Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!ames!amdahl!netcom!mcmahan From: mcmahan@netcom.UUCP (Dave Mc Mahan) Newsgroups: comp.sys.amiga Subject: Re: General question about relative speeds of A2000 and A3000. Message-ID: <11908@netcom.UUCP> Date: 11 Jul 90 02:54:56 GMT References: <1077@orange9.qtp.ufl.edu> Distribution: na Organization: Dave McMahan @ NetCom Services Lines: 76 In a previous article, sutherla@qtp.ufl.edu (Scott Sutherland) writes: > I just got my A3000 last week. It is VERY FAST and I am >very pleased with it. I had been looking to upgrade my 2000 with >the A2620 or A2630 before the 3000 was announced since I was (and >still am) interested in doing faster ray tracing. I read the >articles in Amiga World and other magazines (also the latest Amazing >Computing). The results show that typical speed increases for the >various accelerator boards are from 5-10 times w.r.t. a vanilla 2000. >Now, this is QUITE respectible, but I was wondering why the speed >increase isn't even greater, especially for math intensive programs >like Turbo Silver and SA 3D/4D. > >The 68000 runs at 7.14 MHz and the 68030 (A3000) runs at 25 MHz. >This is a factor of 3.5 faster. The 68000 is 16-bit and the 68030 >is 32-bit. This is a factor of 2 faster. Thus, even without a math >processor, IN THEORY, the A3000 should be 7 times faster than the >A2000. Now, when I purchased an AT&T PC6300 in 1985, I got an 8 MHz >8087 with it. I was told and had read that the speed increases for >math intensive programs with this chip would be from 10 to 50 times. >Thus, math intensive programs, >ESPECIALLY RAY-TRACING PROGRAMS, should, IN THEORY, run 10-50 times >faster with the math chip than without. So, IN TOTAL, with the >processor being 7 times faster and the math chip being 10-50 >times faster, RAY TRACING programs should run between 70 and >350 times faster on an A3000 than on an A2000, ASSUMING THAT >THE CPU AND MATH PROCESSOR SPEED INCREASES OVER THE 2000 ARE >MULTIPLICATIVE. Even if they are not, then a 10-50 times increase >(should be on the higher end, say 25-50 times) in speed of >ray tracing programs should be realized. > > So I ask you, why are these math intensive programs only showing >a 5-10 times speed increase on a 3000 (or 2630, CSA, Hurricane, etc.) over >a stock A2000? Please let me reiterate that this is NOT a complaint of >the speed of accelerated Amigas, but a point of naive curiosity. You forgot to mention the instruction and data caches that exist on the 68030 and not the 68000, but your point is well taken. First of all, we should assume that the ray-tracer programs you are using are written to make use of the math processor. If they are not, you are out of luck until a new version comes out. I would think that the programs would be supplied with two versions, one for math processor equipped computers and one that works on vanilla computers. If the benchmarks were run without the math processor being used, all you would see are the increases mentioned. If I was you, I'd do my own benchmarks (since you already have the hardware and software) and not rely on the magazine. They may have decided to run just the slow version to see what kind of raw thru-put increases are available from the processor, or they may not have known how to run with the math coprocessor. Now, just because a machine has a 32 bit bus, it doesn't mean that the code needs to access data 32 bits at a time. If the program is written to test one bit of a byte, having anything bigger than 8 bits on the data bus is not going to help. If the program uses 16 bit integers in lots of places, having a wider data bus isn't going to help. I don't know what the programs you mention are using, but I wouldn't just assume that a data bus twice as wide will give you twice as much speed. If the program is written to access a limited resource (like chip memory) quite often, and that resource has to be shared with another thing (like chip RAM does when you have the resolution cranked up) the 030 must wait for other thing to give up access to the resource before it can continue. This effect is observable on the A2000 also, but I would think that the A3000 would be more pronounced. I'm not sure, but I also wonder if the 030 may have to wait a little anyway to access chip memory on the A3000. Someone else (like Dave Haynie at C=) would know better if this is true. There are many other examples of what can slow down a CPU, but I think you get the idea that some numbers just don't multiply linearly when trying to figure CPU speed increases. >Scott Sutherland -dave