The first order of business is to determine if the BIOS settings currently match the specifications of your SDRAM. Some system vendors may not optimize BIOS settings, or something may have been missed during configurations. Either way, it never hurts to double check to see if there are any "quick wins" available through a simple change to the BIOS. If any of the memory BIOS settings are lower than your SDRAM specifications, then moving the one or more of the CAS latency, RAS-to-CAS delay, or RAS precharge time options from 3 to 2 can yield some noticeable memory performance benefits.

Of course, this refers to matching the memory specifications to the system BIOS settings. With most name brand memory, the SDRAM timing and speed ratings can actually be pushed higher, much as a CPU or video card can be overclocked past its rated speed. This is due to the strict rules in stating CAS/RAS timings, whereby all ratings are rounded up to the nearest whole number. Theoretically, you could have two sticks of SDRAM with true CAS Latencies of 2.1 and 2.9, and both would be labeled at CAS 3. As such, the amount of tweaking a specific stick of memory will handle varies greatly between brands, and even between model numbers from the same company.

As with CPU or video card overclocking, raising the memory timings should be done methodically and with ample time to test each adjustment. When adjusting these settings, the CAS Latency is both the most important, and most problematic, option to set. The recommended route is to start with the RAS-to-CAS delay and RAS precharge time options, moving them from 3 to 2 one at a time. Restart the system and make sure it is stable and boots to the operating system. Only then adjust the CAS Delay to 2 and be prepared to reset this option back to 3 if the experiment fails.

As far as the SDRAM Cycle Time option goes, benchmark testing did not demonstrate any noticeable performance difference between 5/7 and 6/8 settings. Logic would entail using the lowest cycle time that your memory can handle, but if stability issues do arise, then moving the option to a higher value should not have an adverse effect on overall system performance.

The ability to increase the memory frequency from 100 to 133 MHz is a bit more cut and dried than tweaking the CAS and RAS timings. With very few exceptions, PC100 SDRAM will simply not handle the 133 MHz memory frequency, even at low memory timings like 3-3-3. This is due to the inherently higher access times of most PC100 SDRAM, which may translate into required PC133 CAS and RAS settings of 4 or 5. Naturally, these numbers are out of spec and would negate using this memory at 133 MHz speeds. Some PC100 SDRAM may function on the 133 MHz frequency, but the chances are very slim.

If you do own PC133 SDRAM, then ensure that the system BIOS settings are correct. Motherboards based on the Intel i815 and i815E chipset run the system memory at a default speed of 100 MHz, even with the Auto speed selection activated and using a CPU on the 133 MHz FSB. But remember that even if the i815-based motherboard BIOS allows the 133 MHz memory frequency to be selected, it only kicks in with a comparable 133 MHz CPU such as the Pentium III EB or B variants.

Current VIA Technologies motherboard chipsets such as the Apollo Pro 133/A, KX133, KT133, etc., support asynchronous memory speeds, which means that a 133 MHz memory frequency can be used with a CPU running on a 100 MHz FSB. The system BIOS format for VIA motherboards vary between manufacturers, which range from the usual "+/- 33 MHz" to System/Memory/PCI ratios. Consulting your motherboard manual should explain the exact method used with your particular brand.

When first testing the 133 MHz memory frequency, it is advised to lower the CAS and RAS timings to 3-3-3 before raising the memory speed. This will ensure that the PC133 testing takes place at its lowest possible specification, and will reduce possible stability problems. After basic PC133 support has been confirmed, progress slowly through the steps outlined above in the Memory CAS/RAS Tweaking section.