BIOS and Overclocking
The BIOS of P4P800 series mainboards presented a mystery in itself. The engineers from ASUS developed it practically from scratch, from the basic AMI microcode, to be exact. As a result, the mainboards boasted specific optimizations that would work or not depending on the FSB frequency, memory timings and clock rate, and Setup settings. The situation remained practically the same with the release of the ASUS P4P800-E Deluxe. Its BIOS is like a pea from the same pod to the BIOS of the previous version.
Well, after a scrupulous examination we found some differences: the P4P800-E Deluxe allows configuring the memory subsystem more flexibly. The timings remained the same, though. The appropriate page of the BIOS Setup gives you tools to change DRAM CAS# Latency (2, 2.5 and 3 are the possible values), DRAM Precharge Delay (5, 6, 7 and 8), DRAM RAS# to CAS# Delay, DRAM RAS# Precharge (2, 3, 4), and DRAM Idle Timer and DRAM Refresh Rate.
Besides, there is the option of enabling the Memory Acceleration Mode which seems to be an analog of Intel’s PAT. Then, the BIOS Setup still contains the Performance Mode option that enables some optimizations in certain conditions, which positively affect the performance. However, like with the P4P800, you can only achieve any benefits from setting the Performance Mode option to “Turbo” if 1) the FSB frequency is 200MHz, 2) you use dual-channel memory, and 3) you use memory modules capable of working with 2-2-2-5 timings.
As for the changes I mentioned above, the list of supported memory frequencies for 800MHz-FSB processors has been enlarged. Mainboards of the P4P800 and P4C800 series allowed clocking the memory as DDR266/DDR320/DDR400, while the P4P800-E Deluxe supports DDR266/DDR320/DDR400/DDR500/DDR533 SDRAM!
These additional modes are clearly implemented for overclockers because there are already memory modules available that can work at such frequencies. On the other hand, you should be aware that the bandwidth of the 800MHz processor bus is 6.4GB/s and equals that of the dual-channel DDR400 SDRAM. So the benefits of using DDR500/533 (which has worse timings than DDR400) with 800MHz-FSB processors may look obscure.