From: cse_stu@memstvx1.memst.edu
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: Comdex/Quicktime released for the PC
Date: 15 Dec 92 18:28:49 GMT
Organization: Memphis State University

> Of course every pixel in the entire 640 x 480 image is not being updated 
> every frame.  Any animation program which requires you to update the entire
> image on every frame is inefficient at best.
I was talking worst case and it does happen. If you average frame is 25k but
you have two or three frames that are 200k or so then you are going to get a
glitch in the animation. If your Quadra will handle that then I'll believe you
are talking the truth.
> However, note that the Quadra 950 frame buffer is capable of burst (i.e., 
> '040 quadlongword burst cycles) transfer rates of well over 40 MB/sec.  
> Tranferring a 680 x 480 8-bit image in 1/90 of second is a transfer rate 
> of just under 28 MB/sec., which is certainly less than the maximum 
> transfer rate.  (A 640 x 480 screen is 300K bytes, not 256K, by the way.)  
> Of course there are inefficiencies involved.  You've got to get the new 
> image data from someplace (main memory, in this case),  arbitrate for the 
> bus if necessary, allow for VRAM refresh cycles, etc.   So real world 
> transfer rates are quite a bit less than the theoretical maximum.  
> (Although the Q950 frame buffer could sustain a transfer rate of over 40 
> MB/sec. if there were an '040 bus master which could supply the data this 
> fast - say PDS card which did MPEG decompression in hardware, for example.)
> 
The 040 chip can take in 16byte's in fives clock cycles and then it takes at
least five clock cycles to put it back to memeory But the cache does not help
you and the mac bus is lucky if it can push 20mhz to memory and 10mhz to it's
video board. The mac was not designed for speed. You can see this by looking at
an Amiga 3000 running AMax that allows the Amiga to emulate a Mac. The 3000
out runs a mac at the same speed because they have zero wait state memory with
burst mode on and the mac has one or two wait states. I'm not sure because
Apple does not reveal how the hardware works. Another thing is to look at the
editmaster board from DMI for the amiga. This board allows 720 x 486 res. in
video 4:2:2 basicly 21bit video quality(betamax quality) at full frame rate 
for $2500 while on the mac side you have two or three boards that cost $5000 
plus for pic quality less then S-VHS.
> The Quadras will produce NTSC or PAL timing so the video output can easily 
> be sent to videotape.  (You do need an external RGB-to-composite converter 
> to produce color composite video.)  I haven't tried this.  It sounds like 
> an interesting test, though.  I have simply asked the animation program to 
> play back at the maximum rate it can.  The output rate is definitely 3 
> times the rate of a slower Mac whose maximum frame rate is 30 fps using 
> the same software.  Slower Macs scale similarly.
The only board that I have heard that is fast enough for animation is the targa
card which is real expensive and it runs on the bus that is 10mhz.
> Then meet my Quadra 950.  (Maybe you haven't been using the right 
> software?)
> 
> - Dale Adams
Your right seeing is believing.