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Three bridges
The PT880 Pro will hit store shelves first, by all accounts, and will probably be the most popular of the three north bridges, at least for the first half of this year. True to its name, the PT880 Pro doesn't change much from the original PT880 chipset. Like the PT880, it supports AGP 8X graphics cards. The big news here, however, is that it also supports PCI-E graphics cards—at the same time. VIA says the PT880 Pro works just fine with a duo of graphics cards, one AGP and the other PCI-E, operating simultaneously in 3D applications on different displays.

Expect to see PT880 Pro motherboards sporting a pair of graphics slots, one AGP and the other PCI-E. These beasts of transition may also have two different types of memory slots, allowing users to take their pick of DDR and DDR2 memory, as well.


Block diagram of the PT880 Pro chipset. Source: VIA.

Gigabyte's board seems to be a typical example of a PT880 Pro mobo. It will pack four-phase power, bus speeds up to 1066MHz, AGP and PCI-E graphics slots, and both DDR and DDR2 memory slots. Because it has the older VT8237 south bridge, the board will not include HD Audio, RAID 5, or any PCI-E x1 slots. Gigabyte expects its PT880 Pro motherboard to enter mass production in mid to late February, with boards available in retail by late February or early March. Epox and Abit are planning dual graphics mobos based on the PT880 Pro, as well.


Abit's VT8 has both AGP 8X and PCI-E x16 slots

VIA says its pure PCI Express chipsets, the PT894 series, will arrive "soon" after the PT880 Pro. The PT894 will go head to head with Intel's 925X and 925XE chipsets on features, so it will drop AGP graphics support and instead add more PCI Express lanes, for a total of 18. In addition to 16 lanes for PCI-E graphics, the PT894 north bridge will be able to drive a pair of PCI-E x1 slots for peripherals, and these x1 slots should feature somewhat lower latencies than would PCI-E slots hanging off of the south bridge. Of course, the PT894 will only really challenge Intel's 925XE feature for feature when it gains the assistance of the VT8251 south bridge, which has two more lanes of PCI-E capability.


Block diagram of the PT894 chipset. Source: VIA.

The most intriguing of all of VIA's new chipsets is the PT894 Pro. This chipset will bring dual PCI-E graphics slots to Pentium 4 motherboards, a la NVIDIA's SLI—or at least that's the plan. The PT894 Pro north bridge supports 20 PCI Express lanes, and VIA plans to allocate them all for graphics. PT894 Pro motherboards will include two physical PCI-E x16 slots. To the primary slot will flow a full 16 lanes of PCI-E goodness. The secondary slot will get four lanes. VIA has no plans to require mobo makers to include PCI-E rerouting cards or jumper blocks. In order for PT894 Pro mobos to include any PCI-E x1 slots, the PT894 Pro north bridge will have to be used in conjunction with the VT8251 south bridge.


Block diagram of the PT894 Pro chipset. Source: VIA.

VIA believes the PT894 Pro is fully capable of supporting NVIDIA's SLI technology, save for the fact that NVIDIA's drivers preclude such a thing. NVIDIA is apparently in no hurry to allow a competitor's chipset to work with SLI. VIA seems to be banking on cracking into the SLI market eventually, but in the meantime, they are talking a good game about running dual graphics cards with four monitors and the like. Such things have been possible for a long, long time with the use of PCI graphics cards, though. The real reason for the PT894 Pro to exist is SLI (and perhaps ATI's answer to SLI.)

I'm curious to see how long NVIDIA will try to keep other chipset makers out of the SLI business, especially once mobo makers start building PT894 Pro motherboards. We may be waiting four or five months for the first PT894 Pro boards to arrive, however, given the time frames we're hearing on the initial wave of PT880 Pro boards.