The memory operates on managing signals from memory controller which produces the sequence of signals with some delays between them. These delays are necessary in order for the memory module to manage to perform the current command and prepare for the next one. Such delays are called timings and are usually measured in memory bus strokes. The following timings have got the biggest value: CAS# Latency (tCL), RAS# to CAS# delay (tRCD), RAS# Precharge (tRP) and Active to Precharge Delay (tRAS).
While BIOS setting by default, all necessary parameters of memory are set automatically. Each memory module has special chip called SPD (Serial Presence Detect) which contains optimal values for a particular module. To perform overclocking, you should turn off automatic memory setting and set all the parameters manually, and to perform the processor overclocking, you have not to increase a memory frequency, and vice versa, to decrease it.
The amount of available parameters for memory setting may vary a lot for different motherboards models, even performed on the same chipset. Most motherboards have a possibility to change a memory frequency and main timings that is quite enough for overclocking.
Those who like careful optimization and overclocking can choose more expensive motherboard with a lot of additional settings, and the means of manual setting of memory will be limited or be absent at all in the cheapest motherboards. The parameters of memory can be located in the section with overclocking settings, in the section “Advanced Chipset Features” or in one of subsection of a section “Advanced”.