From: skip@tacky.cs.olemiss.edu (Skip Sauls)
Subject: Re: Comdex/Quicktime released for the PC
Organization: University of Mississippi, Dept. of Computer Science
Date: Tue, 5 Jan 1993 23:46:23 GMT

In article <1ics7vINNqcf@uwm.edu> bloc1469@ee.ee.uwm.edu (Gregory R Block) writes:
>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.  :)

I had to check because sometimes .advocacy articles get cross-posted to
.misc and some bozo sends me an automatic letter whining about it.

>>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?  :)

Sure, I'm just relieved that I'm not getting flamed to a crisp for my
answer.  :-)

>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.

I see, that is a better explanation than most others.

>HOWEVER.

Uh-oh.

>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.

This jives pretty well with my experience.  Productivity 4 color on the
A3000 is fairly slow, but the A4000 doesn't slow down much until you hit
256 colors, and even then it is faster than the A3000...

>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.

The 256 color modes are about as snappy as a fast SVGA card on a 486,
with the Amiga winning for scrolling, the Clone on smooth redraws.  It
is not unbearable to use, but I find myself sticking with 64 colors as
a nice speed/color compromise.

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

Nah, they're on a road-trip to Iowa to kill the bastard...  :-)

>>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

Maybe we should flood his mailbox with requests.

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

Heck, didn't he work on Ultima Underworld or something like that?  A little
demo along those lines would be nice.  :-)

>Greg
>--
>(: (: (: (: Have you overdosed on smileys today?  Why NOT!?! :) :) :) :)
>(: "Our father, who art in Iowa, Hollow be thy head, Thy ideas run    :)
>(:  Thy will be done, At Commodore as it is at Apple"  -Dan Barrett   :)
>(: (: (: (: (: (: (: (: (: (: (: (: () :) :) :) Wubba, the Dark Angel :)

Skip Sauls, Amiga Advocate
skip@tacky.cs.olemiss.edu

Newsgroups: comp.sys.amiga.advocacy