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Matching CPU with FSB and RAM Clock Speed?

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February 8, 2009 10:55:02 AM

Ok so I was just reading an article on these forums about match your CPU's FSB to you mobo FSB and your memory clock speed. So I'm looking at getting a Intel Core 2 Quad, the FSB is 1333, I think I'm looking at doing DDR2 Ram unless its a better choice to go with DDR3. But I have been looking into DDR 800 and 1066 (8 gigs) and DDR3 1333 (6 gigs), what do you think my best option is, I understand that the price on ddr3 is a good deal higher and sacrificing latency (so it pretty much runs about the same speed as far as noticable difference). But in the factor of matching my FSB niether of the DDR2 would work correctly to full potential, right? I was also reading if you go with have the FSB speed meaning DDR2 667. Would that work better than the 800 and 1066?

Also just a side question, as far as dual channel and triple channel. If I were to put 8gb of DDR2 into the 4 slots, is it still running dual channel or not? Is there more benefits to having 8gb non-dual channel vs. 4gb dual channel? What does dual and triple channel actually do for me. Sorry lots of little question, just building a new system and don't wanna buy excessive parts if its not really needed. This computer will be used for gaming for sure BTW. Thanks to all that help in my search in advance.
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February 8, 2009 11:26:36 AM

for a cpu fsb of 1333 you'll only need DDR2 667 for 1:1 ratio, but if you plan to overclock via FSB then DDR2 800 and 1066 will allow you to do that without overclocking the memory in the process as well. (though I have DDR2 675 running at 900 with fsb of 450, so you _can_ oc the memory if needed). and if you run the 800 at the stock 667, you can tighten the timings a little without losing stability, so it would still be running at full potential, so to speak.

8 gigs DDR2 in 4 slots will run at dual channel, triple channel is only for X58 mobos and nehalems (core i7) with DDR3. triple channel uses 3 (or 6) ram modules in parallel instead of 2 or 4 in dual channel, increasing the memory bandwidht and thus the read/write speeds as well. Whether there is any real world performance increase depends higly on the application used, most apps aren't memory bandwidht starved at dual channel at the moment and wont really benefit from triple channel. If the modules are mismatched in size (per channel) it wont use dual channel but single channel mode instead, this will have negative effect on most apps/games performance, far greater than the dual-to-tripple increase would be...
February 8, 2009 11:39:38 AM

Kari said:
for a cpu fsb of 1333 you'll only need DDR2 667 for 1:1 ratio, but if you plan to overclock via FSB then DDR2 800 and 1066 will allow you to do that without overclocking the memory in the process as well. (though I have DDR2 675 running at 900 with fsb of 450, so you _can_ oc the memory if needed). and if you run the 800 at the stock 667, you can tighten the timings a little without losing stability, so it would still be running at full potential, so to speak.


So if I were to do ddr2 800 or 1066 I would have to over clock my FSB to 1600 or 2133. Probably the 800 would be the better choice there right? Would that increase my CPU overall Ghz? I've never really looked into overclocking but as long as I'm not doing anything to crazy where I'll will need water cooling or some crazy system that I have to keep a ton a maintience on I'll be fine.
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February 8, 2009 12:10:17 PM

1. not necessarily, you can run it at some 'uneven' lower speed as well, like 750 or 900 respectivily, depending on the fsb oc, 2. technically yes since 1066 is pretty much factory overclocked 800, 3. yes if you dont lower the cpu multiplier.

and just to make sure, that cpu fsb is 'quadpumped' so 1333 has base fsb of 333, memory is ''dualpumped'' so base 333 uses 667 ram (with 1:1 ratio, this ratio can be changed as well but Core architecture doesn't really get any benefits from running memory faster out-of-synch). The final cpu speed is determined by the cpu multiplier times base fsb, ie 333*8=2.6GHz if the fsb is increased to 400*8=3.2GHz etc... I have E6550 with multi of 7 and fsb 450 so it is running at 3.15GHz. the highest available multi depends on the cpu model, lowest is allways 6. Only on extreme models can you increase the multi beyond the stock value. So basically it all comes down to the desired final OC and the FSB needed to get so far with the chosen cpu.
IF it takes fbs greater than say 450 then the 1066 could be better choice, but imho most 800 should be able cope with that as well. Some mobos might have problems with very high fsbs as well but most G/P35/45 should run close to 500 if properly pushed, though your mileage might vary :D 

edit and you'll need good aftermarket cooler to oc, like thermalright ultra 120 extreme, TRUE for short. check some reviews at anandtech or xbitlabs
February 8, 2009 4:21:36 PM

I did understand that completely. So how about this, I am going to have a Intel Core 2 Quad Q9550 Yorkfield 2.83GHz 1333mhz FSB. My motherboard will be either one of these here,
780i
or
780i
or for DDR3 ram 790i

What would be my best option for ram for any of these mobos?

Also would a mobo that says its ddr3 be backward compatible?
February 8, 2009 6:34:29 PM

More than not, just grab DDR2 800 and you'll be fine.

A 2x2Gb set is best, unless you want 8Gb, then just get 2 2x2Gb sets.

You're worrying too much about it, actually. If you only run your FSB and processor at 333 (1333), RAM will downclock to 667Mhz, and that's fine. More than not on Core 2's, memory speed doesn't have a big impact.
February 8, 2009 6:42:22 PM

DDR3 is not compatible with DDR2,

if u have the q9550, then the best RAM is DDR2 800, as this will allow u to up the CPU fsb up to 400 (1600fsb) without much of an issue.

this will then require the multiplier of the CPU to be dropped to 7 to give u the 2.8Ghz (almost 2.83Ghz stock).

then if u decide to overclock the CPU, u just up the Multiplier by increments of 0.5 or 1 (7.5,8,8.5,9) and so on.

dont forget that the CPU will require more V-core the higher the CPU is overclocked.

as suggested, the Thermalright ultra 120 extreme is a very efficient cooler combined with 2 quiet 120mm fans.

depending on ur taste, but if ur an nidia fan (or have an Nvidia GPU) then the Nvidia mobo's are perfect if ur going to sli, but if ur looking at ATI GPU's or just single GPU setup then the Intel mobo's will better suit u.

the intel mobo's are more efficient on the overclockin side, and do run cooler.

if u decide to go with the intel chipset, then i would recommend the Intel P5Q-pro P45 chipset, as it is great overclocker, at a price that is alot cheaper than the equivilant Nvidia chipsets.

hope this helps.
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