Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!samsung!olivea!oliveb!amdahl!JUTS!duts!kls30 From: kls30@duts.ccc.amdahl.com (Kent L Shephard) Newsgroups: comp.sys.amiga.advocacy Subject: Re: Blitter vs. 040 (was: Computer Architecture question Message-ID: Date: 16 May 91 19:03:05 GMT References: <1991May15.125954.1993@NCoast.ORG> Sender: netnews@ccc.amdahl.com Reply-To: kls30@DUTS.ccc.amdahl.com (Kent L. Shephard) Organization: Amdahl Corporation, Sunnyvale CA Lines: 64 In article melling@cs.psu.edu (Michael D Mellinger) writes: > >In article <1991May15.125954.1993@NCoast.ORG> davewt@NCoast.ORG (David Wright) writes: > > You just don't seem to understand that: > [ 1 and 2 deleted] > 3) Having two CPUs is ALWAYS faster than just 1, as long as you > pick the jobs that each does correctly > >Not necessarily. Can I pick the 1 CPU? I would think that it depends >on how the system is designed. 1 fast CPU can definitely beat 1 >dedicated CPU and another general purpose CPU. Not to mention the >fact that half of your hardware is being wasted when you aren't doing >graphics. A ray tracer would definitely win with the 1 fast CPU. > >-Mike I agree this ios not the case. If I connect 5 i486 or 5 '040 chips together in a system will that be faster than lets say 1 cpu that runs a 100 mips?? The answer to that is: Depends on the system design. You lose processing power when you add cpu's it is not linear. 20 mip cpu + 20 mip cpu + 20 mip cpu + 20 mip cpu + 20 mip cpu != 100 mips. You lose because of scheduling overhead and you must also realize that you have to have an OS that can do effcient scheduling. Are you going to do static or dynamic scheduling? Symetric or asymetric multiprocessing? Is your cache coherency protocol efficient? How good is I/O performance. Is memory dual ported? Who has priority over data in shared memory? I'll take 1 fast cpu ('040) vs a good one and a dedicated specialized cpu ('030 and blitter). You see unless they can access memory at the same time (dual ported) then one will have to wait for the other eventually. Also the '040 does lots of things in 1-3 cycles (remember it is very fast) so how many cycles will the blitter be able to steal? I'd say not many. Or what happens when the blitter is accessing memory during a cycle steal, how long will it hold the shared memory bus, will the '040 have to wait for it to finish. Smooth animation is possible on the NeXT dont be fooled. Screen updates aren't as slow as some would like you to believe. I recently played around on a NeXTstation color for a while (1-2 hours) the performance is not noticably different from my monochrome machine. Animation is smooth and it is >30fps. One thing you all must remember even the animation on an Amiga or any machine for that matter will slow down when you start running a lot of processes. When the A3000 is runnig Unix how is animation on it? Kent -- /* -The opinions expressed are my own, not my employers. */ /* For I can only express my own opinions. */ /* */ /* Kent L. Shephard : email - kls30@DUTS.ccc.amdahl.com */