44 What are MDA, Hercules, CGA and EGA adapters?
Description
This article is from the comp.sys.ibm.pc.hardware.video Frequently Asked Questions, by Michael Scott with numerous contributions by others. (v1.0).
44 What are MDA, Hercules, CGA and EGA adapters?
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 with a horizontal refresh of 18.43 kHz. 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.
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?".
Continue to:
My Books
