I believe this short explanation has made it somewhat clearer to you now what hides behind PAT technology in reality. This way, ASUS’ trick with enabling PAT in its ASUS P4P800 is of no mystery any more. When 800MHz bus is activated, the mainboard sets the FSB frequency to 200MHz, but doesn’t report it to the chipset, as Intel’s reference design requires. As a result, the chipset thinks that the bus frequency is still 533MHz, and hence the memory is addressed in a shorter and faster way without any additional buffers. As you see, everything is as simple as ABC. This is exactly the reason why other mainboard manufacturers started using “fast mode” for work with the memory subsystem for the bus frequency of 800MHz and speeded up their i865PE based solutions up to i875P based ones.

But let’s return to ASUS P4P800. When we tested the performance of this mainboard with enabled HyperPath mode, we discovered a pretty weird phenomenon, which didn’t correspond to any company’s claims. Namely, ASUS suggests that you should set Memory Acceleration Mode in BIOS Setup (Advanced/Chipset section) to Enabled, if you want to really feel the advantages of HyperPath technology. However, our experiments showed that this option hardly tells on the performance. But there is another parameter in BIOS Setup, which is responsible for the use of faster memory access mode. It is Performance Mode available on BIOS Setup Advanced/JumperFree Configuration page. This parameter does affect the performance a lot. Note that the lowest performance will be achieved if you set it to Auto mode, and by setting it to Standard or Turbo you will get about the same results.

To get a better idea how greatly this option influences the performance, we tested the memory performance at different settings. The tests were run for 200MHz FSB and dual-channel DDR400 SDRAM working with 2-2-2-5 timings. We ran SiSoft Sandra 2003 Memory Benchmark:

As we see, the highest memory performance is achieved when we set Memory Acceleration Mode to Auto and Performance Mode – to Turbo. Here we should also point out that with Performance Mode=Auto the memory subsystem performance drops down significantly (maybe the “optimized” algorithm is disabled in this case) and only in this case Memory Acceleration Mode can really affect the system speed. To prove this conclusion we ran the Checkpoint demo from Return to Castle Wolfenstein game (1024x768x32) with different settings and tried to see how they tell on the fps rate. For our tests we used Pentium 4 3.0GHz and ATI RADEON 9700 Pro graphics card:

Again the results are the same: the highest performance is achieved with Performance Mode=Turbo and Memory Acceleration Mode=Auto. These are the settings we would strongly recommend to ASUS P4P800 with. The instruction to enable the HyperPath technology by setting Memory Acceleration Mode=Enabled is completely wrong. So, it is not only Intel that misleads the users. As we see, ASUS is also not that sinless.