The SiS 645
Unlike VIA, SiS has Intel's blessing to produce its DDR chipset for the Pentium 4. SiS licensed it fair and square, and what SiS has done with that license is, at least on paper, quite impressive.

The 645 chipset includes support for the standard range of features, and it has many of the same specs as the 845 and P4X266A, right down to an IOQ depth of 12. However, the 645 has two stand-out features: support for 333MHz DDR memory (also known as PC2700 memory, in marketingspeak) and an interconnect between the north and south bridges of the chipset that's twice as fast as the competition.

The 645's support for 333MHz DDR SDRAM is the biggest deal, of course. DDR333's combination of high memory bandwidth (2.7GB/s) and low latencies (unlike RDRAM) might well be best of all worlds for memory right now. SiS has lined up a long list of memory manufacturers who have endorsed the SiS 645 at launch and promised to support it with 333MHz DDR memory. SiS is out on the leading edge of the standards process here, though, and DDR333 isn't really widely available just yet. VIA claims they will support DDR333 when the time comes, but not yet. Nonetheless, it is possible to purchase DDR333 DIMMs from a select few manufacturers, so we'll test it here today and see how it performs. We'll also test with 266MHz memory, for comparison's sake.

SiS's bandwidth bonanza also extends to the link between the 645 north bridge chip and its companion, the 961 south bridge. At 533MB/s, SiS's proprietary MuTIOL provides twice the bandwidth of Intel's Hub Architecture or VIA's V-Link. SiS makes a somewhat compelling argument for MuTIOL's extra bandwidth. In extreme situations, the amount of I/O traveling through a south bridge chip can exceed 266MB/s.

SiS has been on something of a roll lately with their highly-regarded 735 chipset for the Athlon. If they can stake out the technology lead in Pentium 4 chipsets and hold their ground, SiS may be able to take another big step forward.