SiSoft Sandra Mandelbrot
Next up is SiSoft's Sandra system diagnosis program, which includes a number of different benchmarks. The one of interest to us is the "multimedia" benchmark, intended to show off the benefits of "multimedia" extensions like MMX, SSE, and SSE2. According to SiSoft's FAQ, the benchmark actually does a fractal computation:

This benchmark generates a picture (640x480) of the well-known Mandelbrot fractal, using 255 iterations for each data pixel, in 32 colours. It is a real-life benchmark rather than a synthetic benchmark, designed to show the improvements MMX/Enhanced, 3DNow!/Enhanced, SSE(2) bring to such an algorithm.

The benchmark is multi-threaded for up to 64 CPUs maximum on SMP systems. This works by interlacing, i.e. each thread computes the next column not being worked on by other threads. Sandra creates as many threads as there are CPUs in the system and assignes [sic] each thread to a different CPU.

We're using the 64-bit version of Sandra. The "Integer x16" version of this test uses integer numbers to simulate floating-point math. The floating-point version of the benchmark takes advantage of SSE2 to process up to eight Mandelbrot iterations in parallel.

This test underscores the vector math potential of the Core microarchitecture, which can execute a 128-bit SSE2 operation in a single cycle. The Athlon 64 is completely overmatched here, but as I've said before, the tables may turn when AMD's new microarchitecture arrives later this year with similar vector math capabilities.