Testbed and Methods
We compared the performance of our systems equipped with different amount of RAM following a very simple pattern. We assembled a system with AMD Athlon 64 FX-60 processors and Nvidia GeForce 7800 GT graphics card. Then we installed either two memory modules 512MB each or two memory modules 1024MB each. The memory worked at 400MHz in both cases with 1T Command Rate setting. All other timing settings were also identical to ensure that the performance comparison would be correct and fair.
I have to point out that it is impossible to have the memory timings work at the most aggressive (and best from the performance prospective) settings of 2-2-2-10, even if we have the best DDR400 SDRAM 1024MB memory modules at our disposal. With aggressive timings like that all these memory modules would work unstably. This is exactly the reason why we had to work with the timings set to 2-3-2-10.
Besides the side-by-side performance comparison of the 512MB and 1024MB memory modules, we decided to measure the performance of our test platform working with four 512MB DDR400 SDRAM DIMMs installed. However, I have to stress right away this is not the most optimal configuration for the memory subsystem. The thing is that having four double-sided DIMM modules in an Athlon 64 based platform requires the use of 2T Command Rate setting, which has a negative effect on the performance in this case.
Moreover, there is one more disadvantage of having four DIMM modules in your system, which is indirectly related to the topic of our today’s discussion. The use of four memory modules in Athlon 64 platforms reduces significantly the overclocking potential of the platform by limiting the bus frequency increase. For example, a lot of Socket 939 mainboards refuse to raise the clock generator frequency over 240-250MHz when they are equipped with a full set of four memory DIMMs. By simply removing a pair of DIMMs from the system you can immediately raise the stability bar beyond 300MHz.
Here is a list of hardware components we used to assemble our test platforms:
- CPU: AMD Athlon 64 FX-60;
- Mainboard: DFI LANParty UT NF4 Ultra-D (NVIDIA nForce4 Ultra);
- 2048MB DDR400 SDRAM (Corsair CMX1024-3500LLPRO, 2 x 1024 MB, 2-3-2-10);
- 2048MB DDR400 SDRAM (Corsair CMX512-3200XLPRO, 4 x 512 MB, 2-3-2-10);
- 1024MB DDR400 SDRAM (Corsair CMX512-3200XLPRO, 2 x 512 MB, 2-3-2-10);
- Graphics card: NVIDIA GeForce 7800 GT 256MB (PCI-E x16);
- HDD: Maxtor MaXLine III 250GB (SATA150);
- OS: Windows XP SP2.