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CPU FBS RAM speed relationship

Last response: in Components
April 24, 2009 10:36:37 PM

hey guys, new to this forum, i searched for an answer but i couldn't find anything with general information.

when building a PC, how should u consider the CPU FBS RAM speed relationship???

please and thank you!
April 24, 2009 10:46:18 PM

Nerd alert! I am not trying to give this guy an engineering degree, simplifications ahead!

The Front Side Bus is the base speed on the wires that connect everything else. It is assumed to be 200MHz unless something tells us different. Other components use multipiers of that speed for example. Double Data Rate memory speed is double that rate or 400MHz. DDR2 memory is Double Data Rate times 2 or 800MHz. The CPU might have a multiplier of 16. 200MHz times 16 equals 3.2GHz. In this case, if you raise the FSB by 1 it will have 4 times the impact on the memory and 16 times on the CPU.
April 24, 2009 11:09:00 PM

what about using these hardware that i currently have. (im pretty embarrassed about asking this question...)

Intel Core 2 Quad Q6600 Quad Core Processor LGA775 Kentsfield 2.40GHZ 1066FSB 8MB

EVGA Nforce 750I SLI Ftw LGA775 ATX DDR2 2PCI-E16 1PCI-E1 2PCI SATA RAID Sound GBLAN Motherboard
Front Side Bus:


OCZ Gold XTC PC2-6400 4GB 2X2GB DDR2-800

i didnt do any over clocking, did i match my hardware correctly?
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April 24, 2009 11:16:58 PM

Technically, the RAM is a little slow but if you aren't worried and don't plan to OC, I wouldn't worry about it. Ideally you would have DDR2-1066 RAM, (PC2-8500).
April 24, 2009 11:21:46 PM

first i want to thank you for your time!
Well, i took the ram out of my previous system to use in my new one.
I actually would love to have the knowledge of over clocking, but i will look into that (unless you can give me a quick tip on OC'ing my ram).

so because my ram is running slower than my cpu and FBS, does this affect my over all performance?
April 24, 2009 11:33:04 PM

Same here. I kept the RAM from my last system, 8G of DDR2, in favor of the minimal gains and possible loss from going to 4G of DDR3.

While it will effect benchmarks it really depends what you do with your system whether it's being hurt by it or not. If you're happy with the system as it is now just wait for 4G of 1066 to offer you a dance for under $40. ;) 
April 24, 2009 11:39:11 PM

hehe i can wait :p 

also, is it possible to OC my ram to get it to 1066MHz??
April 24, 2009 11:51:49 PM

It's *possible* But I wouldn't plan on it. The amount of variables would turn this thread into a text book. We have a seperate forum for overclocking here on Tom's. Start with the stickies at the top to get the basics out of the way then search the forum for overclocking DDR2-800.
a b à CPUs
April 24, 2009 11:57:15 PM

misry said:
Technically, the RAM is a little slow but if you aren't worried and don't plan to OC, I wouldn't worry about it. Ideally you would have DDR2-1066 RAM, (PC2-8500).

Actually, for a 1:1 ratio on a 1066FSB, you want DDR2-533. This is quite a bit slower than most current RAM, so 800MHz is actually above a 1:1 ratio in this case (which isn't something to worry about, honestly). The reason you want the RAM speed to be half of the effective FSB speed for a 1:1 ratio is because the RAM is dual data rate, meaning that the effective transfer rate (which is the reported frequency in most cases) is twice the true clock. Therefore, the true clock on DDR2-533 is 266MHz. The front side bus on all modern Intel CPUs (aside from the i7 of course) is quad pumped however. This means that it effectively transfers four times per clock cycle, and therefore, the effective transfer rate (the reported frequency) is four times the speed of the actual clock. Therefore, FSB-1066 has a true clock speed of 266MHz, just like the DDR2-533 mentioned above.

Now, as for the benefit of running 1:1? There isn't that much of a benefit at all, to be perfectly honest. You don't want to run slower than a 1:1 ratio, but running faster doesn't really harm (or help) things much in any way. Basically, 800MHz RAM is fine all the way up to FSB 1600.
April 25, 2009 12:13:19 AM

understood, thank you