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VIA's PT800 and SiS's 648FX chipsets

Single-barreled shotguns

INTEL ROCKED THE Pentium 4 chipset market when it introduced its 875P and 865-series chipsets this past spring. These chipsets included support for a host of new features, including Serial ATA, RAID, dual channels of DDR400 memory, and an 800MHz front-side bus. The Taiwanese chipset makers who generally outfox Intel on new features were caught flat-footed, especially by the move to the 800MHz bus. However, VIA and SiS don't take long to incorporate new features into their chips, and they are poised to catch up with Intel in the next few months.

The first wave of response comes in the form of chipsets with 800MHz bus support and single-channel DDR400 memory controllers. These new chipsets, the VIA PT800 and the SiS 648FX, are aimed at the broad middle of the market, where dual-channel memory configs aren't necessarily worth the extra cost. SiS and VIA will no doubt aim to undercut Intel's prices significantly with these products, all the while arguing that single-channel memory solutions offer very decent cost-effective performance.

Naturally, we'd like to put that proposition to the test. We'd also like to satisfy our own sometimes-twisted curiosities. Could it be possible a second channel of 400MHz memory isn't necessary to get to most out of a processor with an 800MHz bus? Can VIA and SiS manage to make products that will stand out against the backdrop of Intel's impressive new chipsets? And, most importantly, can we make some really huge—I mean so huge, it's almost sick—graphs and tables about these new chipsets? Keep reading for the answers.

VIA's 12-gauge: the PT800
VIA's entry in the single-channel core logic sweeps is the PT800, a new north bridge chip mated to a new south bridge chip, with a full suite of features to bring it up to snuff versus the competition's latest. Of course, the folks in VIA's marketing department have been working overtime to coin and trademark new marketing terms to describe all of these features. The sheer onslaught of MarketingTermTM prowess is almost too much for our gentle reviewers' brains to handle, but we will try to associate all the appropriate chipset bits to the appropriate Hypers- and Ultras-.

The most important innovations in the PT800 already have their own names, of course. "800MHz bus" is pretty self-explanatory, as is support for a single channel of DDR400 memory. Unlike SiS, VIA has not yet introduced a north bridge with a dual-channel memory controller, instead arguing for the efficacy of low-latency single-channel solutions. On the Athlon platform, where VIA has had much success, that argument makes some sense, because the Athlon XP's bus runs no faster than DDR400 memory. Whether that argument will fly on the Pentium 4, however, is another proposition.

VIA gives its single-channel memory controllers a leg up by endowing them with what it calls FastStream64 technology. FastStream64 involves not just a highly efficient memory controller, but also a special setting for low-latency memory access with certain memory configs. The optimal config for FastStream64 is a single, dual-sided DIMM. With this setup, the PT800 performs especially well. FastStream64 also works nicely with a pair of single-sided DIMMs; performance should be within 1% of the single dual-sided DIMM configuration, according to VIA. Of course, if you add more DIMMs or use the wrong types, performance will likely drop off.

The PT800 north bridge chip gets a very healthy dose of active cooling

VIA recommended we test with a single dual-sided DIMM configuration, using a Corsair XMS3500 module, and in fact the reference board we were testing wouldn't operate properly with two DIMMs installed. We tested with VIA's recommended config, and our scores should provide a useful preview of PT800 performance. However, we will be eagerly anticipating production PT800 boards, so we can see how this chipset performs with other memory configurations.

The new south bridge chip: more marketing terms per
square millimeter than anything but a GPU

Once you get past the faster bus and the juiced-up memory controller, the PT800's new enhancements are all in VIA's new VT8237 south bridge chip. To get there, though, you'll have to traverse the upgraded V-Link interconnect between the north and south bridges. VIA's interconnect technology is back with a new name, Ultra V-Link, and it's now double-wide with 16-bits of bandwidth, for an effective throughput of just over 1GB per second.

That extra bandwidth will be helpful, because the VT8237 can host as many as eight hard drives off its Serial ATA and ATA/133 drive controllers. (This conglomeration of SATA and ATA/133 controllers has picked up a marketing name: DriveStation.) Like Intel's ICH5R south bridge, the VT8237 supports Serial ATA RAID, with both BIOS-based array creation and a Windows-based array management utility called DriveThru. VIA's official name for the VT8237's RAID capabilities is V-RAID, which seems appropriate and sounds vaguely like a newfangled weapon. Unlike Intel's south bridge-based RAID, V-RAID enables a range of RAID flavors, including RAID 0, 1, 0+1, and JBOD. The most exciting news here is RAID level 0+1, which uses four drives to achieve the ideal combination of increased performance via striping and data integrity via mirroring. RAID 0+1 is the hard-core PC freak's best path to storage nirvana.

In order to support four Serial ATA drives, VIA uses a unique combination of elements. The VT8237 supports two channels of Serial ATA natively, while offering an interface for two more channels with the help of an external physical layer interface chip from Silicon Image. To further the onslaught of marketing terms, VIA has dubbed this arrangement SATALite. SATALite is essentially a cost-effective means of extending V-RAID to allow four drives, and thus RAID 0+1, without ballooning the VT8237's transistor count. Motherboard manufacturers will have to decide to include this additional chip, but I expect many of them will. For the past year or so, many motherboard makers have used Silicon Image chips to convert ATA/133 channels on Highpoint PCI RAID chips into Serial ATA drive ports. SATALite is a clever, logical extension of this approach, made superior by virtue of its native SATA support and its location on the south bridge.

In short, V-RAID supports more RAID levels and twice as many SATA devices as the Intel ICH5R. However, the current iteration of V-RAID lacks the Intel ICH5R's slick ability to convert a single drive into a RAID 0 array within Windows completely on the fly.

A block diagram of the PT800 chipset. Source: VIA

Like its predecessor, the VT8237 includes six-channel AC97 audio output capability. Pair this capability up with VIA's own Six-TRAC codec chip, stir in the Stylus 3D audio driver technology licensed from Sensaura, and you've got Vinyl Audio, VIA's answer to similar solutions from Intel and NVIDIA. VIA is also pushing Vinyl Gold Audio, which bypasses the VT8237's audio capabilities entirely in favor of VIA's Envy24PT sound chip. Vinyl Gold, however, is essentially chipset-independent.