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PPC vs. Intel: top500 shows Steve wrong

The latest listing of the top five hundred super computers was released in today.

Number five, behind two other PowerPC based machines, an Itanium, and NEC's custom earth simulator, is the MareNostrum machine at the Barcelona Supercomputer Center. It runs Linux on a cluster of 4,800 PPC 970 CPUs running at 2.2Ghz and gets score of 27910 (R/Max =Maximal LINPACK performance achieved (in gigaflops)) and 42144 (R/peak =Theoretical peak performance (in gigaflops)).

Number 14 on the list is Virginia Tech's System X. It has 1,100 dual processor X-servers with the same PPC970 chip used in Barcelona. Virginia's Mac cluster runs at 2.3Ghz and received scores of 12250 and 20240 for R/Max and R/peak respectively.

In Barcelona each PPC contributes 5.8 gigaflops to R/Max and 8.8gigaflops to R/peak. In Virgina, the each PPC contributes 5.6 gigaflops to R/Max and 9.2 gigaflops to R/peak. That peak difference favouring the Mac reflects the slightly higher cycle rate, the lower actual probably reflects factors such as cheaper networking and storage - but I don't know that for sure.

The tenth and eleventh systems, from Cray, use AMD Opterons. Xeon enters the list at number 20: the "Tungsten" system at the NCSA in Urbana-Champaign. That machine has 1,250 dual CPU Dell servers running the Intel Pentium 4 Xeon 3060 MHz with Linux plus another 126 machines handling I/O and storage. Tungsten gets an r/max score of 9,819 and an Rmax of 15,300 or 3.9 and 6.1 per processor.

These numbers lead to an interesting question. Since "everyone knows" that Pentiums are faster and cheaper than powerPC chips, how come they seem capable of only about two thirds as much work even when run at a nearly a third more cycles per second?

Overall, however, the new list is so dominated by PowerPC products and Itanium that long time Intel apologists are now questioning the appropriateness of the benchmark - basically Linpack shows Xeon struggling and these guys therefore want to throw out Linpack.

In fact, however, Linpack is more applicable to the loads that count for Mac users than you might expect. My six year old 300Mhz "Tuxedo" powerbook runs vi just fine, but dies horribly when confronted with a big image transform - exactly the kind the operation Linpack measures.

On the other hand, some of these critics may be right about this being the last or next to last top 500 list - not because Linpack's becoming less applicable, but because IBM's cell (itself powerPC based, of course) could own all the top spots by this time next year.

Paul Murphy wrote and published The Unix Guide to Defenestration. Murphy is a 25-year veteran of the I.T. consulting industry, specialising in Unix and Unix-related management issues.