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benefits of memory running synchronous with FSB

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May 26, 2008 10:44:49 PM

So...I'm ready to upgrade my system, and I am pretty sure for the CPU I am going with the new E8400 wolfdale core 2 duo running at 1333mhz fsb. While doing a search on this processor, I encountered a wikipedia article on the core 2 processors, and there was a section on it detailing how core 2 processors receive greater benefit from memory running synchronously with the FSB. For the 1333 mhz FSB of this processor, the ideal memory would be either PC2-5300 or PC3-10600. Now, seeing as I was originally planning on going with PC2-8500 with this system, I don't imagine the difference would be so great, but who knows. So, if I'm going withh a 1333mhz fsb cpu, on a 1333mhz fsb motherboard, should i go ahead and shell out for the 1333mhz fsb RAM? Also, the only 1333mhz RAM is the DDR3 10600 right? There isn't DDR2 at this speed?
May 26, 2008 11:06:19 PM

Ok...I think you might be a little confused about the sync issue.

The E8400 is a processor that has a FSB of 333 and a multiplier of 9 (333 x 9 = 3.0 GHz).

If you were to run the FSB and memory in sync, you'd need DDR2 667 (2 x 333).

If you overclock the processor to 400, then you'd need to run memory that rand at DDR2 800 (pc 6400) - 2 x 400.

Hope that helps you out.

You'd need 667 if you don't plan on overclocking (why not? - it's free and not dangerous if you know what to do) or you can get higher speeds if you plan on overclocking.

May 26, 2008 11:52:48 PM

so i see how you derive the 3.0 Ghz chip speed with that formula, but then why do they say it runs on a 1333Mhz FSB, or 4x333?
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May 27, 2008 1:38:56 AM

ok, so i did a bit more board reading, and i'm still left with one question. I see that this processor runs at 333x9=3ghz, and i see that DDR2 667 runs at 2x333, and I also see that a motherboard with a FSB works at a speed of 4x333. So yes, I see the 333 in all these factors. What i don't understand is related to my original question involving DDR3-1333(PC3-10600). People are talking about using DDR2-667 because it would run in sync with the e8400 processor, but isn't this only utilizing half of the thruput of a 1333Mhz FSB motherboard? Everyone I read is almost making it sound like there is no difference between a 667Mhz FSB and a 1333Mhz FSB. To truly , synchronously utilize a 1333Mhz FSB, don't you need 1333Mhz(PC3-10600) memory ?
May 27, 2008 2:04:16 AM
May 27, 2008 2:15:07 AM

In fact, when you put the FSB:D RAM ration 1:1 in bios, the DRAM runs at 2xFSB. so for the e8400, the ram will run at 667MHz. If you overclock, you need faster ram ddr2 800 is so cheap, don't bother to buy 667MHz in particuliar for the e8400.

by the way, you can set different ration in bios so if you want to run the ram at 800 MHz, you can set the divider to 6:5 (333*6/5 = 400) but it's not in sync with the FSB. The impact ? I don't really know. but maybe the gain on the speed will be handicaped by the out of sync.

Sure the ideal willbe to run ram at 1333MHz, but it's too costly for the benefit
May 27, 2008 2:35:08 AM

If the system bus is at 333 then ram will run double that, and the FSB will run 4X that. If you are using DDR2 1333 ram at its FULL potential, that means the FSB would be running 2666 at a 1:1 ratio. The 1333 is for people who run the ram out of a 1:1 ratio and try to clock it as high as they can.
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