First of all, we ran synthetic tests measuring memory subsystem performance. The following table contains the results of Cachemem:
Memory read speed
Memory write speed
Memory copy speed
The shift from the 266MHz to 333MHz bus was evidently advantageous: it proved efficient providing higher memory bandwidth and lower latency. However, we can hardly hope to get similar improvements resulting from the shift to 400MHz bus. The problem lies in the memory subsystem latency. Unfortunately, DDR400 SDRAM doesn’t allow setting such aggressive timings as DDR333 SDRAM. That’s why the latency of a system with 333MHz bus and DDR333 memory is often better than that of a system with 400MHz bus and DDR400 memory. Therefore, the transition of Athlon XP to the 400MHz bus may bring no positive effect at all in some cases. But those tasks that require high memory bandwidth are certainly going to benefit from the faster memory and system buses: the bandwidth of CPU-to-memory highway doesn’t depend on timings much.
Now, the results of SiSoft Sandra 2003:
The numbers are one more proof to what has been said above. The CPU-to-memory bus bandwidth is barely affected by the timings and thus goes up along with increased frequencies of system and memory buses. Meanwhile, the transition from the 266MHz to 333MHz bus brings a 22% boost, while the transition from 333MHz to 400MHz bus – only 17%. This once again tells that the influence of the bus speed onto the system performance will become lower along with the growth of its frequency.
We can say the same things again about the results of PCMark2002.