There are two modes of configuring the memory clock: synchronous, were the memory clock is tied to the CPU external clock, and asynchronous, where the memory clock can be configured independently from the CPU clock. The mode your computer has depends on its motherboard.

The synchronous mode is usually found in entry-level motherboards while asynchronous mode is usually found in high-end motherboards. Also, notice that many low-end motherboards don't have any overclocking configuration at all.

So, how do you know what mode your motherboard uses? Enter setup, go to the "Frequency/Voltage Control" menu and pay attention on the available options. If you find any option to change the memory clock ("Memory Clock" or "Memory Frequency", sometimes under a sub-menu called "DRAM Configuration" or "Memory Configuration"), your memory is running at asynchronous mode. Otherwise it is running at synchronous. Also pay attention that in order to change clock configurations you may need to change the option that allows you to do so. This option can have several different names, like "Clock Control", "System Performance" or "DDR Timing Setting by". Sometimes memory configuration options are under "Advanced Chipset Setup" and not under "Voltage/Frequency Control", so you need to also take a look on this menu and look for memory configuration options there.

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Figure 1: This motherboard doesn't have specific clock configuration for memory. Thus the memory works on synchronous mode.

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Figure 2: This motherboard has a specific option for changing the memory clock, thus the memory works on asynchronous mode. You need to change "System Performance" to "Expert" in order to have access to the memory clock control.

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Figure 3: Memory clock options of the motherboard shown on Figure 2.

Let's explain in detail how do you overclock your memory.