Which of these memory specifications you can put to use depends almost entirely on the motherboard chipset. All motherboards will have some method of adjusting the CAS and RAS timings, but the ability to change memory clock speeds differs greatly between chipsets. Older chipsets such as the Intel BX will only function at a memory frequency equal to the system front-side bus, and only fully supports the 66 and 100 MHz FSB speeds.

Newer motherboard chipsets such as the VIA Technologies KX133, KT133 and Apollo Pro 133/A support asynchronous memory frequencies, allowing PC133 operation even when using the 100 MHz FSB, or vice versa. The ability to increase or decrease the memory speed relative to the system bus is a powerful feature and allows unprecedented control over memory performance. The Intel i815 and i815E is much like an enhanced BX chipset, and only supports PC133 speeds when using a matching 133 MHz system bus and CPU.

The System BIOS is where the CAS latency, RAS-to-CAS delay, and RAS precharge time options are found, and it is usually where the memory frequency selection is as well. In select instances, the memory frequency must be set using an onboard jumper or switch, so please consult your motherboard manual for specific information on your specific PC. Here is an example of one popular format, with all of the relevant memory options highlighted.

In most motherboards, the CAS and RAS options will be in the Advanced Chipset section, though again, consulting your documentation is probably the best idea. Each of these settings should have available menu selections of 2 or 3. If you are already operating at 2-2-2 (CAS - RAS/CAS Delay - RAS), then the BIOS options have been set as high as they will go. Those operating at 3-2-2 or 3-3-3 may have some room to maneuver, depending on the both the memory rating and FSB speed. Depending on the BIOS, there may also be an option for SDRAM Cycle Time, with choices of 5/7, 6/8 or 7/9.

Unlike CPU or video card overclocking, adjusting the memory timings and frequency settings offers little physical risk to your system, other than the possibility of a crash or program failure while testing. The memory will either be able to handle the higher settings or not, with none of the accelerated decrepitude issues associated with raising a chip's core frequency. Also, as opposed to CPU tweaking and overclocking, there is little danger of setting the memory timing or frequency too high, resulting in a system that refuses to boot. Using a variety of current motherboards, even 10 ns PC100 SDRAM was able to boot at 2-2-2/ PC133 speeds, but immediately locked up during the OS load.