Can I use PC133 or PC100 SDRAM in my PC that has a 66MHz front side bus?

All SDRAM is backward compatible and can run at any bus speed slower than it is rated to run.<br />
<br />
For example, a PC133 SDRAM DIMM is capable of running at 133MHz, 100MHz, and 66MHz. There are a few older motherboards that require 66MHz SDRAM and that will not accept PC100 or PC133 SDRAM, but they are the exceptions to the rule.<br />
<br />
Keep in mind that your memory run will only run as fast as the slowest component installed. If you install PC100 memory on a system with a 66MHz front side bus, the memory will only run at 66MHz.