From: skip@tacky.cs.olemiss.edu (Skip Sauls)
Subject: Re: PC (OS/2) / Amiga debate -- hopefully a rational debate <- (ha!)
Organization: University of Mississippi, Dept. of Computer Science
Date: Fri, 11 Sep 1992 17:35:24 GMT

In article <1992Sep11.165440.13372@sol.ctr.columbia.edu> jerry@connection.prospect.com (Jerry Shekhel) writes:
>copes@cs.curtin.edu.au (Simon Cope) writes:
>>
>>>Yes.  A typical 1MB VGA can store 6 screens of 640x480x4 graphics.  
>>>Switching is instantaneous, via a "display start address" register.
>>
>>Gee hey 6 whole screens.  Must get me one of them.   NOT!
>
>Isn't it true that on the Amiga, the number of graphics screens available
>depends on the amount of Chip RAM installed?  If so, how many 640x480x4
>screens can a typical A500 store?  A3000?

Does the 4 refer to bitplanes or number of colors?  I'll assume bitplanes,
yielding a standard 16 color display.  Given that I have approximately
1.8M free chip mem right now, I should be able to open 11 screens at that
resolution.  The screen I'm typing this on is a single-bitplane 640x200
screen and the Workbench is a 696x480x3 plane screen.  If the Workbench
was 640x480x4 and the screen I'm using were closed, the total number of
screens open could probably be 12 or 13.  Given that I have 2M Chip RAM
versus the VGA's 1M VRAM, this makes sense.

A typical A500 with 512k Chip RAM would be lucky to have 1 screen open
at that resolution, but it might have as many as 3 open if it had any
Fast RAM.

In the real world, both the A3000 and A500 would also use some portion
of the Chip RAM for storing other graphics, the "backing store", the 
sound, and other such things.  I don't know what the practical limit
is for screens, but I've never had a problem with opening several at
a time on my A3000.

>>copes@cs.curtin.edu.au

>+-------------------+-----------------------+--------------------------------+
>| Jerry J. Shekhel  | Molecular Simulations | Time just fades the pages      |
>| Drummers do it... | Inc.  Waltham, MA USA | in my book of memories.        |
>|    ... In rhythm! |     (617) 890-2888    |              -- Guns N' Roses  |
>+-------------------+-----------------------+--------------------------------+
>|           ...! [ princeton mit-eddie bu sunne ] !polygen!jerry             |
>|                            jerry@polygen.com                               |
>+----------------------------------------------------------------------------+
 _____________________________________________________________________________
| Skip Sauls                | |       Head Chief Software Engineer Dude #1    |
| skip@tacky.cs.olemiss.edu | |                    SAIR, Inc.                 |
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