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Pentium 4 DDR chipsets compared

Three new chipsets vie for supremacy
— 2:00 AM on December 17, 2001

PROPER SUPPORT FOR DDR SDRAM on the Pentium 4 platform has been a long time coming, in part of because of Intel's long-standing fascination with Rambus, and in part because of a legal dispute between Intel and VIA. Now Intel's own DDR chipset for the Pentium 4 is upon us, so we're rounding up a bevy of Pentium 4 chipsets to see which one is fastest. Will it be Intel's Rambus-driven 850? VIA's newly revamped P4X266A? Or the dark horse with the big muscles, SiS's 645 with support for DDR333 memory? Read on to find out.

Intel's 845 DDR
Intel's 845 chipset has been around for a while now; we first reviewed it back in September. However, the original 845 chipset and the motherboards based on it supported only PC133 SDRAM. This old, relatively slow type of PC memory isn't exactly well suited for a high-bandwidth platform like the Pentium 4, but that didn't stop the 845 from becoming a sales success. PC manufacturers latched onto the 845 as a cost-effective alternative to the Intel's 850 chipset and RDRAM. As the Pentium 4 pushed the Pentium III off of the desktop and out of the mainstream, the 845 became a common choice for corporate desktops and low-to-mid-range PCs.

That doesn't mean the 845/PC133 combination was a good choice, however. PC133 memory's low bandwidth squelched the best attributes of the Pentium 4—namely, impressive performance in 3D gaming and multimedia applications.

The 82845 MCH chip is packaged much like an older Pentium III

Meanwhile, we saw VIA's P4X266 chipset swoop into the void with support for DDR SDRAM. When we tested the P4X266 with a 1.6GHz Pentium 4, the DDR chipset performed at least as well as the 850/RDRAM combo. Only an Intel patent violation lawsuit against VIA, combined with a series of legal threats against motherboard manfacturers, kept the P4X266 from becoming the mainstream P4 chipset of choice.

Such tactics are the Rambus way, however, and they were largely effective this time around. Only a handful of mobo makers dared to launch P4X266-based boards, and Intel succeeded in starving the Pentium 4 of DDR SDRAM support, ostensibly to the benefit of RDRAM.

Intel's block diagram of the 845 chipset
What the devil is "10/100 Ethernet with AOL"?

Now Intel is bringing DDR SDRAM support to the Pentium 4 platform. There's still some odd ambivalence about it, however. Intel is unveiling the version of the 845 chipset capable of using DDR memory today. However, the official launch won't come until 2002. Intel is still claiming that RDRAM is the best choice for Pentium 4 performance, but they're also claming the 845 is Intel's fastest chipset ramp ever. The "845" designation was obviously chosen to denote slight inferiority to the RDRAM-oriented 850 chipset, but the 845 comes to market later and with some newer technology.

Go figure.

Whatever the case, Intel has apparently come around to the rest of the world's way of thinking—at least in practice, if not in theory—about the question of RDRAM versus DDR SDRAM. Everybody from graphics chipmakers like ATI and NVIDIA to chipset makers like VIA to, heck, the entire AMD Socket A platform has chosen to use DDR SDRAM instead of RDRAM.

Now that it's here, Intel's 845 chipset looks to be a solid product. Notice that I'm not calling the DDR-capable version of the 845 chipset the "845D", as many have called it during its development. Truth be told, Intel is just calling it the "845 chipset featuring DDR SDRAM." Apparently, now that the 845's DDR memory support is more or less official, only motherboard designs will determine the type of memory supported. Intel claims current 845 motherboards can be revised to support DDR memory with relatively little effort.

So what does the 845 chipset featuring DDR memory bring to the table? Plenty of performance-enhancing features. Allow me to geek out for a moment and give you some of the high points. Like the 850 chipset, the 845 has 256-bit internal data paths. That's four times the internal bandwidth of the Pentium III's 815 chipset. The 845 has a fairly deep In-Order Queue (IOQ) depth of 12, and it can keep 24 memory pages open at once. The 845 also includes a write cache. Finally, the 845's memory controller includes the ability to handle memory refreshes flexibly; memory refreshes are completed opportunistically, so memory strobes don't sap bandwidth.

In short, the 845 with DDR support is well equipped to take on its older brother, the 850 with RDRAM. More likely than not, the 845 will outsell the 850 by several orders of magnitude. But is it ready to take on the Taiwanese competition?