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10. Computer Peripherals – Part II. Chapt. 10. Plan. Tape drives Optical disks Displays. 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

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Plan

  • Tape drives

  • Optical disks

  • Displays


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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


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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”


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Types of Tape Drives

  • Two types:

    • Reel-to-reel

      • Used on mainframe computers

    • Cartridge

      • 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




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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

  • Datadensity/capacity

    • 1600 frames/inch  2400 x 12 x 1600 = 46,080,000 bytes/reel

    • 6250 frames/inch  2400 x 12 x 6250 = 180,000,000 bytes/reel


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Nine-track Tape Layout

Physicalrecord

Inter-recordgap

Track 1

½”

Track 9

1 byte of data

(8 data bits + parity)



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Types of Tape Cartridges

  • QIC (Quarter Inch Cartridge)

  • DAT (Digital Audio Tape)


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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


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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)


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Plan

  • Tape drives

  • Optical disks

  • Displays


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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


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CD-ROM

  • CD-ROM stands for “compact disc, read-only memory”

  • Evolved from audio CDs

  • Disk size: 120 mm (5¼”)

  • Capacity: 550 MB



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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



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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

  • 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


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Land

Pit

Reflectedlight

Scatteredlight

Laser

Laser

Laser

Pits and Lands (2 of 2)


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Land

Pit

Transparent

protective layer

Prism

Light detector

Laser

diode

More detail

CD-ROM Read Process



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Read/Write Variations

  • WORM (Write Once, Read Many)

  • Magneto Optical


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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 CR-ROMs manufactured


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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)


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Plan

  • Tape drives

  • Optical disks

  • Displays


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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


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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


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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



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Operation of an LCD

  • Two sheets of polarizing material with a liquid crystal solution between them

  • An electric current passes through the liquid, causing 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



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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)


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15”

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


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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)


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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


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Video RAM (KB) Per Image

See previous slide for calculations


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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


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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…


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Dot pitch = 15 / 800 inches

= 0.01875 inches

= 0.01875 / 0.039 mm

= 0.481 mm

Notes:

Z

480

  • Z = (6402 + 4802)1/2 = 800

  • 1 mm = 0.039 inch

640

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:


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Dot Pitch Illustrated

Pixel

0.481 mm


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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


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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


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Dot Pitch Image Table

Note: Dot pitch figures in mm (millimeters)


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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 reliably 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 monitor’s 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.


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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


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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


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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…


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Electron beam “on” (drawing)

Electron beam “off” (retracing)

Interlacing Animation

Non-interlaced scanning

Interlaced scanning


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Uses of Interlacing

  • TVs use interlaced scanning

  • Computer monitors (CRTs) use non-interlaced scanning


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Horizontalretrace

Verticalretrace

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)


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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


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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


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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


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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


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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


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Note:Varies on different systems


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Note:Varies on different systems

Demo


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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




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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


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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


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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


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VGA/SVGA/XGA Pinouts

DE15 connector


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S-video Pinouts

4-pin mini-DIN connector


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Flat Panel Displays

  • A very thin display screen

  • Most flat panel displays use LCD technology

  • Other technologies

    • ELD (electro-luminescent display)

    • Gas plasma display


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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


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Thank you

Next topic


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