Memory performance
Our synthetic memory tests should enlighten us about the effects of Prescott's larger caches and improved prefetch mechanisms, so we'll kick things off with them, as usual.

Better prefetching seems to give the Pentium 4 'E' chips—that is, the Prescotts—a slight edge over the Northwoods in Sandra's bandwidth test, which is already very aggressive about using buffering and the like to achieve the fastest possible results. The Athlon 64 FX-51, with its built-in dual-channel memory controller, still leads the pack in Sandra.

Cachemem's bandwidth test is less aggressive, and Prescott's improved prefetch algorithm appears to make a much bigger difference here. The Pentium 4 'E' chips romp in this test.

Linpack shows us just what we might expect from Prescott's larger L2 cache. You can see how the Northwood's performance drops off around about 512K, but Prescott continues unabated into larger matrix sizes. Prescott also performs very well on the far right side of the graph, when we're well into main memory. Again, better hardware prefetch is the likely reason for this improvement.

However, the real shocker here, at least for me, is the Prescott's relatively low peak throughput in terms of MFLOPS. The Prescott peaks well below the Northwood at the same clock speed. That's likely due to lower floating-point math performance produced by Prescott's longer pipeline.

One other thing to note: the crazy insane light blue line towering above all the rest is the Pentium 4 Extreme Edition 3.4GHz. That puppy, with 2MB L3 cache, just abuses our Linpack test. Just thought I should mention that.

Prescott demonstrates slightly higher memory access latencies, which might be the result of its slightly higher L2 cache latencies. Northwood chips are generally a few ticks faster than the Prescott at our chosen sample size. Prescott's improved prefetch seems to mask this latency in our bandwidth tests, though.

And, of course, the Athlon 64 chips with their built-in memory controllers are easily quickest overall here.