From: cse_stu@memstvx1.memst.edu
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: Comdex/Quicktime released for the PC
Date: 20 Dec 92 11:32:20 -0600
Distribution: world
Organization: Memphis State University

> The Q950 VRAM does 3/2/2/2 write bursts.  (2/1/1/1 is zero wait state, so 
> this is clearly not that.  OK?)  The initial access time is low because 
> the VRAM is always run in fast page mode.  This is a very definite 
> performance advantage for large data block transfers which tend to 
> sequentially access VRAM.  Yes, sometimes you get page misses - 3/2/2/2 is 
> best case.  This totals to 9 clock cyles per burst, at 30 ns per clock 
> cycle on a 33 MHz machine, with 16 bytes of data moved per burst.  16bytes 
> / (9 * 30 nS) = 59.26 MB/sec.  Practical inefficiencies (VRAM refresh, 
> read transfer cycles, page misses, etc.) reduce this somewhat, but 
> certainly not by the 33% or so it would take to get down to 40 MB/sec.  40 
> MB/sec. is actually a conservative number.
I've seen both the 850 and 900 that run at 25mhz and they are dogs ruinning sys
7.0. I can't believe that a 33mhz would make that much difference. It is a 1/3
increase in cpu speed but the ram and bus are at the same basic speed. The
other point is that for an animation you are moving data from main memory to
video memory and as you said main memory is slower that would seem to give you
less of these high speeds. Push when you are moving raw data from main memory
to video memory your caches don't help you. No util I get the 040 book I cann't
fight you.

>> > Now wait a minute.  Why is the 10 MHz bus fast enough for animation 
>> > now, 
>> > but it wasn't earlier in your post?
>> It is the only card out for the mac that has video quailty.
> 
> I see.  The high video output quality makes it fast.  Hmmm.   So for good 
> animation performance it doesn't matter what speed the board runs at, just 
> what that signal quality of the video output is?  Interesting theory.
My point was that they only video board that gives you video quailty(good) is a
board that runs on the nubus. The targa board is stuck in slow speed. You heard
me wrong when you thought I said it could do fast animation because it can not.
I agree that the direct video is faster then the targa board but unless you
pay $2000 for a scan line converter your output to video from your mac's
internal video is going to look bad compared to other computers like the amiga
that are made for video.
> Standard off-the-shelf stuff, like I mentioned in my first post.  I've got 
> a MacroMind Accelerator animation (the frames of which were generated in 
> Infini-D) which is 4.2 MB and runs on a 640 x 480 8-bit screen.  It has 36 
> frames and plays back at an average frame rate of 77 fps.  Allowing for an 
> initial background screen (300KB), this translates into an average data 
> update of about 116 kB per frame.  At 77 fps this is a data transfer rate 
> of just under 9 MB/sec.  (Note: MacroMind Accelerator does not use the 
> '040's MOVE16 instruction, and so does not do burst cycles to VRAM, only 
> longword transfers.  The data transfer rate could probably be doubled if 
> bursts were used.)  
I remeber when the accelerator software came out. It makes the animations go a
lot faster but when there is a big change on the screen to a new backround or
something you can always see the animation slow down or stop to make the
change. So maybe it does not make a difference to you but I am look for smooth
animations. MacrcoMind comes close if you know what you are doing but you still
it frame flicker because the computer does not know when the video is
displaying a fram. This is the real advantage on the amiga because I can tell
the amiga to wait for a scanline that I want and it will tell me when it is
being displayed. The mac does not have this kind of control. I go example is
the new alpha digital workstations. They have a very high speed bus faster then
the amiga or the mac and it still flickers from time to time while it plays an
animation. So high speed alone does not cut it. You need control. I still don't
see how you are getting that kind of speed because if you could you would be
able to do 640 x 480 x 24 bit at 30 frames per sec. If you are really telling
me the truth send me a video tape of an animation that changes each frame to a
completly different thing like different digitized pics etc. I can provide you
with a mailing adrress to anyone who can get a mac to do full frame rate video
with an animation that is a worst case animation (big changes in every frame).
============
video man
cse_test@memstvx1.memst.edu
Xref: sparky comp.sys.amiga.advocacy:31337 comp.sys.amiga.misc:18555