There is nothing better than a new version of a technology that delivers tangible benefits over the old. We are massive fans of USB 3 here in the PC & Tech Authority Labs for that very reason – plug a USB 3 drive into a USB 3 port and you’ll have a very hard time going back to the slower speeds of USB 2.
This is because there were some pretty defined limitations with USB 2, enhanced by the general lack of adoption of eSATA in the market. Not only were external hard drives being choked down by USB 2 bandwidth, but the proliferation of cheapf lash memory meant that USB thumb drives were both dropping in price and climbing in performance.
Similar reasoning has gone into the introduction of PCI-Express Gen 3. While the most common use of PCI-Express is connecting discreet graphics cards, there is an emerging category of PCI-Express SSDs, much in the vein of OCZ’s RevoDrive series. Designed to get around the bandwidth limitations of Serial ATA, PCI-Express based SSDs are by far the fastest storage available to consumers.
Unlike graphics cards, which aren’t yet pushing the boundaries of PCI-Express Gen 2, SSDs can theoretically scale well beyond the current speeds. This was one of the driving forces behind the development of Gen 3, which is designed to set the groundwork for the next few years of PC hardware.
However, because most people immediately associate PCI-Express with graphics cards, there is an expectation that it is going to be needed for high end performance. The reality is that this isn’t the case – not only don’t graphics cards use all the bandwidth of the existing standard, but the slow upgrade cycle means that it will be years before there is enough of a commercial reason for game companies to develop with the higher bandwidth of PCI-Express Gen 3 in mind.
There are plenty of analogs for this – take NVIDIA’s PhysX technology for example. Despite the fact that it has now been around for years, developing a game with PhysX at its core isn’t viable because you automatically cull the owners of Intel and AMD GPUs from your game’s customer base. Design for PCI-Express Gen 3 and you basically exclude anyone who has bought a graphics card that predates the launch of the RADEON HD 7970.
HOW DOES IT WORK?
AMD's new RADEON HD 7970 card is the first PCI-E Gen 3 expansion card to hit the market..
Perhaps the most telling sign that PCI-E Gen 3 is playing the long game is the fact that AMD’s current enthusiast platform, the 990FX chipset, lacks support for the technology. At the moment the only GPU manufacturer doing Gen 3 is AMD itself. Put the two together and its clear that the one company that makes both ends of the PCI Express pipeline doesn’t see an urgency in getting the technology to market for GPU usage.
Intel, on the other hand, is midway through the introduction of Gen 3. Unlike AMD, which still includes the controller for x16 PCI-E graphics card lanes on the motherboard, Intel has moved control into the CPU itself. The current mainstream Core I ‘Sandy Bridge’ products have a PCI-E Gen 2 controller built in. The new enthusiast Sandy bridge-E Socket 2011 platform has a Gen 3 controller inside it, but at the time of launch Intel only quoted Gen2 support due to a lack of expansion cards with which to test and validate Gen 3.
Intel hasn’t announced the nitty gritty of PCI-E inside the upcoming Ivy Bridge refresh of its mainstream processors, but thanks to some aggressive motherboard marketing late last year it is a pretty sure bet that it will have a Gen 3 controller. One thing we do know about Ivy Bridge is that it will be socket compatible with the existing Z68 chipset, and most Z68motherboards are now using the correct chips to enable Gen 3 support.
In order to get Gen 3 working one needs three key parts. The controller, which in Intel’s case means the CPU. The second is a Gen 3 based expansion card, which for now means one of AMD’s high-end RADEON HD 7000 series products. The third is a motherboard that has both the BIOS and is wired the right way. The actual wiring on the motherboard isn’t the issue – rather it is the switches used to enable the use of dual graphics cards.
When running dual graphics cards the 16 PCI-E lanes built into a SandyBridge CPU need to be split into two x8 connections. This means that most motherboards are wired with eight lanes going direct to the main graphics slot, and a further eight lanes running through a set of small switches. When running a single card the switches just pass the traffic to the main slot, however when using two cards they redirect the eight lanes to a secondary slot. This means that these switches need to support the faster transfer speeds of Gen 3 when managing the connection – otherwise you would only get eight lanes of Gen 3 regardless of whether you have one or two GPUs.
Of course, eight lanes of Gen 3 workout to the same speed as 16 lanes of Gen 2 PCI-Express, so this is largely a marketing, rather than a user, issue. It is also a moot point now because the major motherboard makers have made the shift to the new switches. You can also be certain that when the official chipsets for Ivy Bridge arrive they’ll be packed onto motherboards that are fully capable of delivering a Gen 3 connection.
WHY YOU DON’T NEED TO WORRY
Intel’s Sandy Bridge-E CPUs and X79 chipset unofficially support PCI-E Gen 3.
One of the most frustrating things about deciphering the PCI-Express Gen3 workings is that Intel especially just isn’t talking about it. This is common practice for Intel – it doesn’t mind vague details of its next generation CPUs being talked about (just look at all the Ivy Bridge Ultrabook talk from CES), but it doesn’t like talking specifics until the CPUs are ready to hit stores.
What we can finally do with the launch of AMD’s RADEON HD 7970 is take a look at how Gen 3 is performing. Despite the fact Intel hasn’t officially supported PCI-E3 with Sandy Bridge-E, we now have motherboards with the appropriate UEFI settings to enable Gen 3. So we have run a few basic tests to see just whether there is any point making PCI-E 3 a priority when choosing hardware.
Our testing relies on components that are ultra high-end, which has the side benefit of reducing potential bottlenecking by the CPU or GPU. We have tested with an ASUS RAMPAGE IV Extreme X79 chipset motherboard, Intel Core i7 -3960X CPU and an ASUS RADEON HD 7970. One of the great things about the UEFI setup on the Rampage IV Extreme is that we have been able to switch between Gen 3, Gen 2and Gen 1 connections.
As you can see from the results in Crysis there is actually very little difference at all when switching between versions of PCI Express. This is largely down to the fact that even the most taxing games nowadays are CPU rather than GPU limited – effectively the game engine has ample GPU power available, and the overall speed is limited by how fast the CPU can do its share of the work. Not only is this the case with Crysis, but also widely-used game engines like Unreal. Look at the results and you’ll notice that even the Gen 1 connection delivers the same framerates at the Gen 3 one.
With this in mind we also tested with3DMark 11. This is a synthetic gaming benchmark, but as is often the case with artificial tests it puts a lot more stress on the communication between CPU and GPU than a real game would. We just ran the extreme test in order to stress the system, and the results paint an interesting picture.
You can see that the Gen 1 connection gets choked up and severely limits performance, delivering a score that is half that of the Gen 2.However the Gen 2 and Gen 3 scores are incredibly close to each other. Which brings us back to where we started. Current graphics cards don’t even max out PCI-Express Gen 2 bandwidth, and given that your average PC gamer is keeping the same hardware for longer and longer, we cannot see the massive bandwidth gains of PCI-Express Gen 3 being tapped by graphics cards for some time yet. When even the fastest GPU on the planet shows no difference in performance between Gen 2 and Gen 3,you can be safe in the knowledge that the transition to the new technology will come naturally as you upgrade or replace components, and that you wont be missing out on anything in the interim.
