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  Now we come to the inner workings of the video buffer map. In this
  section, we'll see how the information in the video memory is related to
  the display screen.

  Although the video buffer memory map varies according to the video mode
  you use, a clear family resemblance exists among the video modes. In text
  modes, the video buffer map in all IBM video subsystems is the same. In
  graphics modes, there are two general layouts, a linear map based on the
  map used with the original CGA graphics modes and a parallel map that was
  first used in EGA graphics modes.

  Video Mode     Starting       Memory Used   Subsystem
                 Paragraph      (bytes)
                 Address (hex)
  --------------------------------------------------------------------------
  00H, 01H       B800H             2000       CGA, EGA, MCGA, VGA
  02H, 03H       B800H             4000       CGA, EGA, MCGA, VGA
  04H, 05H       B800H           16,000       CGA, EGA, MCGA, VGA
  06H            B800H           16,000       CGA, EGA, MCGA, VGA
  07H            B000H             4000       MDA, EGA, VGA
  0DH            A000H           32,000       EGA, VGA
  0EH            A000H           64,000       EGA, VGA
  0FH            A000H           56,000       EGA, VGA
  10H            A000H          112,000       EGA, VGA
  11H            A000H           38,400       MCGA, VGA
  12H            A000H          153,600       VGA
  13H            A000H           64,000       MCGA, VGA
  --------------------------------------------------------------------------

  Figure 4-10.  Video buffer addresses in IBM video modes.

  Before we examine the actual map of the video buffer, let's look at the
  addresses where the video buffer is located. (See Figure 4-10.) The
  breakdown is straightforward: Color text modes start at paragraph address
  B800H, and monochrome text mode starts at B000H. CGA-compatible graphics
  modes start at B800H. All other graphics modes start at A000H. The amount
  of RAM required to hold a screenful of data varies according to the number
  of characters or pixels displayed, and, in the case of graphics modes,
  with the number of bits that represent a pixel.