Building a new PC, what speed memory do I need, and why?

I'm building a new PC based off the E6850 intel CPU. It has a FSB of 1333. I'll be getting a Motherboard similar to this one which is rated to accept CPU's with a FSB of 1333 and actually run at that speed.

Now the part I'm having a difficult time figuring out is what speed ram I need and why. It seems that most people are putting DDR2 800 in their PC's when using the 6850 for their CPU.

I know that you want your ram to sync with your FSB at a 1:1 ratio for optimal performence and that if your ram is faster than your FSB it will automatically scale down to that 1:1 ratio. How does DDR2 800 sync up with a 1333 FSB though? What multipliers do they use nowadays to figure this stuff out?

I don't plan on overclocking so I want to get ram that will be at a 1:1 ratio with my 1333 FSB.

Thanks for your help!
9 answers Last reply
More about building speed memory need
  1. 666MHz memory will allow for a synchronized clock between the memory and CPU. The memory is double pumped 333X2 and the CPU FSB is quad pumped 333X4. Most people buy the 800 memory so that they can overclock or drop their memory timings since the prices are very close.
  2. so you multiply your ram's Mhz rating by 2 to know what FSB it syncs with?
  3. That is correct in this case.
  4. Well, technically, you would divide the RAM frequency by 2.

    It is a matter of (confusing) definitions.

    Using an E6850 for example:
    FSB frequency is 333 MHz.
    CPU freq = FSB freq X internal mult = 333 MHz X 9 = 3.0 GHz
    FSB clock = FSB freq X 4 = 1333 MHz
    DDR2 clock = FSB freq X 2 = 667 MHz

    Using an E6850 moderately OC'd for example:
    FSB frequency is 400 MHz.
    CPU freq = FSB freq X internal mult = 333 MHz X 9 = 3.6 GHz
    FSB clock = FSB freq X 4 = 1600 MHz
    DDR2 clock = FSB freq X 2 = 800 MHz

    And you should be able to do that with the stock cooler or an inexpensive AC 7 Freezer Pro.

    And like Jim said above: With prices of DDR2-667 and DDR2-800 so close, buy the faster memory.
  5. A processor FSB is quad pumped. In your case 333x4=1332 which they call 1333. As stated above, ram is double pumped. 333x2=666 which they call 667.

    In short, what you are trying to match with a 1:1 ratio is the base FSB of 333. Folks that opt for DDR2 800(400 base FSB), do so for various reasons, but one of the most common are: overclocking the CPU FSB to match the faster ram. In your case this would effectively OC the CPU to 3.6ghz with the E6850 standard multiplier of 9.

    Just a side note, so far the 680i MBs do not appear to be upgradeable to the next generation Penryn processors. It is also insanely overpriced. If you are going to spend that kind of money, one of the newer X38 MBs would be a better choice although it supports Crossfire instead of SLi.
  6. How is the motherboard you linked to compatible with the new Penryn cpu's coming out? It's the same socket type.. isn't the penryn going to be using a new socket type?
  7. No at CPU. Get a Q6600 or an E6750 with a Arctic Cooling Freezer 7 Pro, overclocked to 3.0 Ghz.
  8. Well the original motherboard I linked is socket 775.. so guess I'll go with the one that allows me to have the choice of using SLI
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