Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rosen
From: rosen@cs.utexas.edu (Eric Carl Rosen)
Newsgroups: comp.sys.mac.hardware
Subject: Re: IIsi RAM cache setting, performance...
Message-ID: <1547@nada.cs.utexas.edu>
Date: 14 Jun 91 05:05:18 GMT
References: <1991Jun11.161138.31376@kuhub.cc.ukans.edu> <31570001@hpcuhe.cup.hp.com>
Organization: Dept of Computer Sciences, UTexas, Austin
Lines: 19

>So why is 256-color mode slower than 16-color mode, then?  It seems that
>16-color mode would reserve less memory, making it more likely that you
>program would be running out of the slow memory.

Probably becase in 16-color mode, redrawing the screen takes less time than
in 256-color mode since less memory needs to be written.

In 16-color mode, 640x480 pixels x 4 bits/pixels = 150 KB.
In 256-color mode, 640x480 pixels x 8 bits/pixels = 300 KB.

If all things were equal (which they aren't, I imagine, since dealing with
full bytes is more efficient than half-bytes), you would thus expect redrawing
a 16-color screen to take half the time that redrawing a 256-color screen
would require.

So, apparently the slowdown experienced from drawing in 256-color mode is
more than offset by running your program out of the faster RAM above 1 MB.

--Eric