Question about bus speed and ram.

By sc0rchedst0rm ยท 6 replies
Feb 27, 2007
  1. If my mobo has a bus speed of 1066 MHz, and DDR2 RAM, should I be putting in 533 MHz RAM? And would it make any serious difference if I was to put in something other than 533? If I put in 667, would it slow down to 533, or just not work?
  2. beef_jerky4104

    beef_jerky4104 Banned Posts: 822

    I'm sure that it would stay at 667. Even if you put in DDR2-800 it should stay at that speed.
  3. kitty500cat

    kitty500cat TS Evangelist Posts: 2,154   +6

    I'm not sure if 667 is any faster than 533, though, for the simple reason that 533 is in sync with the FSB, and 667 isn't. I'm not sure though.
  4. Didou

    Didou Bowtie extraordinair! Posts: 4,274

    Motherboards can have the FSB & ram run at different speeds but to "optimize" data transfers between CPU & memory, you should have them running in sync as suggested by Kitty. The only problem is that you would need to get DDR-II memory running at PC8000 (DDR-II-1066) for that & it's quite expensive.

    Also keep in mind that some motherboards can only use memory with speeds up to PC6400 (DDR-II-800) even though the FSB can be at 1066MHz.
  5. sc0rchedst0rm

    sc0rchedst0rm TS Rookie Topic Starter

    I took the current RAM out today when I had the chance, and it has a label on the side that reads 533Mhz DDR2. But my motherboards FSB is listed at 1066?
  6. KingCody

    KingCody TS Evangelist Posts: 992   +8

    Hi sc0rtchedst0rm, I understand why you're confused. there is conflicting information in this thread. I'll try to clear this up for ya...

    first you need to distinguish between actual speeds and effective speeds. for marketing reasons, you pretty much only see effective speeds and rarely see actual speeds listed on anything.

    • due to "quad-pumping", the effective FSB on a modern Intel system is 4 times the actual speed.
    • due to "double-data-rate", the effective speed of DDR and DDR2 RAM is twice the actual speed.
    • to run 1:1 FSB:RAM (sync) you only need to look at the actual speed

    • your motherboard's FSB is the maximum that your motherboard will officially support.
    • your motherboard controls the FSB, but it's default value is determined by your CPU.
    • your RAM's [533, 667, etc] speed rating is the maximum that the RAM will officially support.
    • your motherboard controls the speed at which your RAM will operate at, but it's default value is determined by the FSB and your RAM's SPD info (whichever is higher)
    • for optimal performance, you should run the RAM and FSB at the same actual speed. (a.k.a. 1:1, sync)

    as for your personal system, you haven't given any system specs (you should fill them out in your profile) so I don't know what you're using, but just as an example lets use an E6300 core-2-duo CPU. it has a default FSB of 266MHz (1066MT/s). to run your FSB and RAM in sync you would need DDR2-533 (or higher) which also runs at 266MHz (533MT/s).

    I hope that clears things up :wave:
  7. sc0rchedst0rm

    sc0rchedst0rm TS Rookie Topic Starter

    Thank you very much for the clear and concise explanation King Cody. Strangely, your example pretty much describes my set up. You also told me exactly what I wanted to hear, because I can get 2 gb of Corsair DDR2 533 at a discount price! So I'm pretty happy right now.
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