Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!well!farren From: farren@well.sf.ca.us (Mike Farren) Newsgroups: comp.sys.amiga.advocacy Subject: Re: Blitter vs. 040 (was: Computer Architecture question Message-ID: <24740@well.sf.ca.us> Date: 12 May 91 20:30:30 GMT References: <3310.tnews@templar.actrix.gen.nz><1991May9.070349.15151@neon.Stanford.EDU><3496.tnews@templar.actrix.gen.nz> <3602.tnews@templar.actrix.gen.nz> Lines: 63 melling@cs.psu.edu (Michael D Mellinger) writes: > As kdarling points out quite often, things are _already_ done > faster if the CPU is used instead. It depends on the kind of > animation involved, and for the delta animations (or whatever they > are called) the Blitter is next to useless. For some block and line > operations too, the Blitter is not useless, but it is slower. > Depending on the CPU one happens to have. >Let's say the 030. An 040 should be > than the 68000 + blitter. No? Not necessarily. There are other limitations. Memory bandwidth is the biggest one - if you have one processor, you are absolutely limited by the memory bandwidth for ALL operations, whereas if you have two, even though they might individually be less than half the speed of the faster single processor, they can multiplex their memory accesses - just like the Amiga blitter already does. What is better, a 68040 trying to run two separate tasks at 25MHz, or a 68000 plus a blitter both driving the memory full out? Answer - probably the 68040, but you cannot guarantee that. It depends on the design of the whole system. >How much does coprocessing matter. Let's say that you can get 10 mips >b/w the two of them. A 15 mip 68040 is still going to give you more >horsepower(33% more). Again, NOT necessarily. A MIP rating of the individual processor presumes that it has full access to all resources, and commonly is not a real-world measure of a system as it actually manifests in the real world, complete with limited memory speed, and, as you say, context switching and other overhead. >How well does the A3000 do animation in its million pixel display mode? A bit of a quandry, here, as the A3000 does not currently have a common megapixel display mode. However, if the Mpixel display is designed correctly, the animation should be no slower than animation at 320X200, provided, of course, that you're only changing the same number of pixels from frame to frame. In fact, I would expect a newly-designed Mpixel display to actually go faster, as the lessons learned in designing the Amiga custom chips are applied, and the slow CHIP memory speed is gotten around. (A lesson, BTW, which IBM seems to have learned, except that they are about two generations behind :-) >Yes, but if in the next generation machine the power of the CPU is >greater than the cumulative power of all the chips in the older >machine then you could throw out all of the old chips and replace them >by the one chip and get a computer that is just as fast(of course >keeping all the chips plus the new CPU would make it even faster). If this were so, then the only technical challenge to EEs would be to make chips as fast as possible, and all the computers we use would be some fancy variant of ECL, running at 500MHz, and requiring Niagara Falls for cooling :-) Seriously - it ain't anywhere NEAR that simple. I've personally designed systems using 8085's (an eight-bit chip) which were comparable in speed to most Intel 286 systems. I've also worked on systems so limited by memory access and I/O speeds that you could have hooked a Cray CPU up to 'em and still gone no faster than an Apple II. -- Mike Farren farren@well.sf.ca.us