Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!zaphod.mps.ohio-state.edu!cis.ohio-state.edu!tut.cis.ohio-state.edu!ucbvax!agate!juliet!c164-al
From: c164-al@juliet.uucp (Joon Song)
Newsgroups: comp.windows.ms
Subject: Re: Why can't I use 640x480x256 mode
Message-ID: <1991May19.223327.11312@agate.berkeley.edu>
Date: 19 May 91 22:33:27 GMT
References: <1991May19.090016.15758@agate.berkeley.edu>
Sender: root@agate.berkeley.edu (Charlie Root)
Reply-To: c164-al@juliet.UUCP (Joon Song)
Organization: University of California, Berkeley
Lines: 24

In article <1991May19.090016.15758@agate.berkeley.edu> gunjan@garnet.berkeley.edu (Gunjan Bhow) writes:

>I run Windows 3.0 in 386 Enh  mode.
>
>Till now, I was running 800x600x16 resolution. (my vga has 256K memory) 
>and using the "win3_16f.exe" driver from cica. No problem so far.
>
>I read somewhere that with 256k, i can also use the 640x480x256 resolution.
>Since I had lots of .bmp files in this resolution and they looked much nicer
>than their dithered 800x600x16 counterparts, i decided to give this new  
>resolution a try. 

If your VGA card only has 256K of memory, you CAN NOT display 640x480x256.
The maximum resolution at which you can display 256 colors is 640x400x256.

The reason for this is very simple.  Each pixel in a 256 color display 
requires one byte of video memory.  So, to display 640x480x256, you would
need 640*480*1 bytes of video memory.  But 640*480*1 = 307,200.  Since your
vga card does not have 307,200 bytes of video memory, you can't use the 
640x480x256 mode.  If you do the math for 640x400x256, you will find that
it takes just under 256K.  (Note: 1K = 1024 bytes).

Joon Song
joonsong@ocf.berkeley.edu