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    CPU and RAM speed mismatch

    Discussion in 'Hardware Components and Aftermarket Upgrades' started by ramgen, Aug 4, 2008.

  1. ramgen

    ramgen -- Morgan Stanley --

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    Hey Guys,

    I have a brief question: When we had i915pm chipsets long ago (around 2005) it was supporting both 533MHz for the RAM and for the FSB of the CPU. However later with the 965 chipset, the imbalance showed up and it started to support 667MHz for the RAM and 800MHz for the FSB of CPU. Today the latest PM45 chipset supports 1066 MHz for the FSB of CPU and 800MHz of RAM.

    How much do you think this mismatch affects (essentially degrade) the overall performance?

    And the last question: Does the dual-channel RAM configuration alleviate this problem to some extent?

    Regards,
     
    ramgen, Aug 4, 2008
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  2. powerpack

    powerpack Notebook Prophet

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    Faster FSB compared to RAM is beneficial. Desktops have had faster FSB vs RAM bus for years. Much is said about the ratio. While that can make a difference do not think for a moment faster FSB vs RAM ever retards performance. If not a beneficial ratio might not gain much but will not suffer a hit.

    Dual channel per se does not alleviate the situation as you say. But I must say the way you ask and lay out is incorrect. A 800Mhz RAM should perform (bandwidth) better with 1066Mhz FSB vs 800Mhz FSB. So re state your question if you can?
     
    powerpack, Aug 4, 2008
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  3. flipfire

    flipfire Moderately Boss

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    Yes dual channels peak bandwidth will still overpower the CPU's FSB
     
    flipfire, Aug 4, 2008
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  4. Charr

    Charr Notebook Deity

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    Actually, in both cases the RAM is faster than the FSB. Intel he been using a quad pumped bus for a while (266 x 4 = 1066) while DDR2 is just doubled (400 x 2 = 800). Generally, higher RAM speeds than the FSB (or HTT) constitute good performance. If the bus outpaces the RAM, performace is hindered.
     
    Charr, Aug 4, 2008
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  5. ramgen

    ramgen -- Morgan Stanley --

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    Sure; so let's have 4 systems:

    A: 1066Mhz FSB, 1066MHz Ram (Dual Channel)
    B: 1066Mhz FSB, 800MHz Ram (Dual Channel) -- the PM45 case
    C: 800Mhz FSB, 1066MHz Ram (Dual Channel)
    D: 800Mhz FSB, 800MHz Ram (Dual Channel)

    Can you comment on the overall performance of these systems (i.e. rank them)? It is obvious that A is the best and D is the worst. How about A vs. B and A vs. C? How large are the gaps in between A-B and A-C?

    ================
    The alleviation of the mismatch by the dual channel configuration can be restated as:

    Let's have 4 systems:

    A: 1066Mhz FSB, 1066MHz Ram (Dual Channel)
    B: 1066Mhz FSB, 800MHz Ram (Dual Channel)
    A*: 1066Mhz FSB, 1066MHz Ram (Single Channel)
    B*: 1066Mhz FSB, 800MHz Ram (Single Channel)


    So in this case do the performance gaps in between A-B and A*-B* are equal percentage-wise?

    Thanks for your replies...
     
    ramgen, Aug 4, 2008
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  6. flipfire

    flipfire Moderately Boss

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    1066mhz FSB x 8bytes = 8.5gb/s peak bandwidth

    800mhz x 8bytes x dual channel = 12.8gb/s peak bandwidth

    Dual channel RAM is faster bandwidth-wise against the CPU's FSB
     
    flipfire, Aug 4, 2008
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  7. powerpack

    powerpack Notebook Prophet

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    Yea but guys regardless of what we are talking about (FSB and RAM) You will not get close to theoretical bandwidth. I am not really sure what our discussion is about? Dual channel RAM does not on a notebook exceed the theoretical bandwidth of single channel? What is the question?
     
    powerpack, Aug 4, 2008
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