VIA K8T890 Series Chipsets

VIA's PCI Express implementation, which they're calling their 'Flex Express' architecture, is fairly flexible in that it has the ability to distribute PCI Express bandwidth across the North and Southbridge chips.  The K8T890 Northbridge is directly linked to 20 PCI Express lanes, and the VT8251 Southbridge has two of its own PCI Express links, for a total of 22 PCI Express lanes.

VIA's Flex Express Architecture Connections to the North and South Bridge...

When both the K8T890 Northbridge and the VT8251 Southbridge are used in conjunction, a total of 7 PCI Express devices are supported, with a total of 5.5GB/s of available bandwidth (11GB/s concurrently).  The total of seven devices is derived from the fact that 16 of the PCI Express lanes that are part of the Northbridge are used for the PEG video card slot, leaving 4 left to be used in up to four PCI Express X1 slots. The VT8251 Southbridge houses another 2 PCI Express lanes, adding two more PCI Express X1 slots, for a total of 7 devices (Graphics + 6 PCI Express X1 peripherals).  It's not likely that we'll see many K8T890 powered motherboard setup in this configuration for quite some time, however, as PCI Express X1 cards have yet to emerge in any quantity.  Standard PCI slots will be common for the foreseeable future.

This type of distributed setup is beneficial because high-bandwidth devices, like a Gigabit Ethernet controller for example, can be connected directly to the Northbridge, while less demanding peripherals can be connected to the Southbridge.  We should also note that the K8T890 Northbridge is compatible with all past VIA Southbridges, and should be compatible with future Southbridge chips as well.  So the total number of PCI Express lanes, and the entire feature-set for that matter, could change in future versions of the K8 series chipsets.