Monochrome Display Adapter (MDA)

  The MDA is one of the original video systems shipped with the IBM-PC
  circa 1981.  It has been mostly replaced by EGA, VGA, and SVGA systems.
  TECH Help! covers the following MDA and general video topics:

   Video Services ..... INT 10H video services
   Video Modes ........ includes MDA modes

   Video Memory Layouts accessing MDA video memory
   BIOS Data Area ..... includes video-specific variables in low memory

   Screen Attributes .. codes determine "colors" for text mode

   CGA I/O Ports ...... I/O port addresses; video controller registers
   MDA Pin Outs ....... connectors on MDA cards

   INT 1dH ............ video initialization table

  The MDA provides NO graphics support and is limited to a single text mode
  (80x25).  Its video memory begins at b000:0000 and it supports only one
  "page" of video.

  A popular variant known as Hercules and MonoGraphics also exists.  These
  versions do support a 720x348 2-color graphics mode and they work with
  the same low-cost video display as the MDA.

█▌Testing for an MDA▐█
  Use INT 11H (equipment list) and check bits 4 & 5.  If (w AND 30H) is 30H,
  then you are running on an MDA or compatible and video memory begins at
  b000:0; otherwise, its a CGA, EGA, VGA or other color system (text-mode
  video memory begins at b800:0).

See Also: CGA
          CGA I/O Ports
          Video Memory Layouts