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From: avenger@runx.ips.oz (Troy Rollo )
Newsgroups: comp.sys.atari.st,comp.sys.apple,comp.sys.mac,comp.sys.ibm.pc
Subject: Re: VGA, EGA, CGA: what is the difference?
Message-ID: <2023@runx.ips.oz>
Date: 26 Feb 89 03:24:38 GMT
References: <4306@psuvax1.cs.psu.edu>
Organization: RUNX Un*x Timeshare.  Sydney, Australia.
Lines: 37

> 
> Can any netter tell me what differecnce VGA, EGA and CGA make and what
> 'campatible to VGA and EGA' implies?
> 
	CGA = Colour graphics adapter.
	Likje a monochrome display adapter with 160x100 16 colour,
320x200 4 colour and 640x200 monochrome graphics. Colour registers
exist on CGA and EGA with 6 bits for each colour which define the physical
colour displayed for a given colour number.

 	EGA = Enhanced graphics adapter
	Can emulate a CGA to an extent - some clone boards emulate CGA
properly - as well as a 640x350 monochrome, 640x350 16 colour. Text is
much easier to read on EGA than CGA

	VGA = Video Graphics Adapter
	Can emulate EGA and CGA - most can do so fully. Some also emulate
MDA and Hercules. Ideally you should try to get one which has full register
level downward compatibility with CGA and EGA. Text modes are enhances by adding
an extra 50 scan lines (350->400), and there are 3 new graphics modes -
640x480 2 colour, 640x480 16 colour and 320x200 256colour. There are 64
... oops 256 colour registers each with 24 bits, although only 18 bits are
used, with 256000 possible colours and shades. Most modes can take advantage
of this. Some cards have additinal modes including:
    132x44 text, 132x25 and 132x28 all with 4 colours
    1056x352, 1056x350, 1056x364 all 16 colours
    640x40 800x600 256 colours
    024x768 16 colours

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