
• Pointing Devices

3
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

4
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)

5
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

6
Storage Hierarchy
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)
7
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)

8
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)

9
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

10
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)

11
Magnetic Disks

• 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

12
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)

13
Floppy Disk Example
Shutter
Access window
Cutawayshowing disk
Spindle
Case
Writeprotect tab
14
Hard Disks

• 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)

15
Hard Disks Example
Top view of a 36 GB, 10,000 RPM, IBM SCSIserver
hard disk, with its top cover removed, 10 stacked
platters(The IBM Ultrastar 36ZX)
16
Winchester Disks

• 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)

17
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/
18
Hard Disk Layout
Head
Block
Headmotor
Platter
Sector
Track
Cylinder
Track
Drivemotor
Head, onmoving arm
Head assembly
19
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

20
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)

21
Hard Disk Terminology

• Sector
• That portion of a track falling along a
  predefined pie-shaped 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)

22
Locating a Block of Data
Seek Time
Latency Time
Transfer Rate
Latency
Transfer
Head
Seek
Desiredtrack
Note Access time seek time latency
23
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

24
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

25
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
26
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

27
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 7200 x 30 216,000 sectors/min
• 216,000 x 0.5 108,000 Kbytes/min
• 108,000 / 60 1,800 Kbytes/s
• 1,800 / 210 1.76 Mbytes/s

28
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
29
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
30
Typical Specs
31
Track Format

• Format of each track

gap
gap
data
header
CRC
32
Disk Block Formats
Single Data Block
Header for Windows disk
33
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

34
Disk Controller

• Interface between the disk drive and the system
  is known as a disk controller
• 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

May also require special driver, as in CD-ROMs
35
Buffering
Example Reading data from a disk
System
Diskcontroller
Disk
RAM
Buffer (RAM)
36
Multi-block Transfers (1 of 2)

• 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

37
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

38
Magnetic Disks

• Data Block Format
• Interblock gap
• Header
• Data
• Formatting disk
• Disk Interleaving
• Disk Arrays
• RAID mirrored, striped
• Majority logic ? fault-tolerant computers

Disk Interleaving
39
Interleaving

• 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

40
Interleaving Examples
Factor
2
1
3
5
4
6
8
7
9
11
etc.
1
2
3
4
5
21
etc.
1
2
3
31
etc.
41
21 Interleaving
2
6
1
7
5
3
9
8
4
42
File System Considerations

• 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

43
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

44
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

45
Fixed heads

• Fewer tracks but eliminates seek time

Moving head
Disk
Spindle
Fixed heads
46
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)

47
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

48
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

49
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

50
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

51
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

52
Magnetic Tape

• 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 (21 compression)

53
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

54
Reel to Reel Tape Drive
55
Tape Reels
56
Tape Reel Specifications

• 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

57
Nine-track Tape Layout
Physicalrecord
Inter-recordgap
Track 1
½
Track 9
1 byte of data (8 data bits parity)
58
Tape Cartridge
59
Types of Tape Cartridges

• QIC (Quarter Inch Cartridge)
• DAT (Digital Audio Tape)

60
QIC (Quarter Inch Cartridge)

• 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

61
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)

62
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

63
CD-ROM

• CD-ROM stands for compact disc, read-only
  memory
• Evolved from audio CDs
• Disk size 120 mm (5¼)
• Capacity 550 MB

64
CD-ROMs
65
Layout CD-ROM vs. Standard Disk
Hard Disk
CD-ROM
66
CD-ROM vs. Magnetic Disk
67
CD-ROM Data Organization

• 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

68
Optical Storage

• Laser strikes land light reflected into
  detector
• Laser strikes a pit light scattered

69
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

70
Pits and Lands (2 of 2)
71
CD-ROM Read Process
72
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

73
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)

74
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

75
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 BW (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)

76
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? )

77
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)

78
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

79
Video RAM (KB) Per Image
See previous slide for calculations
80
Aspect Ratio

• Aspect ratio is the ratio of the width to height
  of a display screen
• 43 on most PCs
• 169 on high definition displays
• For a 640 by 480 display, the aspect ratio is
  640480, or 43
• Related terms
• Landscape
• The width is greater than the height
• Portrait
• The height is greater than the width

81
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

82
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

83
Dot Pitch Illustrated
Pixel
0.481 mm
84
Dot Pitch Image Table
Note Dot pitch figures in mm (millimeters)
85
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!

86
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

87
CRT Display
88
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

89
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

90
Liquid Crystal Display
91
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

92
Colour Transformation Table
93
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)

94
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
• Lets see

95
Interlacing Animation
Non-interlaced scanning
Interlaced scanning
96
Raster Screen Generation
97
Display Example
98
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

99
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, multi-frequency, or
  variable-frequency monitors

100
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

101
Video Frequency vs. Resolution and Frame Rate
Video Frequency gt Resolution ? Frame Rate
Example Daewoo CMC-1703B specifications
Video frequency 85 MHz Max resolution
1280 by 1024 _at_ 60Hz Note 1280 ? 1024 ? 60
78,643,200 78.6 MHz
102
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

103
Creating a Gray Scale
104
Printers

• Four main types
• Impact
• Laser
• Ink jet
• Thermal dye transfer and thermal wax transfer

105
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)

106
Printers

• Four main types
• Dot matrix (sample impact)
• Laser
• Ink jet
• Thermal dye transfer and thermal wax transfer

107
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)
108
Illustration
109
Dot Matrix Print Head
Print wires (e.g., 12)
Front view
110
Dot Matrix Impact Printing
Paper
111
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)

112
Dot Matrix Printer Example - 1

• Specifications
• 800 cps
• 400 lpm
• 6-part forms (max)

FormsMaster 8000 by Printek, Inc. http//www.print
ek.com
113
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 _at_ 25 duty cycle, 35 density

Pacemaker 3410 by OKI Data, Inc. http//www.okidat
a.com
114
Printers

• Four main types
• Dot matrix
• Laser
• Ink jet
• Thermal dye transfer and thermal wax transfer

115
Laser Printer Operation

• 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

116
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.

117
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
118
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
119
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.
120
Specifications

• ppm
• Pages per minute
• Typically 4-10 ppm
• dpi
• Dots per inch
• Typically 600-1200 dpi

121
Laser Printer Example
Laserjet 5000 Series from Hewlett Packard
Co. (http//www.hp.com)
122
Printers

• Four main types
• Dot matrix
• Laser
• Ink jet
• Thermal dye transfer and thermal wax transfer

123
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

124
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.

125
Inkjet Printer Example
126
Printers

• Four main types
• Dot matrix
• Laser
• Ink jet
• Thermal dye transfer and thermal wax transfer

127
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
  photo-realistic, 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.

128
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.
129
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).

130
Scanners

• Three main types
• Flatbed
• Sheet-fed
• Handheld

131
Flatbed Scanner Example
132
Sheet-fed Scanner Example
OfficeJet Series 700 from Hewlett Packard
Co (http//www.hp.com)
133
Handheld Scanner Example
QuickScan GP Bar Code Scanner from PSC,
Inc. (http//www.pscnet.com)
134
Pointing Devices

• User Input Devices
• Keyboard, mouse, light pens, graphics tablets
• Communication Devices
• Telephone modems
• Network devices

135
Thank you!
Reading Lecture slides and notes, Chapter 10
http//www.funnyhumor.com/pictures/217.php