The always controversial Rambus DRAM is not as poor of a purchase today as it was a couple of years ago. This is partially due to the presence of a processor that can actually take advantage of the bandwidth offered by RDRAM and also because memory prices in general have been spiraling downwards. A quick visit to www.pricewatch.com will tell you that the lowest price on a 256MB PC800 RDRAM module is 3.28x as much as the lowest price on a 256MB PC2100 DDR SDRAM (DDR266) module. Although this is somewhat reminiscent of the price disparity between RDRAM and SDRAM from two years ago memory prices have come down so much that we're talking about a difference of $57; two years ago it would have been $600.
The dramatic reduction in memory prices over the past 24 months softened the launch of the world's first Pentium 4 DDR chipset, VIA's P4X266. Although the performance of the P4X266 clearly approached that of the RDRAM based Intel 850 chipset, cost of memory wasn't as big of a reason to go down the VIA path as it once was. Another problem that was stacked against VIA was the touchy issue of licensing for their P4X266. If you ask Intel, the P4X266 should not be sold because VIA does not have a license to use the Pentium 4 bus. If you ask VIA, they don't need to strike a licensing agreement because of a prior agreement Intel made with S3, a large part of which is now a part of VIA. However, if you ask the most important players in this game, the motherboard manufacturers, most of them won't touch this situation with a 10ft pole. There are a select few that have released P4X266 based motherboards, but none of the major manufacturers have elected to go to production with their boards. It isn't that they don't have them ready, since virtually all of the major motherboard manufacturers have a P4X266 design; it's mainly an issue of waiting for Intel and VIA to sort things out.
Until recently, most motherboard manufacturers have only been able to take a "wait and see" stance on the issue of 3rd party chipsets for the Pentium 4 platform. In a move very reminiscent of their earlier launch of the 735 chipset, SiS has stepped up to the plate and offered motherboard manufacturers a very attractive solution. The 645 chipset is SiS' answer to the P4X266; and after recently going to production many manufacturers are finding themselves instantly attracted to it as it is the first Pentium 4 chipset to receive an official license from Intel.
As if legality wasn't enough, the SiS 645 officially supports DDR333 SDRAM; giving the Pentium 4 another 25% of what it likes the most: memory bandwidth.