Intel Pentium 4 1.4GHz & 1.5GHzby Anand Lal Shimpi on November 20, 2000 12:54 AM EST
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With a 50% higher clock speed over the rest of the processors compared in the above chart, we get to see some interesting aspects of the Pentium 4's performance. For starters, while the clock speed advantage should have given the Pentium 4 an incredible lead at the start, we can see that it peaks at the same performance level as a 1GHz Athlon which was one reason for choosing only 1GHz processors to compare here.
Because of the Athlon's larger L1 Data Cache (64KB vs 8KB on the Pentium 4), the Athlon reaches its peak performance much quicker than the Pentium 4 does. The two difference architectures yield two different performance curves obviously, and depending on the size of the data set the Athlon in some cases is faster than the Pentium 4, and in other cases the Pentium 4 is faster. Judging by these performance graphs it wouldn't be surprising to see an Athlon at 1.5GHz offer an even greater level of performance than the Pentium 4 considering that the 1GHz Athlon is coming very close to doing so already.
What is interesting is what happens after the L1 and L2 caches are filled and the data set begins to grow in size. The latter part of the graph is as close to clock speed independent as possible since its mainly depending on memory and FSB performance. In spite of using the same memory controller as the i840 chipset, the Pentium 4 on the i850 chipset holds a 75% performance advantage over even the fastest AMD 760 DDR platform.
There are a number of explanations for this. It could be that the Pentium 4 truly requires RDRAM to shine, it could be that the Pentium 4's 400MHz bus is giving it a major performance advantage here among other possibilities. Since the i850 shares the same memory controller as the i840 it is unlikely that RDRAM is the cause of that performance curve, in which case the 400MHz FSB could really be coming in handy as it is able to give the Pentium 4 the bandwidth it needs. However it is hard to believe that the AMD 760's 266MHz bus isn't enough to do at least the same.
The only remaining explanation points us in the direction of the Pentium 4's architecture itself. As you're sure to see in benchmarks floating around, the Pentium 4 will do quite well in SPECfp_2000, partially because of processor specific compiler optimizations that show you exactly how much performance is to be gained from taking full advantage of the Pentium 4's architecture, but also because with some of the large data sets of the benchmark, the Pentium 4's highly advanced branch predictor unit can come in handy. By correctly predicting a large portion of branches, the Pentium 4 should be able to excel at most of the SPECfp_2000 tests which we determined to have large data sets. This Linpack performance curve is indicative of something quite similar happening here, as the data set increases in size the Athlon and the Pentium III drop down to a lower level of performance while the Pentium 4, with a more advanced branch predictor rises to the top.
Looking towards the future the Pentium 4's performance curve here could be something to keep in mind, but let's take a look at its performance in today's applications before concluding on that.