Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!sri-spam!sri-unix!ctnews!pyramid!decwrl!labrea!rocky!ali
From: ali@rocky.UUCP
Newsgroups: comp.sys.mac
Subject: Re: Bit Blitters
Message-ID: <173@rocky.STANFORD.EDU>
Date: Tue, 10-Mar-87 13:22:22 EST
Article-I.D.: rocky.173
Posted: Tue Mar 10 13:22:22 1987
Date-Received: Wed, 11-Mar-87 22:03:46 EST
References: <43140@beno.seismo.CSS.GOV> <172@rocky.STANFORD.EDU>
Reply-To: ali@rocky.UUCP (Ali Ozer)
Organization: Stanford University Computer Science Department
Lines: 34

In article <43140@beno.seismo.CSS.GOV> mo@seismo.CSS.GOV (Mike O'Dell) writes:
>The only problem with bit blitters is that none of 
>the chips available actually do what you want in
>all the cases.   ... A vanilla 68K
>can blit faster than any currently known hardware
>chip.

One more important point about blitters. A blitter is essentially another
processor, except it can do various things better than a CPU 
(for example, area fills, moves, boolean operations on bit planes,
etc). But obviously there are some things it can't do (such as multiply,
divide, various complicated addressing modes, etc). Thus a blitter and
a CPU live together real well: They are good at different tasks, and, with
a properly designed system (hardware and software), they should each
work on the things they are good at without bothering the other. 

Thus you can expect a performance boost out of your machine even if you
attach a wimpy blitter (ie, a blitter not better (in terms of speed at
which it can move/fill memory, etc) than your CPU). Otherwise, you have a
wonderful $7000 (you need a keyboard and a monitor, no?) system
with a 68020 who spends most of its life redrawing windows. On the
Amiga, while the 68000 is working on a CPU intensive program (such as
compiling, TeXing, etc), I can go ahead and move windows around, resize them,
click and view menu items, etc, without interrupting the computations.
This is because the blitter is responsible for doing most of the 
windowing stuff, and except for the few clock cycles the 68000 spends
on instructing the blitter what to do, it can go ahead with what it was
doing.

Sorry for laboring the point, but blitters are far more important and
capable than you seem to think they are. And they are a necessity in
any system destined for graphics work.

Ali Ozer, ali@rocky.stanford.edu