Why Apple rejected AMD’s Llano in the MacBook Air

Apple’s MacBook Air may have come close to shipping with AMD’s “Llano” integrated CPU and GPU processors this past summer. According to unnamed sources speaking to SemiAccurate, Apple had Llano-based MacBook Air prototypes “on the verge of production” but ultimately decided on Intel’s ultra-low voltage Sandy Bridge processors instead. Assuming it’s true that Apple was tinkering with Llano processors in its popular ultraportables—and we think it is—it’s worth considering why the company ultimately sided with Intel over AMD.

First, it should be no surprise that Apple experiments with processors from other sources besides Intel. It just makes good engineering and business sense to consider and test alternatives. Apple even reportedly has MacBook Air prototypes with ARM-based processors somewhere inside its Cupertino headquarters, so the fact that an alternate x86 prototype exists is really no revelation.

What may be surprising is that a MacBook Air based on Llano was apparently Apple’s “plan A,” according to SemiAccurate’s sources. However, that plan was allegedly scrapped sometime in the spring due to AMD’s inability to ship processors in volume. “Binned lower voltage premium versions are probably… rare enough that Apple would probably have been severely constrained on supply,” SemiAccurate wrote.

That’s no doubt an important reason for Apple to take a pass on Llano, but it’s certainly not the only reason. Early benchmarks revealed that Llano was a champ at keeping power use down—certainly a quality that Apple wanted for the Air. Llano also offers GPU performance that easily spanks Intel’s integrated HD3000. But Llano’s CPU performance doesn’t compare to Sandy Bridge, and its GPU is hampered by a lack of direct access to high-speed RAM.

Assuming AMD could have delivered on the quantities that Apple expected, Apple would have been stuck with so-so CPU performance and decent GPU performance. That is, in fact, the same basic compromise Apple made for the 2010 MacBook Air, pairing older Core 2 Duo CPUs with NVIDIA’s GeForce 320M controller with integrated GPU.

While that package, combined with a reasonably fast SSD, made for an overall useful machine, lackluster CPU performance was its top criticism. Sticking with AMD would have left Apple in the exact same position: great graphics, so-so overall performance. Gamers may have been happy, but then again, how many gamers are buying MacBook Airs?

Instead, Apple opted for Intel’s Sandy Bridge processors. The integrated HD3000 GPU is no powerhouse—in gaming performance, in particular, it’s actually not quite as good as the GPU in the NVIDIA 320M. But for the majority of tasks, graphics performance stayed steady while CPU performance crept up several notches. Essentially, the move made the MacBook Air a great machine for general use, decent for mobile media and content creation, and barely useable for high-end gaming.

Sticking with Intel also means Apple is ready to benefit from the chipmaker’s next-generation Ivy Bridge processors slated for next year. Ivy Bridge will combine several GPU improvements, including OpenCL compatibility and updated OpenGL support, with Intel’s highly efficient 22nm tri-gate transistor design. This will allow Apple to both improve performance while cutting power drain and likely increasing the MacBook Air’s already impressive battery life.

In the end, the choice Apple made looks like the right one. The MacBook Air now accounts for nearly one-third of Apple’s notebook sales, and Intel has spurred Windows PC vendors to create their own MacBook Air clones (with limited success, so far). AMD may be able to improve on Llano’s performance with some design tweaks, and its GPU performance will handily beat Intel’s, but for the time being it will remain a step or two behind Intel in terms of CPU performance. Having moved forward in that regard with Sandy Bridge, we don’t expect Apple to go back anytime soon.