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Question: Which Memory speed matches the FSB?

Last response: in Memory
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June 19, 2008 9:34:14 AM

I have been searching google as well as various forums for the last 2 hours, I cannot find a straight answer. It's probably a dumb question but here goes...

What memory speed do I need to match an Intel Core 2 Duo E8500 (2 x 3.16 GHZ) 1333FSB - 6 MB?

I've been baffled by articles that try to explain dividers and what not, all I want to know is the speed which matches the processor.

If someone could answer in the most basic terms. Eg. 1333FSB can use a memory speed of X. I would be most grateful.

Any background info on which speed to choose also would be much appreciated.

Many Thanks :) 
June 19, 2008 9:53:51 AM

667Mhz which is pc2-5300, ill edit in a few minute to explain a bit more (done)

First you have to divide the FSB of the CPU by 4 to get the real FSB (since it does 4 cycle every clock or something like that). So the FSB will be 333.25.

Then to find matching RAM, you must multiply the FSB by 2 (because it's DOUBLE data rate aka DDR) so you get 666.5, so 667mhz to get a 1:1 synch.

But you could always run it unsynched and use pretty much any ram speed higher than 667mhz.
a b } Memory
June 19, 2008 12:22:57 PM

The Front Side buss is 4 operations per cycle - so your 1333 is actually 333 x 4

Memory runs two operations per cycle - 333 x 2 is 666


As far as what RAM to buy: If you are not overclocking, then all you need is DDR2 667. If you *are* going to overclock, decide your target Front Side Buss speed and buy memory that runs at the proper speed for your target.




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June 19, 2008 3:33:34 PM

Many Thanks, this was exactly the information I was looking for.
June 19, 2008 4:23:14 PM

Sorry to hijack this thread , but there wont be apoint making a new thread since its related.
I'm a noob at this intel stuff , so what is the point of running 1:1 ratio or whatever. So if my E7200 is running 1066 i have to underclock my 800 ram to 533 ?
June 19, 2008 4:58:29 PM

Xternal said:
Sorry to hijack this thread , but there wont be apoint making a new thread since its related.
I'm a noob at this intel stuff , so what is the point of running 1:1 ratio or whatever. So if my E7200 is running 1066 i have to underclock my 800 ram to 533 ?

That would give you 1:1 yes..but it's not necessary.
June 20, 2008 10:14:41 PM

x: it's just that you won't see any significant performance increase by running the memory bus any faster, since all data to/from the RAM has to go through the FSB as well. If you don't match the FSB and memory bus data rates, one will bottleneck the other.
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