With this memory we could increase our CPU external bus (FSB) up to 295 MHz with stability, making the memory modules to run at 1,180 MHz, a 10.69% increase over Patriots’s labeled spec. We could configure our FSB even higher, but the system was unstable. We considered our system stable when we could run PCMark05 and Quake 4 at least four times without crashing.

With the competing product from Corsair, TWIN2X1024-8500, we could set our FSB only up to 279 MHz, making the memory to run at 1,116 MHz.

Since we have an unlocked CPU, we decreased the CPU multiplier from x11 to x10 to make our CPU running at a lower internal clock rate, checking if what was preventing us from pushing the memories even more was the CPU, which could have already reached its overclocking limits. However, the results were just the same, so what was limiting our overclocking was really the memory kit being used.

With this overclocking set, we achieved 122.07 frames per second on Quake 4, a 10.62% increase. Keep in mind, however, that this improvement also reflects the increase on our CPU internal clock rate, since the CPU clock was increased from 2.93 GHz to 3.25 GHz.

The screenshot below was taken with CPU-Z. This program shows the real clock rate for both memory and CPU. Our CPU works externally at 266 MHz transferring four data per clock cycle, thus the labeled 1,066 MHz external clock rate. DDR2-1066 memories work at 533 MHz transferring two data per clock cycle, thus the labeled 1,066 MHz clock rate. On our overclocking, the CPU was running externally at 295 MHz and the memories were actually running at 590 MHz.

Figure 5: Patriot PDC21G8500ELK modules overclocked.