Back at Computex 2011, MSI proudly pointed out that one of its motherboards, the Z68A-GD80 (G3), supported PCI-Express 3.0. Then last Friday ASROCK dropped by our offices and gave us a glimpse at an engineering sample of its upcoming high end Z68 Extreme7 Gen3 board. Nestled among the distinctive gold capacitors on this board were a couple of tiny NXP chips, which add PCI-E 3.0 support to the motherboard.
Then Friday afternoon ended with an announcement from Gigabyte of its new gaming board, the Z68 based G1.Sniper 2. We’d seen this board when it was tagged Z68-Gaming back at Computex, but Gigabyte had held one thing back in its early descriptions of the product – support for PCI-Express 3.0.
Seeing as three out of the four main motherboard manufacturers are supporting PCI-Express 3.0 it seemed high time to have a look at what the benefits are. After some digging and chatting with industry figures it might surprise you to know that the current benefits of PCI-Express 3.0 are absolutely zero. In fact, if you pair one of these boards with their intended ‘Sandy Bridge’ second gen Core CPUs you won’t ever have PCI-Express 3.0 running.
The reason behind this is that, thanks to the move of traditional chipset features onto modern CPUs, the all-important high bandwidth PCI-Express graphics lanes tie directly into the CPU. There are PCI-Express lanes that run into the Z68 chipset on the motherboard, but these are used for lesser means, where bandwidth isn’t critical. These are devices like networking controllers, PCI-E SSDs and the like.
In a Z68 chipset for example, there are eight PCI-Express lanes available. Some of these get used by the motherboard to attach USB 3 or SATA 6GBps controller chips, while others drive the smaller PCI-E connectors on the motherboard. A Sandy Bridge CPU controls a further 16 lanes, which can operate one graphics card at full x16 speed or two cards at x8 speeds.
This allows the best possible communication between GPU and CPU but it also means that the PCI-Express connection is inexorably tied to the CPU. This means that, despite the fact motherboards are now shipping with PCI-E 3.0 support, we won’t actually see any of these slots running at PCI-E 3.0 speeds until the launch of Intel’s ‘Ivy Bridge’ CPUs next year.
Even then PCI-E 3.0 will only come into its own when graphics cards support it as well. Once you have both CPU and graphics card support you’ll be able to tap into the effectively doubled bandwidth of the latest PCI-Express specification, but for now support is only there as a future proofing attempt by motherboard manufacturers.
In other words, it is nice to have, but would only be considered an essential buy if you planned to upgrade your CPU when Ivy Bridge and the new generation graphics hardware hits the market sometime next year. Because Ivy Bridge is the 22nm process shrink of Sandy Bridge and not a new architecture, one doubts that there will be the kind of huge performance jump that would make upgrading from the current range of Intel Core CPUs worthwhile.
