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VIA's KT400A chipset


As ever, A's the charm
— 7:00 AM on March 10, 2003

NVIDIA WAS SUPPOSED to take the Socket A chipset market by storm with its nForce chipset, but it didn't happen. Despite offering two channels of DDR memory and a host of compelling features, nForce's performance wasn't anything to write home about, and motherboard buyers looked elsewhere. NVIDIA's second effort at core-logic chipsets, however, has been much more successful. A reworked memory controller has given the nForce line a new lease on life. The nForce2 arrived a few months ago, and it's fast. Really fast—easily faster than the incumbent Socket A champ, VIA's KT400.

But VIA knows something about second efforts, too. Its second-revision chipsets, like KT133A and KT266A, have traditionally been notable improvements over the first revs. In fact, VIA's KT266A salvaged VIA's Socket A chipset line-up and helped seal the original nForce's fate.

Now that NVIDIA has been sitting on top for a few months, VIA is back with a new revision of the KT400 dubbed—you guessed it—KT400A. Created by the same lead engineer who designed the KT266A, this new chipset is intended as an nForce2 killer. But NVIDIA's challenge looks tougher this time around. Can VIA really match up with the nForce2? Is there room in the Socket A platform for VIA to squeeze out much more performance? Read on for the answers.


KT400A: It's all about the memory controller
The KT400A's only real change from the KT400 is a reworked memory controller in its north bridge chip. If you followed the rumors, you were probably expecting that. The surprise is that KT400A does not have a dual-channel memory configuration. The chipset just supports a single channel of DDR333 or DDR400 memory, very much like its predecessor.

Before you go writing off the KT400A as a non-event, though, listen up: VIA claims the KT400A is an nForce2-killer even without the second memory channel. They say because the Athlon XP's front-side bus is limited to 333MHz, there's no need for dual channels of DDR333 memory. The KT400A can supposedly perform just as well without the extra expense and trouble of a second memory channel.

To improve the KT400A's performance, VIA has reworked its memory controller significantly. (The rest of the north bridge, including the front-side bus, the AGP port, and the link to the south bridge, is largely unchanged.) VIA's marketing department celebrated this revamped memory controller by christening it with a new marketing name: FastStream64 Technology. The KT400A's FastStream64 memory controller includes "an expanded array of prefetch buffers to reduce latency in the memory controller," according to VIA's tech brief.

As you would expect, we're about to put those claims to the test with a battery of benchmarks punctuated by occasional smart-aleck comments. But before we do so, we should check out a couple of other changes coming down the pike from VIA which will affect the KT400A's fortunes.

Serial ATA in its native state: coming soon
The KT400A north bridge chip will begin its life paired up with the same south bridge chip as the KT400, the VT8235. That's no great problem, because the 8235 has nearly all the features the cool kids are wearing these days, including six-channel sound, ATA/133 support, and USB 2.0.

However, VIA has a new south bridge chip coming as soon as April, the VT8237, that will incorporate support for Serial ATA. (The regular ATA/133 controller will remain, too.) VIA points out that this will be the first south bridge implementation of Serial ATA, and as such, it will be the first Serial ATA controller to bypass the bottleneck of the PCI bus. The peak theoretical transfer rate of Serial ATA is currently 150MB/s, while a 32-bit, 33MHz PCI bus (the most common flavor in desktop PCs) is 133MB/s. By riding on a south bridge chip, VIA's Serial ATA controller will have 533MB/s of bandwidth available through VIA's V-Link chip-to-chip interconnect.

In fact, the VT8237 will support a new flavor of V-Link called V-Link Ultra that tops out at 1.06GB/s. The extra bandwidth will be useful, because the 8237 will support as many as eight USB 2.0 connections at once. Like the KT400A, the 8237 will be pin-compatible with its predecessor, so you can expect to see current KT400 motherboards arriving in new incarnations, first the with KT400A north bridge, and then with the 8237 south bridge.