Video Standards

Hercules (MDA)

CGA Colour Graphics Adapter

MDA (Hercules)

Monochrome Display Adapter

MDA was the original display adapter on the IBM PC. Technically, it was a character mapped system. It was only capable of 256 special characters in set positions on the screen. It is not capable of pixel-by-pixel control. It was ideal for simple DOS based applications with no graphics, like word processing. As a plus, IBM included an integrated printer port, thereby saving another slot.

MDA pin out	Pin	Description
	1	Ground
	2	Ground
	3	Not used
	4	Not used
	5	Not used
	6	Intensity
	7	Mono video
	8	Horizontal Sync
	9	Vertical Sync

CGA Colour Graphics Adapter

Video Type: TTL, 16 colours

AKA: IBM RGBI

A few months after the release of MDA, the CGA adapter came out. It worked with an RGB monitor and worked off the test mapped method. This allowed pixel-by-pixel control. It could also display 16 colours, 4 at a time, on a 320 x 200 display. The pixels are quite large and the resolution was poor, but it could do graphics. CGA offered a high resolution mode of 640 x 200, but then it could only do two colours. Besides its limitation, this card remained very common for quite a while. It had a couple of annoyances, which were flicker and snow.

CGA used a digital signal, referred to as TTL (Transistor - Transistor Logic), for the transmission of its video signal.

CGA Pin Out

640 x 200, 15.7Khz, 60Hz

	Pin	Description
	1	Ground
	2	Ground
	3	Red
	4	Green
	5	Blue
	6	Green Intensity
	7	Blue Intensity
	8	Horizontal Sync
	9	Vertical Sync