With the introduction of the Intel 820 chipset, using Rambus memory, we now have the ability to run the memory bus at various speeds. Note that the 820 chipset supports both SDRAM and RDRAM. Click here for more details. The 100MHz memory bus is for SDRAM, while the 300/356/400MHz is for Rambus PC600, PC700, and PC800, respectively. And notice with the 820 chipset, it no longer supports the 66MHz CPU/host bus. This mean the Intel Celeron processors (those running at 66MHz CPU bus) are not supported by this chipset.

Due to the high cost of Rambus memory, Intel is refocusing on SDRAM technology with their upcoming 815 chipset. Intel will increase the memory bus from 100MHz up to 133MHz. This mean 815 systems equipped with PC133 SDRAM will benefit from a small performance increase.

Lastly, there is a new SDRAM technology emerging called DDR-SDRAM. DDR stands for "double data rate" SDRAM. In layman's term, this can effectively double the speed of PC133 SDRAM to 266MHz. It does this by NOT increasing the memory bus speed, but by allowing data to be transferred at both the falling and raising edge of a memory cycle. Current PC66/100/133 SDRAM is only able to move data at either the falling or raising edge of the memory cycle. DDR allows SDRAM to move data at both edges, which can double the memory transfer without having to increase the memory bus speed.

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