Manufacturers such as Corsair offer matched pairs of memory modules optimized for dual-channel boards.
The temptation that’s inherent in faster RAM modules is to ratchet up your memory bus clock if you have an older system. For example, you can install DDR400 memory on a motherboard with a VIA KT333 or KT400 chipset for AMD CPUs. While the chipsets don’t officially support the new RAM standard, you can still find tweaking options in the BIOS menus that will raise the clock speed from DDR333 to DDR400 levels.
If the system is unstable with memory clocked at 400 MHz, though, you can forget about fine-tuning the frequency. The memory clock moves in parallel to the front side bus clock and can only be adjusted in large increments, such as from DDR333 to DDR400. The adjustment itself is normally made by fiddling with the ratio to the front-side bus clock ; 3/3 corresponds to DDR333 with the front-side bus at 333 MHz, while 4/3 stands for DDR400 memory clock speeds. For the RAM clock to be increased in smaller intervals, you will have to increase the front-side bus clock in lock-step.
The advantages of stepping up your memory clock in an AMD Athlon XP system, on the other hand, are few and far between. In fact, setting the memory bus to 400 MHz and the front side bus to 333 MHz can even slow down performance. Instead, you’ll get better results from optimizing the timing parameters for the faster memory in BIOS.