Some "high density" 133 MHz ram won't work in older chipset motherboards. For example, Kingston Value Max 133 MHz /256 MB ram, which has chips on only one side of the memory stick, won't work in an Abit BH6, a BX-chipset motherboard. But PNY Technologies 133 MHz/ 256 MB ram , which has chips on both sides of the memory stick, will work in the BH6. Both types will work in more recent chipset motherboards.