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From: dillon@CORY.BERKELEY.EDU.UUCP
Newsgroups: comp.sys.mac
Subject: Re: Blitters again
Message-ID: <8703141159.AA12173@cory.Berkeley.EDU>
Date: Sat, 14-Mar-87 06:59:21 EST
Article-I.D.: cory.8703141159.AA12173
Posted: Sat Mar 14 06:59:21 1987
Date-Received: Sat, 14-Mar-87 19:38:56 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: University of California at Berkeley
Lines: 38

>
>> 	There can be no question that having one or more blitters gives a huge
>> advantage when manipulating displays.
>
>Your're right. Certain operations of moderate complexity - not too simple
>like a memory copy, and not too complex, beyond what it was designed for -
>can be done much more rapidly by a blitter than by a processor like the
>68020. 
>

	Those 'Certain operations' you so glibly discard with a wave of your
Overview comprise about 60% of all video operations.  If you include blitter
aided text display, the figure is around 95%.  Although the 'processor
offloading' aspect doesn't apply as much to the Mac due to it's lack of 
multi-tasking, you still get a pretty hefty gain in speed.  And when your
talking about 8 bit planes for the Mac II, and super-large windows, a blitter
makes all the difference in the world.

>The real question is whether the blitter is worth its cost. Machines like
>the Mac and the Amiga don't run at the limits of speed for the 68000 family.
>Would you rather have a blitter, or have the processor run 30% faster for
>all operations? The cost may be comparable.
>
>And don't say you'd like both. :-)
>
>     Radford Neal

	This may be true in some systems, but as far as the Amiga goes, both
its processor and its blitter can run at full speed simultaniously, and
video refresh doesn't slow down the processor until you get beyond 4 planes
320x(200/400) or 2 planes 640x(200/400).

	As for the Mac II, since the video cards have their own video memory,
it would be very easy for a third party developer to stick on a blitter with
relatively little interference with the processor.  The *real* question is:
"Would QuickDraw Support hardware aided operations???"

					-Matt