The Impact Of the Memory Speed
Finally I wanted to find out if it isn't just the excellent data throughput of Pentium 4's system bus and memory interface that makes it perform so well in Quake 3 and the MPEG4-compression. In ran Pentium 4 twice at 1.6 GHz and 100 MHz system bus, once with the RDRAM clocked at 400 MHz, once clocked at only 300 MHz, reducing its bandwidth from 3,200 MB/s down to 2,400 MB/s. Then I 'overclocked' a 1.4 GHz Pentium 4 to 1.610 GHz by increasing the system bus clock to 115 MHz and thus the Rambus block to 460 MHz, increasing the memory bandwidth to 3,680 MB/s.
You can see that the memory speed does indeed have a major impact on all the benchmark results except of the 3D Studio Max scores. In some cases the difference between the slowest and the fastest score is more than 10%! This proves clearly that Pentium 4 lives from the high memory bandwidth that RDRAM is finally able to deliver. Keep that in mind in case someone wants to sell you PC600 RDRAM!