place said:
Ok, I saw that ocz just announced their ddr3-1800 modules. My question is at what point does the system stop taking advantage of these high memory speed? I want to buy some ddr3 in the future but I don't want to pay for more speed if my system cannot take advantage of it or if there is no real world applications performance advantage - right now im using a p35 intel chipset.
Are you supposed to buy memory based on what your rated fsb is going to be? How do you guys go about figuring out how much memory speed you need, what numbers do you look at to determine this?
thanks
Intel CPUs operate best on fsb:ram = 1:1. You set your CPU multiplier as high as it will go and then slowly raise the FSB and voltages until it won't OC any more. That point is pretty much known for most CPUs. High and unlocked multipilers are expensive chips because they usually overclock higher.
For example, the Q6600 has a multiplier = 9x and a default fsb = 266 for a default speed of 9 x 266 = 2.4 ghz and (266 x 16 = pc4200 the default memory speed).
It is also now known that the Q6600 OCs to about 3 ghz on air, and 3.2 to 3.6on water. Calculating backwards thats 3ghz/9 = .333, so on air your maximum fsb = 333 mhz. Memory is 16x this so that's pc5300. Most ppl buy pc6400 just to be on the safe side, but in fact pc5300 will work perfectly for a large majority of over clockers. That is how you calculate at what point memory is too fast to bother buying for your CPU.
Some people buy higher speed memory like pc8000 or pc8500. They do this often because they think lowering the multiplier and increasing the fsb beyond 333 mhz will make their system faster. But experiment has shown that higher fsb settings result in a 1-3% increase in speed which is hardly worth the cost of expensive memory and mobos.
Alternative, ppl buy this high speed memory because pc8500 operating at pc5300 allows favorable changes in the latency settings. For example pc8500 5-5-5-15 might operate properly at 3-3-3-9 if the memory is set for pc5300. Lower latency allows the system to wait less time for the memory to become stable before the next read or write. Unfortunately, it has also been shown that with the latest chips from Intel of the core 2 variety, this lower latency gives only a few percenage points advantage as well.
So in summary:
1. pick a processor, determine a reasonable possible overclocking based on other's experiences.
2. pick memory based on the overclocking FSB to make 1:1 (with the multiplier as high as possible).
3. pick a mobo that can handle the chip and memory, it doesn't have to be too high end unless you pick a high end CPU.
4. build and enjoy!
5. oh ya, get water cooling if you pick a hot chip (Swiftech h20-220 is nice)
6. don't buy for the future, buy for today, because when the future gets here, everything will be better, cheaper and more fun to build all over again.
