Computer Peripherals

1
Computer Peripherals Part II
2
Plan

• Tape drives
• Optical disks
• Displays

3
Rationale

• Magnetic tape is used as secondary storage when
• Offline storage is acceptable or preferred
• Capacity requirements exceed that of floppy disks
• Sequential access is adequate
• Magnetic tape is used for
• Off-site data preparation
• Backup

Rev Sec 9.3 pg 256 ff
4
Terminology

• Backup
• The act of copying files to a second medium
  (typically disk or tape) as a precaution in case
  the first medium fails
• It is important in computing to backup your
  files regularly

Assumption All hard drives will eventually fail.
Rv kc
5
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

6
Reel to Reel Tape Drive
7
Tape Reels
8
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

9
Nine-track Tape Layout
Know this
Physicalrecord
Inter-recordgap
Track 1
½
Track 9
1 byte of data (8 data bits parity)
Rev Sec 9.3 pg 257
10
Tape Cartridge
11
Types of Tape Cartridges

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

12
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

13
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)

14
Plan

• Tape drives
• Optical disks
• Displays

15
Operation

• Uses light generated by lasers to record and
  retrieve information
• Information is stored by varying the light
  reflectance characteristics of the medium
• Available in read-only (CD-ROM) and read/write
  formats

Rev Sec 9.4
16
CD-ROM

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

17
Figure 9.13 Layout of a CD-ROM versus a standard
disk
18
CD-ROM vs. Magnetic Disk
CD-ROM Magnetic Disk
One spiral track (3 miles long!) Multiple tracks of concentric circles
Constant bit density 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
19
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

20
CD-ROM Drive Specs
Speed Seek Time Transfer Rate
1x 600 ms 150 KB/s
4x 135-160 ms 600 KB/s
8x 135-180 ms 1.2 MB/s
16x 100-150 ms 2.4 MB/s
24x 100-150 ms 3.6 MB/s
32x 100-150 ms 4.8 MB/s
Note These are rated values Actual values for
higher speed are typically less.
21
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

22
Pits and Lands (2 of 2)
23
CD-ROM Read Process
24
(No Transcript)
25
Laser Diodes
26
Read/Write Variations

• WORM (Write Once, Read Many)
• Magneto Optical

Rev Sec 9.3 pg 261 ff
27
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

28
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)

29
Plan

• Tape drives
• Optical disks
• Displays

30
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 sub-assembly within the box

Rev Sec 9.5 pg 262 ff
31
Figure 9.15 Layout for a display
32
Pixels
KNOW !!

• 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)

33
Figure 9.16 Display screen ratios
34
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 ( v.i.s. ?? 13.6? )

35
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)

36
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

( Learn how to do! )
37
Video RAM (KB) Per Image
Resolution Bits per pixel Bits per pixel 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
38
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
  640480, or 43
• Related terms
• Landscape
• The width is greater than the height
• Portrait
• The height is greater than the width

39
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

40
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

41
Dot Pitch Illustrated
Pixel
0.481 mm
42
Exercise Dot Pitch Image

• Q What is the dot pitch of an image displayed on
  a 19 monitor with a resolution of 1,280 by 1,024?

Skip answer
Answer
43
Exercise Dot Pitch Image
Answer

• Q What is the dot pitch of an image displayed on
  a 19 monitor with a resolution of 1,280 by
  1,024?
• A

Dot pitch 19 / 1639.2 inches 0.01159
inches 0.01159 / 0.039 mm 0.30 mm
Note Z (12802 10242)1/2 1639.2
44
Dot Pitch Image Table
Resolution Display Size Display Size Display Size Display Size 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)
45
Dot Pitch Example

• Q A 19 CRT monitor, made by Vapour Hardware
  Inc., has a dot pitch specification of 0.28 mm.
  What is the highest resolution at which this
  monitor will reliabily operate?
• A

1,280 by 1,024
Discussion Just read the value above from the
dot pitch image table. For a 19 monitor, a
1,280 by 1,024 image has a dot pitch of 0.30 mm.
The monitors dot pitch specification exceeds
this, therefore, the monitor will work fine at
this resolution. However, a 1,600 by 1,200 image
on a 19 monitor requires a dot pitch of 0.24,
which is beyond the capability of the example
monitor.
46
Exercise Dot Pitch

• Q A 17 CRT monitor has a dot pitch
  specification of 0.30 mm. What is the highest
  resolution at which this monitor may operate?
• A

Skip answer
Answer
47
Exercise Dot Pitch
Answer

• Q A 17 CRT monitor has a dot pitch
  specification of 0.30 mm. What is the highest
  resolution at which this monitor may operate?
• A 1,024 by 768

I like this question !
48
Figure 9.17 Use of a color transformation table
49
Figure 9.18 Interlaced versus noninterlaced
raster scan
50
Figure 9.19 Diagram of raster scan generation
process
51
Figure 9.20 Display example (a) desired
display, (b) video memory contents, (c) color
palette table, (d) color signals
52
Figure 9.20 (continued)
53
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

54
CRT Display
Rev Fig 9.21 pg 267 ff
55
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

56
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
57
Liquid Crystal Display
58
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

59
Interlacing Animation
Non-interlaced scanning
Interlaced scanning
60
Uses of Interlacing

• TVs use interlaced scanning
• Computer monitors (CRTs) use non-interlaced
  scanning

61
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)

62
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

63
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

Needed to accommodate different screen formats
64
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

65
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
66
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
67
NoteVaries on different systems
68
NoteVaries on different systems
Demo
69
Colour Control

• Three ways to control colour
• Selecting from a predefined palette
• Individually control red, green, and blue
• Individually control colour and brightness
• Colour is also called chrominance (C)
• Chrominance consists of hue and saturation
• Brightness is also called luminance (Y)
• Most applications support all three techniques

Next 2 slides
70
Predefined Palette
71
Custom Control
Demo
72
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

73
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

74
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

75
VGA/SVGA/XGA Pinouts
Pin 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
76
S-video Pinouts
Pin Signal
1 Ground
2 Ground
3 Y (luminance)
4 C (Chrominance)
4-pin mini-DIN connector
77
Flat Panel Displays

• A very thin display screen
• Most flat panel displays use LCD technology
• Other technologies
• ELD (electro-luminescent display)
• Gas plasma display

78
Active-Matrix Display

• A type of liquid crystal display in which the
  image is refreshed more frequently than in
  conventional (passive matrix) displays
• Most common type of active-matrix display is
  known as TFT (thin-film transistor)
• The terms active matrix and TFT are used
  interchangeably

79
Thank you