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From: melling@cs.psu.edu (Michael D Mellinger)
Subject: Re: Blitter vs. 040 (was: Computer Architecture question
In-Reply-To: mykes@amiga0.SF-Bay.ORG's message of 14 May 91 00: 18:48 GMT
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	<a29H2#n2@cs.psu.edu> <mykes.2568@amiga0.SF-Bay.ORG>
Date: Tue, 14 May 1991 06:22:07 GMT
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In article <mykes.2568@amiga0.SF-Bay.ORG> mykes@amiga0.SF-Bay.ORG (Mike Schwartz) writes:

   Again, if you use the 040 to do graphics instead of a blitter, you lose the ability
   to do things in PARALLEL with the CPU.  The 040 has a limited number of Cycles (yes
   gobs of them), and using them for rendering ovbiously gives you less of them for
   doing what work your applications do (or your multitasking OS...).

What am I missing here?  You have 15 mips in 1 second or you get 12
mips the 030 + blitter.  Does it really matter if they are running in
parallel as long as the bus isn't limiting you?

   The custom chips in the Amiga can and often do cause the CPU to wait when it
   accessis CHIP RAM.  If the blitter is running in NASTY mode, for example, it will
   steal every possible cycle from the CPU (on the CHIP BUS only).  If you are using
   some of the higher resolution graphics modes (like 640x400x16 colors), the display
   hardware steals 100% of the CPU (and blitter) cycles except for horizontal and
   vertical retrace.  The Amiga workbench is 640x200/400 x 2 planes, because it
   steals no cycles in this mode.

So, the blitter is stealing from the faster chip, the 68030?

   Your question about graphics modes shows that you haven't learned much at all
   about the Amiga (RTFM, please).  To get 640x400x4096 colors, you can use a single
   bitplane of 32,000 bytes, but your graphics mode is seriously limited (you have to
   do EVERYTHING with the copper).  In HAM mode, you can't go 680 horizontal, but you
   can open 10 (96K each) 4096 (6 plane) 320x400 screens in 1Meg of CHIP RAM.  The Amiga
   does support overscan, so you can get hirhger resolutions (I'm using 704x484).

Yeah, the Amiga has a dozen different graphics modes.  That's nice.
It will probably have a dozen more before the Amiga dies.  In the mean
time, the blitter is on its way to becoming the bottleneck in the
system, if it already hasn't.

   The Amiga 500 doesn't even ship with 1Meg of RAM (the 500P does), and it is fully
   able to run the entire Amiga OS (multitasking and all), and virtually all applications
   for the Amiga (except the very few that require 1+ memory).

Yes, so what!  Are we bragging about how few paper clips we wasted?
Memory is cheap.  We just bought 16MB of memory for $650 for our NeXT.
Functionality is more important.  On the NeXT we have an OS that
supports 24 bit color, has memory protection, virtual memory, and does
much more.

-Mike

