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