RAM, RAM Ratios, and FSB

[jeanluclariviere]

Hi everyone, New to overclocking, new to the forums. I've been reading more and more about overclocking, and constantly keep finding myself here - I finally managed to get a PC together - so now to my question.I'm running 2 x 1Gb Corsair XMS DDR2 800mhz. From my understanding, they are actually running at a base speed of 400mhz each. Now, if im running a Pentium Dual Core 2.2Ghz proc. at a bus speed of 200mhz with a RAM ration of 1:1 does that mean I can push the proc. another 200mhz before reaching the RAMs rated speed ? I don't think so, and believe i am missing part of the equasion. Any help would be greatly appreciated.Thanks in advance, JL

 

[flyin15sec]

You're correct if you have your ram at 1:1, then your memory would be running at 200mhz(DDR2400mhz)

 

[V3NOM]

Yer, but $5 says the e2180/5200 cant get to 400mhz FSB...

 

[jeanluclariviere]

I dont plan on pushing the board to 400mhz, but for sake of argument, I could infact push the fsb another 200mhz without worrying that the ram would be overclocked, correct ? - And if that is infact the case, and I begin increasing the FSB, and suddenly i get an unstable report, or the blue screen of death (as i've read so often on other forums) I could safely assume that it is the CPU faulting and not the RAM ? Thanks again.

 

[flyin15sec]

You could do 400FSB, but you'll have to lower your CPU muliplier. By default the muliplier on E2180 is 10x, the best option would be an 8x multi.

400FSB * 8 = 3.2ghz OC.

another safe bet is 333 * 9 = 3ghz OC.

The choice is really yours, as you can play with the memory ratio that will put you closest to your rated memory speed.

 

[CompuTronix]

jeanluclariviere,

The following is from a similar thread - http://www.tomshardware.com/forum/247906-29-ratio#t1781779 - posted in July this year, which may help to clarify your thoughts and answer your questions:

Ah, but wait... there's more! Let's consider some of the additional variables involved in the memory big picture:

A ratio of 1:1 provides the best level of stability, since the memory controller, which is an integral part of the northbridge chipset for Intel processors, does not need to translate data flow across the FSB between the memory modules and the processor(s). Also, since memory and processor FSB clocks are synchronous at 1:1, (400:400 or DDR 800), there is no additional latency introduced.

If a minimal ratio of 4:5 (400:500 or DDR 1000) is used, then the resulting increase in memory frequency is effectivey cancelled out by the latency introduced in translation across the FSB between memory and processor clocks, and no increase in memory performance can be noticably detected in benchmarks. Also, asynchronous or mismatched clocks create an element of potential instability within the memory controller, so depending on the chipset, an increase in northbridge and memory voltage is required for stability, which results in more heat, and less FSB overclock ceiling.

If a more aggressive ratio of 2:3 (400:600 or DDR 1200) is used, then the increase in memory frequency can marginally overcome the latency introduced in translation across the FSB between memory and processor clocks, resulting in a marginal increase in memory performance, which typically yields an increase in memory benchmarks of 2 to 3%, and is relatively negligible in terms of overall system performance.

In the case of expensive DDR3, where a ratio of 1:2 (400:800 or DDR 1600) or 2:5 (400:1000 or DDR 2000) is used, even with the tightest timings, an increase in memory benchmarks of only 3 to 4% is yielded over DDR2 800, which once again, is relatively negligible in terms of overall system performance. It's also noteworthy to consider that memory timings of 4-4-4-12 compared to 5-5-5-15, will yield an increase in memory benchmarks of less than 2%. However, for those of us who have the need for speed, we'll take whatever we can tweak.

Additionally, at equal specifications, 4 memory modules offer less FSB overclock ceiling than 2 modules, since more northbridge and memory voltage is required to maintain stability, and 4 slots require twice the current of 2 slots, again resulting in more heat, which typically is pulled into the CPU cooler, where it can increase processor temperatures by a few unwanted degrees.

I hope this helps to provides a greater degree of perspective (no pun intended).

Comp

Incidentally, I run my rig at 1:1.