Sometimes the video card’s memory chips are running at a speed that is lower than their maximum. For example, you have a video card with a memory chip capable of running up to 500 MHz, but the memory is being accessed at 450 MHz.

If you were lucky to get a card like this, you will find that the memory is highly overclockable. This happens because you will be able to put the memory running at a higher clock rate but still under its specs, and then push the memory over its specs.

First you need to know the maximum clock rate of the memory chips of your video card. You can discover this by taking a close look at the chips. The speed grade is marked on the chip’s body after a dash (ex: -40, -50, -5, etc.) as a number. This number is the memory clock, measured in nanoseconds. To find out the maximum clock rate in megahertz, divide one thousand by this number. In the case of two-digit numbers like 40, 45, and 50, place a decimal point between the two digits. For the calculation, you would use 4.0, 4.5 and 5.0, respectively. There is one exception: memory chips from Samsung labeled as “2A” actually are 2.8 ns chips, not 2 ns chips.

Pay attention, because the number you will find is the real memory clock, not its DDR speed, which is the double of the number you will find.

Let’s give you a couple of examples to clarify this. In Figure 6, you see two of the memory chips used on our GeForce 6800 GS. They are labeled as 2 ns, so their maximum labeled clock rate is 500 MHz (1,000 / 2). As we discussed previously, on this video card the memory was accessed at 500 MHz, so in this case the memory was already working at its maximum labeled speed. Of course, we can try to put it to work above its specs.

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Figure 6: 2 ns (500 MHz) chips from Samsung

In Figure 7, there is one of the memory chips from a GeForce 7900 GT. As you can see, it is a 1.4 ns chip, meaning that it can officially run up to 715 MHz. Since on our GeForce 7900 GT the memory was accessed at 660 MHz, we know that we can push the memory clock up to at least 715 MHz and that the video card will still work well, as the memory clock will remain inside the chips’ official specs. We can still try pushing the memory clock even higher for a real overclocking.

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Figure 7: 1.4 ns (715 MHz) chip from Samsung

On the next page, we will present some tricks that can help you achieve a higher memory clock.