| What are MDA, Hercules, CGA and EGA adapters?
|Are the acronyms confusing? try the
Glossary of computer terms
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Monochrome Display Adapter (MDA)
This was the first display adapter shipped with the IBM PC, and
was only capable of displaying text, at an effective pixel addressability
of 720x350. The MDA provides crisp monochrome text at a low vertical
refresh rate of 50 Hz, and a 18.43 kHz horizontal refresh rate.
Hercules Graphics Card
This adapter, introduced by Hercules Computer Technology, Inc.,
provided MDA compatibility and extensions for graphics at 720x348 pixel
addressability. Due to its popularity, several other vendors released cards
with Hercules compatibility modes, but unfortunately few are 100% compatible.
Color Graphics Adapter (CGA)
The CGA, released by IBM, supports 4 colours in graphics mode and
8 in text mode at a pixel addressability of 640x200. The CGA provides a
vertical refresh of 60 Hz (200 lines) with a horizontal refresh of 15.75
kHz (640 pixels.) This
limited pixel addressability results in text which is considerably worse
than that provided by the MDA. An additional problem is that processor
access to the CGA interferes with screen refreshes, causing 'snow' on the
monitor. This results in an irritating flicker in some programs.
Characters in 8x8 pixel matrix. Hs, Vs, and RGBI all TTL levels.
Enhanced Graphics Adapter (EGA)
The next offering by IBM has a pixel addressability of 640x350
and offers the display of 16 colours out of a palette of 64. It offers
backwards compatibility with the CGA. EGA displays (Enhanced Colour
Displays) have a 60 Hz vertical refresh rate and horizontal refresh rates
of 15.75 or 21.8 kHz.
For information on which displays are compatible with which adapters,
refer to "What monitors will work with my MDA/Hercules/CGA/EGA card?".