Apple’s MacBook Air is a great piece of kit in a number of scenarios, but if you’re a gamer, it’s not a great system. The only available graphics option is the Intel HD 5000, and while that core is decent enough for the casual gamer, it’s still weak compared to other solutions for any modern title. In theory, Thunderbolt is capable of fixing this; the standard offers direct GPU attach capability via the PCI-Express bus and connects to the motherboard on an x4 PCIe 2.0 link. In practice, however, Intel has refused to certify any direct GPU solutions. While we’ve seen several manufacturers demo such products, no one has shipped an external GPU chassis yet.
Fed up with this state of affairs, TechInferno.com forum member Kloper decided to build his own. On the hardware side of the equation, that meant buying an adapter for converting PCIe video cards to ExpressCard slots. The PE4L-C060A from Bplus Technology is capable of handling this task. Next came an Express Card to Thunderbolt chassis courtesy of Sonnet ExpressCard Pro. Run the Thunderbolt cable from the ExpressCard Pro converter to the laptop, hook the GPU up to a power supply, and the hardware side of the equation is good to go.
Software-side, there are still some kinks. You’ll need the DIY eGPU Setup 1.x software to make the entire process work smoothly. Kloper attributes the functionality to DIY eGPU creator nando4, but the “purchase” page for the product appears to currently be down. It’s not clear from this description exactly what the product does, but it avoids the “Error 12: Cannot allocate resources in Device Manager” problem that apparently hits some systems, including the MacBook Air. According to Kloper, AMD and NV GPUs are both supported, but AMD GPUs will need to use Intel/Lucid’s Virtu software under Windows 7 in order to get the device up and running.
As you might expect, the final setup, though technically beautiful, has some issues. You’ll have to reset the GPU by cycling the power supply if you reboot the system, and the enclosure/cabling can kindly be called messy. But the results, according to both these tests and other articles around the ‘net, are impressive. Games are four or five times faster on the MacBook Air’s LCD, and five to seven times faster on a separate external monitor. Kloper calls this “eminently practical,” which I’m not sure I agree with given the additional $ 300 cost (not counting the GPU itself), the difficulty, and the rather tortured connection system required to make it all work — but it is impressive.
Gaming on a single-channel — what’s the performance hit?
One interesting question is just how much of a performance hit games take when you run them through this kind of system. In theory, Thunderbolt can provide up to four PCIe 2.0 links, since that’s the width of the channel that connects the controller to the motherboard. The PCIe 2.0 to ExpressCard link, however, is just x1. The card is open-ended, which allows for anything up to an x16 card, but it’s only providing one channel worth of bandwidth. That’s about 400MB in either direction once we account for transmission overhead.
Interestingly enough, AMD and NV cards don’t exhibit the same behavior here; test results indicate that Nvidia’s GeForce GTX 680 loses 33% of its performance on a PCIe 1.1 x4 link, while the AMD Radeon HD 7970 only drops by 17%. Keep in mind, however, that PCIe 1.1 x4 is still capable of an 800MB/sec effective transfer rate — double what we see here. The implication is that the PCIe 2.0 x1 link will hit performance harder than this. Exactly how hard will depend on the game, but it’s safe to assume an external desktop GPU will only offer 65-80% of theoretical full performance when connected in this fashion.
Up until now, laptop docks with external GPUs have been more an idle curiosity than a feasible product, but if mobile products continue to surge, they might become more popular. The ability to tap an external GPU over a high-speed connection could become a distinguishing feature of laptops over tablets, and it’s an option that would appeal to professionals who want light laptops for traveling but need high performance at home or work.
Absent major shifts in consumer uptake, laptop docks of this sort may remain a niche product, but clearly there’s enough interest that some people are rolling their own solutions. Kloper’s design is cool, but there’s a definite latency cost associated with switching PCIe 2.0 to ExpressCard to Thunderbolt. Just pairing directly to the Thunderbolt controller would improve the situation, while linking directly to TB and simultaneously boosting bandwidth to even PCIe 2.0 x8 would likely kill the penalty altogether. Intel, are you listening?