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Does bandwidth matter on HD 3800?

Discussion in 'AMD / ATI' started by Spirou, May 14, 2008.

  1. Wile E

    Wile E Power User

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    That air is still cooler than the memory itself under load.
     
  2. P4-630

    P4-630

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    Then I probably have an unique videocard:D
     
  3. Wile E

    Wile E Power User

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    Possibly. On this 8800GT and my 2900XT, I have to dial back my mem OC when I put them on water.
     
  4. Spirou

    Spirou New Member

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    Did not find the time to do another series.

    Wether it's good to cool the RAMs with same heatsink may depend on its temperature. Mine isn't very hot. I still can touch my heatpipes at more than 900 MHz. GPU is between 40 and 45 C under heavy load.

    Heat isn't the only problem at higher memory clocks. There is noise on the bus, crossover and reflections at curtain frequencies. Not sure what can be done against that.

    Another problem is decreasing wattage per switching cycle is going along with increasing frequencies. This effect drives switching devices out of their calculated carrier saturation and they go into regulating mode instead of switching mode.

    Overvolting by square root of calculated overclocking multiplicator is needed for compensation.

    I can go from 1125 up to 1323 which is more than 15% oc on stock voltage but that's where saturation reaches its lower limit and artifacting steps in. Increasing memory voltage from 1.8V to 2.0V should give 20% higher clocking capability (1.11 * 1.11 = 1.21 cause current increases with voltage). That should work up to 1450 or 1500 MHz. Looks like some cards have Samsung 07s (0.71ns) and could go even higher than that.

    Another point is the voltage regulator section. Looks like some PBCs have much lower current capacities. Only half the coils on the single slot and toxic compared to the dual slot models and Atomic.
     
    Last edited: May 27, 2008

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