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RAM Speed (mhz) and CPU question

By greyz
Sep 23, 2007
  1. im confused on how RAM and the CPU speeds work together. i thought it worked like this.. as an example if i have a Pentium 4 CPU that has 800FSB, then having RAM that runs at 800 mhz will make the system run at its best? i dont know if this is correct..

    i have a few examples on how it exactly works and id like somone to tell me which is right :)

    A. PENTIUM 4 800FSB, with 4 sticks of ram, each running at 200mhz (=800mhz) is this running at its best?

    B. PENTIUM 4 800FSB, with 1 stick of ram, running at 800mhz is this running at its best?

    C. PENTIUM 4 800FSB, with 2 sticks of ram, each running at 800mhz (=1600mhz) am i now bottlenecking because the CPU cant keep up with that speed?


    that is my theory.. i have no idea if this is correct, can somone tell me if this is how it works or am i wrong please?

    ive looked through the forum and cant find any info on this so sorry if its already been posted.
     
  2. BlameCanada

    BlameCanada TS Rookie Posts: 320

    Your slowest speed RAM stick will be the speed they all will work.

    You want RAM at the same speed and the highest speed that your mobo supports.

    Options B & C
     
  3. greyz

    greyz TS Rookie Topic Starter Posts: 20

    jjust to clarify this.

    so option C.. lets say if i have "4" sticks of RAM running at 800mhz each, the CPU will access ALL 4 of them at top speed? it has nothing to do with them all multiplied to 3200mhz?
     
  4. BlameCanada

    BlameCanada TS Rookie Posts: 320

    That is correct.

    Speed is just the width of the 'pipe'

    Adding pipes doesn`t increase the width of the whole pipe.
     
  5. Jase123

    Jase123 Banned Posts: 1,012

    yes that is correct greyz

    Your computer will " dummy " down your memory to match the speed of your slowest stick of memory. And its best to have one stick of 1gb ram than two 512 mb. This kind of acts like a buffer on your hard drive. Instead of having to go to two seperate glasses of water for a drink your computer only has to drink from 1.

    Regards Jase
     
  6. Rage_3K_Moiz

    Rage_3K_Moiz Sith Lord Posts: 5,431   +28

    I don't agree. The CPU is able to access pairs of RAM in parallel at the same time, so that would give much better performance than a single RAM stick. Ever heard of dual-channel? ;)
     
  7. greyz

    greyz TS Rookie Topic Starter Posts: 20

    thats another question i was about to ask! :D

    so it is true.. having dual channel memory combines memory speeds?

    example.. Pentium 4 800FSB /// with 2 sticks of RAM (dual channel) running at 400mhz.. therefor equals 800mhz for optimum speed with CPU.

    is that correct?
     
  8. system7

    system7 TS Rookie

    You want to run CPU-Z to find out what's going on here. DDR400/PC3200 runs at a bus speed of 200MHz. The FSB of the processor is 800MHz, so the memory controller does 4 memory reads per cycle in the Intel world. Memory configuration depends on the chipset and memory type.

    The optimal configuration on Pentium 4 Intel chipsets up to the 915 is 4 identical sticks of DDR400. Two matched PC3200 sticks running as a dual-channel pair give an optimal bandwidth of 6400 MB/s to the processor, and having 4 identical allows some furthur minor tricks like Bank Interleave and performance mode to speed things up.

    I believe you can run DDR2-800 PC2-6400 memory with 975 chipsets, dual-channel as well, but I don't know if that is really any faster in practise. Latency worsens as speed goes up. You think this is complicated, AMD stuff gets worse...:haha:
     
  9. Tedster

    Tedster Techspot old timer..... Posts: 6,000   +15

    please read the upgrading ram guide in the guides forum.
     
  10. greyz

    greyz TS Rookie Topic Starter Posts: 20

    thank god i dont want AMD :D tyvm everyone
     
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