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NVIDIA's nForce 590 SLI
NVIDIA's nForce4 chipset family was introduced more than a year and a half ago, so it's long overdue for a replacement. The nForce4 SLI X16 refresh did little more than add PCI Express lanes via a discrete north bridge chip, leaving plenty of room for NVIDIA to break new ground with its nForce 500 family—and it has, expanding and refining features found in the original nForce4 while adding new bells and whistles along the way.

The nForce 590 SLI occupies the high end of the nForce 500 series, and as one might expect, it's capable of providing a pair of PCI Express graphics cards with 16 lanes of bandwidth each. Rather than consolidating those lanes in a single chipset component, NVIDIA splits them between the nForce 590 SLI's north and south bridge chips. This arrangement works well enough with the nForce4 SLI X16 chipset, perhaps in part because NVIDIA uses a 16-bit, 1 GHz HyperTransport chip-to-chip interconnect that offers a whopping 8 GB/s of bandwidth. That's as much bandwidth as the Athlon 64's HyperTransport link to the rest of the system, making it unlikely the nForce 590 SLI's chipset interconnect will become a bottleneck.

LinkBoost in action
Source: NVIDIA

Just in case that's not enough, the nForce 590 SLI also incorporates what NVIDIA calls LinkBoost technology. LinkBoost increases the clock speed of the chipset's interconnect and PCI Express graphics links by 25%, boosting the bandwidth available to each to 10 GB/s. NVIDIA is adamant that LinkBoost isn't overclocking—the chipset's PCI Express and interconnect links have all been tested and qualified up to 125% of their default speeds. There is one catch, though. Because LinkBoost increases the clock speed of the PCI Express bus, it requires a graphics card that can handle the extra speed. To date, the only graphics card that NVIDIA has deemed LinkBoost-compatible is the GeForce 7900 GTX.

LinkBoost is a neat trick, but with such restrictions, its potential benefits won't be universal. Those benefits may be few and far between, anyway, since the chipset's link to the CPU (and thus to main memory) tops out at 8 GB/s.

At least the nForce 590 SLI won't be bottlenecked when it comes to networking performance. The chipset's south bridge component has two Gigabit Ethernet MACs—one more than the nForce4 series. Each of those MACs has its own TCP/IP offload engine, promising lower CPU utilization during GigE transfers—for real this time, NVIDIA says. The nForce4 series apparently had a hardware bug that limited the TCP/IP offload engine's effectiveness, forcing NVIDIA to back off the chipset's hardware acceleration to avoid data corruption. According to NVIDIA, that bug's been fixed in the nForce 590 SLI, a claim we'll put to the test in our Ethernet performance tests.

NVIDIA has actually ditched the ActiveArmor moniker for the nForce 590 SLI's Gigabit Ethernet controllers, perhaps to avoid association with the CPU utilization and data corruption problems that dogged the nForce4 family. The nForce4's personal firewall software hasn't made the transition to the nForce 500 series, either. That creates interesting implications for hardware acceleration, because the nForce 590 SLI's TCP/IP offload engine isn't compatible with third-party firewall software. You can use the TCP/IP offload engine or you can run third-party firewall software, but not both together.

Without FirstPacket
Source: NVIDIA

NVIDIA has added a few new wrinkles to nForce 500 series networking. The most interesting new addition is a quality-of-service feature that NVIDIA calls FirstPacket. With FirstPacket, users can set higher priority levels for certain applications, allowing packets from those apps to cut in line and be transmitted ahead of packets from lower priority programs. Application priority is defined through an easy-to-navigate Windows driver control panel, making FirstPacket configuration a snap.

With FirstPacket
Source: NVIDIA

FirstPacket looks particularly promising for gamers looking for more consistent ping times while transferring files or running programs like BitTorrent in the background, but there are limitations. The nForce 590 SLI only has control over the packets it sends out, since it must accept every packet it receives. Therefore, FirstPacket is only capable of prioritizing outbound packets. That may be a significant limitation for folks who spend more time downloading than uploading, but NVIDIA only has control over the chipset, so they can't impose a quality-of-service scheme on other network clients.

In addition to FirstPacket, the nForce 590 SLI also sports an EtherChannel-like Gigabit Ethernet teaming feature dubbed DualNet. DualNet takes advantage of the nForce 590 SLI's pair of GigE MACs by combining them to act as a single networking controller. This double-wide Gigabit Ethernet connection can be used to push additional data. If one connection fails, the second will maintain service, adding a measure of fault tolerance. NVIDIA declined to reveal exactly how it presents the nForce 590 SLI's dual GigE controllers as a single unit, but admitted that the scheme involves "playing some games" with ARP spoofing, among other tricks.

DualNet's ability to boost networking throughput to a theoretical peak of 2 Gbps is an intriguing prospect, but one that few users will be capable of exploiting. It would take multiple GigE-capable clients to saturate a 2 Gbps connection, and even then, NVIDIA is only guaranteeing a 40% performance boost. That said, in a multi-client demo it showed the press, NVIDIA was able to leverage DualNet to boost networking throughput by 70%. Ultimately, DualNet's performance potential looks more appropriate for server and multi-user environments where the nForce 590 SLI will be rare at best. DualNet's fault tolerance also seems better suited to server environments. Perhaps we'll see it appear in NVIDIA's next-gen workstation and server chipsets.

However, for those who lack a Gigabit Network, DualNet is capable of teaming a pair of 10/100 Fast Ethernet connections. Home users could find that capability useful, especially at LAN parties where systems are often share a large number of files with multiple clients.