CRT
  CRT - cathode ray tube

  Electron beam that causes a phosphor coated surface to glow.

  Phosphors created as dots (pixels)

  Color - generates most possible colors.
    Three colors - blue (cyan), red (magenta), green.

  Monochrome - only a single color but of different shades.
    White or green or yellow.
    Generally obsolete.

  By varying the intensity of the electron beams,
    Colors and brightness are created

  Dot pitch - Closeness (size) of each set of pixels.
    Determines clarity and possible resolution of display.


Raster
  Raster scan
    Data converted into a series of rows of dots.
    Each line of dots is passed in sequence.

  Refresh
    Phosphor pixels fade very quickly.

    Allowing a new changed image to be displayed.

    Screen has to be refreshed repeatedly to keep an image.

  Total refresh time
    Time to draw each line on screen.

    Time to retrace (reposition) electron gun to start of next line.
      (horizontal sync).

    Time to retrace electron gun back to top of screen.
      (Vertical sync).


Interlacing
  Ways screen is redrawn
   Interlaced - spits data into alternate images.
     Low bandwidth or throughput - less data per second.
     Faster refreshes or more color depth.
     Generally not comfortable for static images.
     Economical equipment.
   Non-Interlaced - all data sent in sequence.
     Higher throughput
     Slower refreshes or less color depth.
     Faster refresh more comfortable.
     More expensive equipment.


Resolution
  Number of dots per line x number of lines per screen.
  Generally 4:3 ratio.
  Common resolutions.
   640 x 480 - 307,200 pixels.
   800 x 600 - 480,000 pixels.
  1024 x 768 - 786,432 pixels.
  1280 x 1024 - 1,310,720 pixels.
  1600 x 1200 - 1,920,000 pixels.
  Higher resolution requires faster circuits for higher refresh.
  Monitors may be fixed resolution or limited.
  Resolution matching and overdriving crt.


Color depth
  Color depth not determined by crt - color choices infinite.
  Color depth determined by video card (interface).
  However, color depth affects the quantity of data transferred to crt.
  4 bit - 16 colors
   Basic solid colors for emphasis.
   With careful design, images have some depth.
  8 bit - 256 colors
    Palette - 256 selected colors from 16 million colors.
  16 bit - 65536 colors - high color.
   5 bits red, 6(5) bits green, 5 bits blue.
   Reasonably true color representation.
  24 bit - 16 Meg - true color.
    8 bits for each color (256 intensity levels for each color).


Refresh rates.
  60 Hz - noticeable by most people and stressful.
   Low data throughput.
   Allows maximum color depth and higher resolutions.
  >60 Hz & < 72 Hz - noticeable by some people.
  72 Hz - a few people may notice flicker.
  > 72 Hz - very few people notice.
   High data throughput.
   video card may limit color depth and resolution.
  > 100 Hz - Not detectable by humans.
  Beware of over-driving.


Graphics vs text
  Text mode - data represents text arranged in a grid of characters.
   Screen is usually 80 characters x 25 lines.
   Character unit represented by two bytes of memory
      1 byte ascii values.
      1 byte used for attribute (bright, blinking).
  Two byte code interpreted by video card to generate bit image.
      8x14 dot array for each character
      14 bytes (bit mapped, no attributes) vs 2 bytes (generated).
  Graphics mode - each bit on screen individually mapped.
   Resolution.
   Color depth.
  100 fold increase in data.


Throughput
  Common resolutions in true color.
   640 x 480 - 307,200 pixels * 3 bytes/pixel * 72 Hz = 66,355,200
   800 x 600 - 480,000 pixels -> 104 MB/sec.
  1024 x 768 - 786,432 pixels -> 170 MB/sec.
  iv. 1280 x 1024 - 1,310,720 pixels -> 283 MB/sec.
  v. 1600 x 1200 - 1,920,000 pixels -> 415 MB/sec (5.76MB * 72Hz).
  Video cards equipped with their own high speed memory.
  Data moved from main memory to video memory.
  Accelerators are circuits that can generate a graphics image based
  on a smaller symbol transferred from main memory.
    Windows symbols and objects
    Standard images - circle, sphere, cubes.


Adaptors - legacy
  MDA - Monochrome Data Adaptor
   720x350 dots, 80 x 25 characters, 9 x 14 dot character, 50 Hz
  Hercules Graphics Card
   Provided bit mapping for MDA type display.
  CGA - Color Graphics Adaptor
   80 x 25 x 16 color text mode - 8x8 dot characters.
   640 x 200 monochrome graphics - 160 x 200 x 16 color.
  Digital transmission to monitor.
  EGA - Enhanced Graphics Adaptor.
   Graphics 640x350 with 16 colors selected from 64 possible.
   80x25 text mode with 16 colors.
  60 Hz refresh.
  iv. Digital transmission to monitor.


Adaptors - current VGA
  VGA - video graphics adaptor.
   Standard outlined by IBM.
   640x480 dots x 16 color.
  320x200 dots x 256 colors.
  iv. Colors chose from a palette of 262,144 possible colors.
  v. Analog signal to monitor.
  vi. Not used except when in safe mode.
  vii. But all video cards are designed to go into this mode.


Adaptors - SVGA
   SVGA - super video graphics adaptor
   Non-standard - each manufacturer offers different features.
   Monitors need adjustments to better match cards.
   800 x 600
   Need software drivers to match card to system.
   Provides vga mode.
   Current cards(chip sets) provide 1024x768 and up.
   High speed memory on card to handle data throughput.


VESA standard
  8514/A - an IBM standard competing with VGA
   Offered higher resolution, color and some acceleration.
   But proprietary to IBM and used interlaced mode.
  XGA - Extended Graphics Array - another IBM Standard
   PS/2 machines, bus mastering and up to 1 Meg Vram.
   Better resolution than VGA.
  VESA - Video Electronics Standards Association (NEC)
   Outlined a standard for SVGA cards and above.
   Called VBE - Video bios extension - standard set of functions.
      Either implemented in hardware
      Or in the cards software drivers.
  Originally ignored, many video card makers now try to follow.