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VIA's K8T800 Pro chipset

Primed for Socket 939

VIA'S ATHLON 64 CHIPSET, the K8T800, has dominated the Athlon 64 scene since the processor's launch last fall. Right from the beginning, we found the K8T800 to be a fast, stable solution that outperformed its only real competition, the NVIDIA nForce3 150. Not only that, but the K8T800-based MSI K8T Master2 put in a stellar showing in our dual Opteron workstation motherboard round up not long ago.

Mated with VIA's VT8237 south bridge chip, the K8T800 offers support for AGP 8X, Serial ATA RAID, USB 2.0, six-channel audio, and the usual litany of checklist features common to today's core-logic chipsets. Short of an all-out conversion to PCI Express, what more could anyone want out of an Athlon 64 chipset?

The K8T800 Pro
Two things, apparently. VIA has decided to make a pair of useful modifications to its north bridge before AMD's new Socket 939 processors arrive in force, and the K8T800 Pro is the product of those changes. First, VIA has made the AGP and PCI clocks on the K8T800 Pro run independently of the clock for the HyperTransport link. (There is no traditional front-side bus on an Athlon 64, but the north bridge talks to the CPU via HyperTransport.)

For everyday operation at stock clock speeds, this new clocking scheme doesn't mean much. However, by making these clocks run asynchronously, VIA is delivering a big, juicy gift to overclockers everywhere, whose Athlon 64 overclocking ambitions have been frustrated by motherboards incapable of running at higher bus speeds. Now, newer versions (including Socket 939 editions) of excellent boards like the Abit KV8 MAX3 and MSI K8T Neo should offer much more flexibility for those of us looking to subject an Athlon 64 2800+ to sweet, egregious abuse.

A block diagram of the K8T800 Pro chipset. Source: VIA.

Second, the K8T800 Pro supports HyperTransport clock speeds of 1GHz. That means the north bridge talks to the CPU even faster than before. Now, follow along with me here. The K8T800 had a pair of 16-bit, 800MHz HyperTransport links—one running in each direction—between the CPU and the north bridge, for theoretical peak bandwidth of 6.4GB/s. The K8T800 Pro has a pair of 16-bit HT links between the CPU and north bridge that can run at 1GHz clock speeds, giving it a theoretical peak bandwidth of 8GB/s.

The trick to the 1GHz HyperTransport link, by the way, is a 5X multiplier on the HyperTransport clock. The HyperTransport link will still show up in the BIOS as a 200MHz "LDT bus" or "front side bus," but the available multipliers won't top out at 4X any longer. The nominal clock rate will remain 200MHz. The 5X multiplier for HyperTransport isn't yet officially supported by AMD, but our rather ancient Athlon 64 FX-51 ran with nary a complaint using a 5X multiplier on the K8T800 Pro reference board. Rumor has it AMD will give 1GHz HyperTransport its official blessing when Socket 939 processors arrive.

Trouble is, nothing much is taxing the K8T800's 800MHz HyperTransport links as is. 6.4GB/s is more than enough bandwidth for communication between the north bridge and CPU at present, because AMD has moved the memory controller onto the Athlon 64 itself. All that's left is I/O traffic and AGP communications. I suspect 1GHz HyperTransport will matter more when PCI Express arrives, but for now, the K8T800 Pro has this feature in case it's needed. (Ok, so 1GHz HyperTransport could be useful now in a multiprocessor Opteron chipset, too, but I don't believe the CPU-to-CPU links are dictated by chipset considerations.)

So that's the skinny on the K8T800 Pro chipset. There's nothing too earth-shattering involved, but it is an evolutionary product that will likely be at the heart of scads of Socket 939 motherboards.

What's missing from the K8T800 Pro? Either nothing or lots, depending on your perspective. Coming soon on the chipset front are all kinds of new features, including PCI Express, the new High-Definition Audio standard, more and faster Serial ATA RAID channels. NVIDIA has also added Gigabit Ethernet and a firewall to the nForce3 250Gb, the K8T800 Pro's main competition. This chipset has none of those things. But in high tech, I suppose every product is part of the journey, none a destination.

Some prose on Pros
This section of the review is intended to undo the work of the marketing people, specifically with respect to the "Pro" or "Professional" tag. VIA has added the "Pro" tag to the end of the K8T800 name in order to identify this chipset as the one with the two tweaks described above. This has nothing whatsoever to do with whether the chipset is intended for use in Athlon 64 or Opteron systems. Both the K8T800 and K8T800 Pro are equally at home in sweet, sweet dual Opteron motherboards and low-end Athlon 64 boards.

NVIDIA, however, has elected to use the "Professional" label a little bit differently. The nForce3 150 is NVIDIA's Athlon 64 chipset, while the nForce3 Pro 150 is the Opteron-oriented product. How are they different from one another? The name, mainly, and perhaps the price—but not the silicon.

Just so that's clear to everyone.