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From: mcdonald@aries.scs.uiuc.edu (Doug McDonald)
Newsgroups: comp.windows.ms
Subject: Re: What really limits video speed?
Message-ID: <1990Dec16.233738.28520@ux1.cso.uiuc.edu>
Date: 16 Dec 90 23:37:38 GMT
References: <4145@mindlink.UUCP>
Sender: news@ux1.cso.uiuc.edu (News)
Organization: School of Chemical Sciences, Univ. of Illinois at Urbana-Champaign
Lines: 30

In article <4145@mindlink.UUCP> a516@mindlink.UUCP (Jordan Melville) writes:
>> pti4378@ritvax.isc.rit.edu writes:
>> I am running win3 on someone's 16 Mhz 386SX with a 512K Paradise board at
>> 640x480x256.  The video speed is (as many have pointed out) rather slow with
>> the 256 color driver.
>> 
>> I would like to know whether it is the speed of the CPU, the video board, or
>> the video driver that is the "weak link".  i.e., if I were to buy a different
>> system, what would be the best component to improve upon to increase video
>> speed?
>
>The reason it's so much slower, is because Windows has twice as much graphical
>information to worry about. 16 colours only needs 4 bits, whereas to you need 8
>bits to create each pixel of colour on a 256 colour plane. This doubles the
>video memory overhead, and doubles the amount of work Windows has to do to show
>any information. It's a trade off, you just have to decide what you need more.
>

Comparing 16 color VGA to 256 color VGA is **NOT** as simple as saying that
there are twice as many bits. This is beacuse for the 256 color modes
you MUST convey all 8 bits for every pixel. Due to the bit-plane
design of the EGA/VGA in some cases - particularly text and simple
lines - you can convey the information for up to 8 pixels in
8 bits. This is eight times faster.

The EGA/VGA is a brilliant design. Really. Whoever decided how 
the architecture worked was a real great guy. Whoever DOCUMENTED
it for IBM must have been a real dildohead. 

Doug McDonald