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From: jpn@genrad.com (John P. Nelson)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Dual Monitor hook up
Message-ID: <40737@genrad.UUCP>
Date: 11 Feb 91 18:19:20 GMT
References: <26754@uflorida.cis.ufl.EDU> <NELSON.91Feb7124258@sun.clarkson.edu> <26775@uflorida.cis.ufl.EDU> <2128@umriscc.isc.umr.edu>
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Reply-To: jpn@maxwell.genrad.COM (John P. Nelson)
Organization: GenRad, Inc., Concord, Mass.
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>I *think* it said that most programs don't really use the 16-bit bus
>there is actually little difference when switching between the 2 setups.  I
>think windows is one of the ones that uses only the 8-bit mode.  If someone
>could dig up the article, it might shed some more light on this.

I think the point is that in normal VGA graphics modes, the VGA
architecture restricts accesses to 8 bits at a time, anyway.  The main
thing sped up by a 16 bit display card is the video BIOS.  While it is
possible to write to the video memory in TEXT mode 16-bits at a time,
this is not really that noticable since this is not normally a
noticable bottleneck.

While you may be able to write a 16 bit word to a VGA in graphics mode,
it really takes as long as two 8 bit cycles because of the architecture
of the VGA controller.

Of course, it is possible that if super-VGA drivers are included with a
16-bit card, that they write to the video memory in graphics modes
16-bits at a time in a proprietary manner.

     john nelson

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