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First Sightings of SATA 6Gbit/s and USB 3.0

First Sightings of SATA 6Gbit/s and USB 3.0

By now, most of you would have heard all about the next-gen storage interface, SATA 6Gbit/s and the ubiquitous USB 3.0. SATA 6Gbit/s, as its numbers would indicate is exactly twice that of the existing SATA 3.0Gbps specifications. Already, we have seen the first SATA 6Gbit/s hard drive available from Seagate (Barracuda XT) and more will be released next year as solid state drives are quickly hitting the limits of SATA 3.0Gbps. USB 3.0 meanwhile, extends the maximum transfer rate of the current version 2.0 by up to 10 times. Crucially, it is backwards compatible, so a new USB 3.0 device would degrade to the slower standard if the other party (host) is only USB 2.0 compatible.

They both sound like significant additions to the technology, especially USB which is so popular among users. Portable storage for instance would benefit greatly from the increased data transfer rate. Unfortunately, there's a potential hitch in plans. Intel has delayed plans to integrate USB 3.0 in its chipsets to 2011; its current mainstream P55 chipset has already launched with a disappointing lack of support despite initial plans.

While we believe SATA 6Gbps will be more quickly adopted than USB 3.0, the fact is that current chipsets do not have support for either. This is where motherboard vendors and third-party vendors come into the picture. With no official chipset support, it's an opportunity for vendors to appeal to the early adopters and power users by including these new technologies. ASUS and Gigabyte are two such motherboard brands that have such products out now (you can get them from the usual retail channels) in their revised P55 motherboards.

Today, we'll be taking a look at these two motherboards, the ASUS P7P55D-E Premium, based on the original P7P55D Premium and the Gigabyte GA-P55A-UD6, which is a revised Gigabyte P55-UD6. These boards are based on existing models but enhanced with these new features. As for the performance of these boards when it comes to SATA 6Gbit/s and USB 3.0, we'll be covering them separately in the near future.

The Thing about SATA 6Gbit/s and USB 3.0

Before we move to the usual motherboard tests, there is however a difference in approach in implementation between the two vendors, ASUS and Gigabyte that we need to highlight. Since these features are not found in current chipsets, both companies rely on third-party controllers. For SATA 6Gbit/s, this controller is from Marvell while the USB 3.0 controller is manufactured by NEC.

These controllers are embedded on the motherboard, though other motherboard vendors may ship with add-on cards instead. ASUS is taking this latter route to add support for these features for the more affordable models in its line-up while Gigabyte will be releasing 'A' versions of all its P55 motherboards, like the P55A-UD6 that will come with SATA 6Gbit/s and USB 3.0.

One note about the controllers is that both ASUS and Gigabyte are using different Marvell controllers, with Gigabyte going for the 9128 chip that comes with an onboard micro-processor to reduce CPU utilization and also enable SATA RAID 0 support. ASUS chose the no-frills 9123 chip which just provides the basic SATA 6Gbps feature. Both vendors however use the same USB 3.0 controller model from NEC.

What's crucially is how the new features are implemented on the P55 chipset. As you may know, the Lynnfield Core i7/i5 processor integrates the PCIe 2.0 controller with 16 lanes into its CPU die. There is no PCIe 2.0 functionality on the P55 chipset by itself. This is fine for a mainstream platform since dual SLI or CrossFireX can be executed by having the graphics cards in dual mode with 8 lanes each. 3-way CrossFireX or SLI is another issue that requires some compromise and switching of PCIe 1.1 lanes available from the chipset.

This limitation of the chipset poses a problem for the SATA 6Gbps and USB 3.0 controllers. They each require the full 500MB/s bandwidth from a single PCIe 2.0 lane to reach their maximum speeds. If these controllers are connected to the P55 chipset, they can only do so via the chipset's PCIe 1.1 lanes, which are capped at 250MB/s per lane. It's either that or connecting these controllers to the processor's PCIe 2.0 lanes, which will then affect the reserved graphics bandwidth.

This approach of tapping into the PCIe 2.0 lanes is exactly what Gigabyte did with its P55A-UD6. As it states in red on its product page online, the SATA and USB functionality will revert to the normal SATA 3.0Gbps and USB 2.0 if you have installed two graphics cards on the board in SLI or CrossFireX configuration so as not to affect the graphics bandwidth. In short, this is not the ideal board if you plan to have dual graphics cards along with the expectations of using SATA 6Gbit/s and USB 3.0.

ASUS meanwhile uses a bridge chip on the P7P55D-E Premium to enable what it calls 'true' SATA 6Gbit/s and USB 3.0. What this bridge chip does is to convert four PCIe 1.1 lanes on the chipset to a bandwidth equivalent of a pair of PCIe 2.0 lanes. These can be used by the new SATA and USB controllers for the full bandwidth. Of course, this is still a compromise and technically not perfect, since these lanes have to come from somewhere but chances are, users are probably not too concerned about the loss of their PCIe 1.1 slots for example or the lanes from the Gigabit LAN (since there are two LAN controllers on the ASUS). The bridge chip however is additional cost that may be reflected in ASUS' pricing.

So, there you have it, the difference in implementation between the two boards featured here. We'll have to give the advantage to ASUS here since not having the full bandwidth for SATA 6Gbps and USB 3.0 when using CrossFireX or SLI is not what an early adopter or power user would have signed up for.