Read on for the scoop on all of VIA's new chipsets, plus performance test results for the enthusiast-oriented PT894 chipset.
The new logic
As you may know, core-logic chipsets are generally modular beasts, with various functional units inside each chip. For these new chipsets, VIA has cooked up several technologies and incorporated them into three new north bridge chips plus a new south bridge. The north bridges share some common elements, including:
PCI Express support PCI Express, of course, provides dedicated, point-to-point connectivity for graphics cards and other peripherals. The number of lanes of PCI Express support varies among the three north bridges, as I'll explain below.
A flexible new memory controller Like Intel's 900 series, the new VIA memory controller can support both DDR and DDR2 memory, at speeds up to 667MHz for DDR2. Unlike Intel's 925X and 925XE chipsets, though, the higher echelons of VIA's chipset line will not be stripped of their support for DDR memory. Given the current price-performance proposition for DDR2 RAM, that's a very good thing.
Support for bus speeds up to 1066MHz All of VIA's new north bridge chips are slated to get support for a 1066MHz front-side bus. In reality, however, this support is complicated by a number of mitigating factors. First, VIA readily admits that getting the timing right between a 1066MHz bus and high-speed DDR2 memory is presenting them with some difficulty. Second, Intel hasn't been comfortable enough with the 1066MHz bus to allow anything but its rare-as-hen's-teeth Pentium 4 Extreme Edition processors to support this bus speed. One of the reasons Intel cites for holding back is the trouble it's had getting its CPUs to run reliably with a 1066MHz bus.
Still, I'd expect to see a 1066MHz bus speed option on new VIA-based Pentium 4 motherboards. Those boards also shouldn't be hampered by the anti-overclocking measures that Intel built into the 915 and 925X chipsets, so that faster bus speed might be a useful option to have.
A new process and package VIA's new north bridges will be manufactured using a 0.15-micron fabrication process, down from 0.22 microns for the original PT880 chipset. VIA has also transitioned to a new flip-chip package for these chips to allow for higher memory controller speeds. (The K8T890 for the Athlon 64 will remain in a wirebond package.)
Two lanes of PCI Express connectivity The VT8251 will augment the north bridges' PCI Express capabilities with two PCI-E lanes of its own. Each lane will very likely be used to power a PCI-E x1 slot or onboard peripheral.
Full SATA II The VT8251 will include four SATA ports, with support for device hot plugging, Native Command Queuing, and 3Gb/s SATA-II transfer rates. The support for higher transfer rates will give the VT8251 a leg up on Intel's ICH6. VIA also touts its support for SATA port multipliers; these are new adaptors that allow one to connect up to 16 devices to a single SATA port. Obviously, the performance of such a solution won't be stellar, but they should allow for very large amounts of storage connected to a single PC. Also, 3Gb/s transfer rates might come in handy in such a scenario.
RAID 5 support VIA's DriveStation RAID capabilities will get an upgrade in the VT8251 with the ability to create and use three-drive RAID 5 arrays. This feature comes in addition to the usual RAID 0, 1, 0+1, and JBOD flavors of RAID that the current VT8237 already supports. RAID 5 generally involves some CPU overhead for parity calculations, but it does offer a nice combination of performance, data integrity, and total array capacity. The VT8251 will rely on the CPU to handle parity calculations, so we'll have to test it and see how it performs. Personally, I am a big fan of RAID 0+1 or, even better, RAID 10, but RAID 5 for no extra cost on an enthusiast mobo should be nothing to complain about.
The VT8251's RAID support will also include cross-controller array spanning, so that one could potentially build an array using one SATA drive and one ATA/133 drive, as NVIDIA's nForce4 allows. VIA also plans to offer the ability to allocate a hot-spare drive and, like the nForce4, a RAID morphing feature that will let users switch array types on the fly without loss of data.
High Definition Audio The VT8251 will include what VIA is calling Vinyl HD Audio, which is essentially support for Intel's new High Definition Audio standard. HD Audio allows for samples rates up to 192KHz at up to 24 bits of precision. The ability to push more bits through is not, by itself, the key to true high-definition audio, but it is a good start. Judging by the current implementations of Intel's 900-series chipsets, the codecs and motherboards still need some work, though.
VIA will continue offering Vinyl Audio Gold, which bypasses the south bridge audio capabilities and uses VIA's Envy24PT audio controller chip, instead. Also, all flavors of Vinyl Audio are getting QSound support in their drivers, replacing the Sensaura algorithms formerly used.