Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!tut.cis.ohio-state.edu!pt.cs.cmu.edu!b.gp.cs.cmu.edu!Ralf.Brown@B.GP.CS.CMU.EDU
From: Ralf.Brown@B.GP.CS.CMU.EDU
Newsgroups: comp.sys.ibm.pc
Subject: Re: Why no graphics in text mode?
Message-ID: <25b5c340@ralf>
Date: 18 Jan 90 12:23:12 GMT
Sender: ralf@b.gp.cs.cmu.edu
Organization: Carnegie Mellon University School of Computer Science
Lines: 20
In-Reply-To: <26036@cup.portal.com>

In article <26036@cup.portal.com>, cliffhanger@cup.portal.com (Cliff C Heyer) wrote:
}Also, the AT bus is slow enough to make writing
}bit maps to the video adaptor slow. On (expensive)
}workstation platforms the bus has 10 times the
}bandwidth so this is not a problem.

As it happens, the bottleneck is not the AT bus (which can easily handle
5 megabytes per second), but the video memory on the video board!  Because
systems in use today have to lock out the CPU while the video circuitry is
reading the video memory, most video boards can only allow the CPU one access
every 1.1 to 1.5 microseconds.	On my 386/33, this translates to 47 wait
states!  Add to this the fact that many EGA and VGA graphics modes require
bank-switching to get at all the video memory used by an image.
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"How to Prove It" by Dana Angluin              Disclaimer? I claimed something?
14. proof by importance:
    A large body of useful consequences all follow from the proposition in
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