From: bloc1469@ee.ee.uwm.edu (Gregory R Block)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: Comdex/Quicktime released for the PC
Date: 5 Jan 1993 20:49:03 GMT
Organization: Electrical Engineering Dept. University of Wisconsin - Milwaukee
NNTP-Posting-Host: 129.89.2.33

In article <1993Jan5.180425.27724@ra.msstate.edu> skip@tacky.cs.olemiss.edu (Skip Sauls) writes:
>I'm going out on a limb here as I'm certainly not a hardware type, but 
>what the heck, this is .advocacy, isn't it?  :-)

I think so.  :)

>The Lisa chip allows for 64bit access to video memory, whereas the older
>Denise chip is 16bit.  The clock remains the same at 7.16MHz, but I've
>heard that some parts of the chips run at 14.32 and 28.64MHz.  Commodore
>claims that the AGA has 4x the bandwidth of previous Amigas, which would
>imply that the A4000 could do 28MB/sec...
>
>Of course, I really don't believe that this is true, but it sounds great,
>doesn't it?  :-)  
>
>It would certainly be nice if a few of the C= engineers would step in and
>set us all straight on these matters.  Any takers?

Will any engineer do?  :)

Okay, here's the story.  Yes, the Lisa fetches 64-bits each access.
It does this by fetching one 32-bit longword, and then fetching the
second in page mode, which is why AGA needs page-mode ram in chip.
The old Denise was 16-bit.  So, the 16->32bit width change is 2x, and
the page-mode access makes it 4x.

HOWEVER.

The bandwidth change is ONLY for the chipset.  Other than that, the
bandwidth for the processor is still 2x that of old amigas, or the
same as the 3000's, due to full 32-bit access of chip ram.  HOWEVER,
one must remember that the contention limitations have gone up a LONG
way.  You will no longer see contention in the places you used to.  As
an example, an ECS mode known as Productivity, at 4 colors, would eat
ALL bandwidth except vblanks due to contention.  There is no longer
any contention in that mode, and you've got the full bandwidth to
chip.  So, all in all, it takes a lot more to make it eat the
contention.

A DBLNTSC 640x400 with 8 bitplanes will bring you back to that, if I
understand correctly, though I'm not sure on this...  I think I might
be off by a power of two on this one, which would mean you'd only have
a 50% contention level rather than 100.  Chris, Mike, or Dave will
hopefully break in on this one.  (shrug)  Or all three, actually.  I
think that they've taken a vacation, because I've not heard from any
of them here or anywhere in a while.

(News flash:  Marc Barrett says that the entire C= R&D dept. was
fired!  ;)

>I wish that I knew.  There are supposed to be animations by Chris Green
>which are 30-60fps full-screen, but I've not seen them myself.  Apple
>seems to be a bit better than Commodore at releasing internal software
>which promotes the machine.  Boing!, Fields, RoboCity, and other demos
>convinced me to buy an A1000, but there is nothing like that which shows
>of the features of the AGA machines, which is a shame.  Oh well...

I agree.  Chris Green should write a couple of demos and release them.
Someone who knows the ins and outs of high-speed graphics in general
would probably make a relatively good demo.  :D

He can show us that real-time texture mapping he mentioned...

Greg
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