A Guide to PC Hardware Maintenance and Repair

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Chapter 15 Your Computer and Graphics
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Objectives

• To learn how images are formed on monitor screens
• To learn the basics of video card specifications
• Examine some of the techniques used to simulate
  3D on a monitor
• Look at some of the other graphics devices.

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Computer Monitors

• Cathode Ray Tube (CRT)
• Old technology thats still alive and well
• Liquid Crystal Display (LCD)
• Flat panel technology thats easy on the eyes

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CRT Monitors

• Based on the same design as a television tube
• Not very energy efficient and they take up a lot
  of space
• But theyre CHEAP!!!

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The Parts of the CRT

• Electron Guns (cathodes)
• Deflection Yoke
• Shadow Mask
• Phosphor Layer

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How the CRT Makes an Image

• Three electron guns, one for each primary color
  emit a beam of electrons
• The deflection yoke causes the electron beam to
  scan across the phosphor surface
• The shadow mask makes sure the gun controlling
  blue hits the blue layer, etc.
• When the electrons hit the phosphorous, it glows

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Making Millions of Colors from 3

• The primary colors are red, green and blue
• One phosphor of each color creates a triad
• How strong the electron beam is when it strikes
  the phosphorous determines how brightly each
  primary color glows
• The three colors together create the hues you see

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Each color in the triad can glow in a number of
intensities that is determined by how many bits
controls that color
3 dots that can attain 256 different levels of
intensity each can create 2563 colors.
A color controlled by 8 bits can attain 28, or
256 different color intensities
2563 16,777,216 mathematically unique hues.
Good luck seeing them all.
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Some Monitor Terms

• Pixel
• Dot Pitch
• Raster Line
• Horizontal Refresh Rate
• Vertical Refresh Rate

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Pixel

• A single dot of color displayed on the monitor
• Size of pixel determined by monitor size and
  resolution setting
• It may or may not be the same as a triad
• It may occupy multiple triads and it may occupy
  partial triads

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Dot Pitch

• The distance between two like-colored phosphors
  on the screen
• Some less reputable manufacturers offer dot pitch
  ratings based on the distance between two
  adjacent phosphors.

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Raster Line

• A single line of pixels running from left to
  right on the monitor
• The number of raster lines will equal the
  vertical resolution of the display
• For example, on a display set to 640x480
  resolution, there are 480 raster lines.

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Horizontal Refresh Rate

• The time it takes to draw a single raster line on
  the display and return to the beginning of the
  next line
• Generally measured in megahertz

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Vertical Refresh Rate

• The time it takes to draw a complete screen from
  top to bottom and left to right
• Generally measured in hertz
• This is the measurement that determines if the
  monitor is ergonomically comfortable

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LCD Monitors

• Consume far less electricity than CRT monitors
• Are easier on the eyes over long periods of time
• Somewhat costlier, although they are dropping in
  price

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Four types of LCDs Used Today

• Common Plane
• Passive Matrix
• Active Matrix
• Also called Thin Film Transistor (TFT)
• Plasma

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Common Plane LCDs

• Either monochromatic or using very few colors
• Must be backlit
• Used on watches, hand-held games and PDAs

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Passive Matrix

• Somewhat slow for high-quality displays
• Was commonly used on budget laptop computers
• Has generally been left by the wayside

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Active Matrix or TFT

• Capable of faster refresh rates and higher
  resolutions
• Accepted as one of the best types of displays for
  laptop computers and small televisions
• Somewhat costly

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Plasma

• Extremely high-quality
• Used primarily in high-end applications, such as
  High-definition TV
• Suffers from a half-life. Good for about seven
  years, but degrades in quality rapidly after that.

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Graphics Adapters

• These are the devices that actually create the
  image you see
• Can appear as expansion devices installed in a
  slot on the motherboard
• Can also be built onto the motherboard

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Primary Components of a Video Card

• Random Access Memory Digital/Analog Converter
  (RAMDAC)
• The Video Chipset
• Video Memory

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The RAMDAC

• The microprocessor that controls the card
• General range of speeds is between 250 and 800Mhz
• Speed of video card is dependent on speed of
  RAMDAC as long as all other components can keep
  up.