Author: Matthew Hull
Date: 09:30:50 07/11/02
Go up one level in this thread
On July 11, 2002 at 00:18:36, Robert Hyatt wrote: >On July 10, 2002 at 12:53:11, Joshua Lee wrote: > >>On July 09, 2002 at 13:28:54, Robert Hyatt wrote: >> >>>It doesn't... For example, the C90 had a 2 nanosecond clock. The cpu >>>could read two 64 bit words and write one 64 bit word per clock cycle, >>>per cpu. With 16 cpus, that is 16 * 24 * 500000000 bytes per second >>>and that can be _sustained_ forever. >>> >>>Compare that to any PC you want and you see why (a) the supercomputers are >>>so expensive and (b) why the micros have absolutely no chance at catching >>>them in terms of speed. >>> >>192,000,000,000 bytes per second >>That's over 178 Gigabytes a second. Is Bandwidth refered to in this way or how >>fast the memory can communicate with the cpu or both? In Athlon's it's has a 2.1 >>GB/Sec bus it can execute a multiply and add on every clock cycle which gives it >>a peak throughput of 3.2 gigaflops. >> > > >I don't see any way a 2.1 gigabyte per second memory bandwidth can translate >into 3.2 gigaflops. A flop requires accessing two operands, doing something >to them, and putting the result back... IE a flop == 12 bytes of memory >traffic (cache doesn't count because big applications and arrays don't fit >into cache). That translates into maybe 100 gigaflops as a more realistic >number... And I don't believe any PC has a prayer of coming within a factor >of 10 of that number in reality. Right! Even Apple only of only a little more than 1 gigaflop for a 500mhz G4, which has it's own vector processor (ALTIVEC). And this chip flogs any x86 chip as far as FLOPS is concerned. It's the classic memory bottleneck of the micro. Bus speed versus processor speed equals wait states, or something like that.
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