Monochrome Display Adapter
First video card used on a PC, launched with the very first IBM PC. It didn’t allow graphics and colors, only text. It usually had a parallel port attached. After some time video card manufacturers started manufacturing “dual” video cards, which were MDA and CGA at the same time, selectable thru a jumper and also allowing Hercules (HGC) mode. See the pictures below where we posted an original MDA video card and a “dual” video card. You can easily tell which one is which because of the size.
MDA video card used a 9-pin female D-shell connector.
Notice that you need to install a MDA video monitor together with a MDA video card. It doesn’t work with other monitor types, like CGA, EGA, VGA, SuperVGA, etc. MDA video monitor is different from CGA video monitors (different resolutions). Don’t think that a CGA video monitor will work on a MDA video card only because they use the same plug and because the CGA video monitor you’ve got is monochromatic.

Figure 1: Original MDA video card.

Figure 2: "Dual" video card, which is a CGA/MDA/Hercules combo.