Effects Of Overclocking: ATI
Even in 2D mode, the video memory of the Radeon HD 4870 always runs at its full clock speed. Using a tool like RivaTuner, you can underclock the graphics chip, resulting in savings of up to 22 watts. The card also runs 5 degrees Celsius cooler. This has no effect on its noise level, though, since the fan speed profile doesn’t slow the fan down.
In 3D mode, power consumption can increase by up to 14 watts as a result of overclocking. The cooler is able to keep the card’s temperature constant, compensating for the higher heat generation by turning up the fan speed. The not-so-pleasant side effect is an increase in noise, jumping from a comfortable 40.6 dB(A) to a more unpleasant 46.4 dB(A) at maximum speed. At medium loads, the fan exhibits an uneven noise level. When the card reaches a temperature threshold of 70 to 71 degrees Celsius, the fan spins up, only to slow down once the temperature drops below 67 degrees, until it hits 70 degrees again.