Quad-Channel Memory And PCI Express 3.0
Quad-Channel Memory Control
All three models sport the same quad-channel memory controller officially rated for data rates as high as 1600 MT/s. That’s up to 51.2 GB/s of bandwidth, in theory.
Although we used Intel’s DX79SI motherboard for all of the performance benchmarking in this piece, the platform had a hard time scaling beyond DDR3-1600 using any of the quad-channel kits in our lab. So, I swapped into an Asus Rampage IV Extreme that arrived a little later, and used a set of G.Skill Ripjaws Z F3-17000CL9-4GBZH modules rated for DDR3-2133 to test scaling.
Jumping from DDR3-800 to -1066 to -1333 and then -1600 yields impressive throughput gains, reflected in some solid performance improvements (WinRAR) and other, less notable speed-ups (3ds Max).
For now, my recommendation is to grab the lowest-latency quad-channel DDR3-1600 kit for which you’re willing to pay. Thomas is already working on our first high-end memory round-up aimed specifically at X79, though, which promises to shed more light on the sensibility of the kits with gobs of headroom for overclocking.
PCI Express 3.0
Sandy Bridge-E’s memory capabilities are decidedly more relevant in the server space. However, the design’s PCI Express connectivity might appeal to power users with an affinity for multi-card graphics subsystems.
One of the most controversial points in my Sandy Bridge-E preview was the fact that PCI Express 3.0 was stated "not supported" by the manufacturer of my test platform. Multiple outside sources indicated that third-gen PCIe was planned, but wouldn’t be available, possibly until 2012.
It turns out that PCI Express 3.0 is, in fact, supported by Sandy Bridge-E (and the preview was updated to confirm 8 GT/s support the day after it went live). But because there weren’t (and still aren’t) any third-gen devices available yet, validating the feature was problematic. In fact, as you can see in the image below, Intel is still only officially guaranteeing that PCI Express 2.0 works, and probably will continue to do so until we see some hardware with a third-gen interface.
Nevertheless, Intel’s Core i7 datasheet confirms PCI Express 3.0 compliance, enabling up to 1 GB/s of bandwidth per lane, per direction.
Forty lanes of connectivity are built into all three Sandy Bridge-E-based processors, divisible into as many as 10 different ports. Most motherboard vendors will probably configure their platforms for three or four graphics cards, resulting in two x16 slots and one x8 slot, or one x16 link and a trio of x8 connectors.
Compared to Sandy Bridge and its 16 lanes of second-gen PCIe on each CPU, Sandy Bridge-E’s 40 lanes are downright decadent. But don’t expect that improvement alone to yield better gaming performance with multiple GPUs installed. After all, we’ve already proven that you can get exceptional performance from three graphics cards with a three-part series on the matter. At least until we’re able to test with PCI Express 3.0-capable devices, there’s no reason to demand the connectivity Sandy Bridge-E offers when an LGA 1155 platform equipped with Nvidia’s NF200 bridge isn’t even starved for throughput.
Where Sandy Bridge-E could positively impact gaming performance is with its enhanced processing power. Nvidia says the CPU’s speed-up is able to maximize scaling with three of its GeForce cards installed, and we’ll be testing that claim shortly. PCI Express isn’t credited with the improvement, though. The six Sandy Bridge cores and big L3 cache get that honor.