AMD-powered MacBook Air, a tantalizing might-have-been

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It’s standard operating procedure for major OEMs to keep hardware on hand from a number of suppliers — Dell, for example, readily admitted to testing AMD CPUs for years before it actually offered any for sale. It’s therefore unsurprising to hear that Apple gave AMD’s Llano a test drive as a potential MacBook Air solution — but apparently Sunnyvale came much closer to winning Apple’s business than anyone might think.

According to SemiAccurate, Apple had a Llano-based design it intended to mass produce. AMD, however, was unable to guarantee a sufficiently large supply of processors due to ongoing yield problems at GlobalFoundries. Those issues have not yet been resolved. GloFo’s yields have steadily improved throughout 2011, but AMD’s volumes are still supply constrained.

In retrospect, Apple’s decision to go with Sandy Bridge over Llano was almost certainly the right one. Even if Sunnyvale could’ve met Apple’s product needs, it probably couldn’t have done so without shafting everyone else in the process. We’ve already heard rumors that the company’s OEM customers are unhappy with its ability meet previous product commitments, and it wouldn’t have been wise for Sunnyvale to burn all its bridges in favor of throwing in with Apple.

There’s another possible reason Apple may not have wanted to go the AMD route, though it hasn’t gotten much attention. There haven’t been many reviews on AMD’s new, Bulldozer-derived quad-core FX-4100 part — and for good reason. As LegitReviews demonstrates, the 3.6GHz FX-4100 CPU’s performance is terrible when compared against existing A6 and A8 Llanos. Bulldozer chips take a natural 15-20 percent performance penalty compared to previous AMD processors, and the FX-4100 only has a 100MHz Turbo Core envelope. As a result, the 3.6GHz FX-4100 is regularly matched by the 2.6GHz A6-3650 and soundly beaten by the 3.7GHz Phenom II X4 980 BE.

This has serious implications for Trinity, particularly since AMD can’t lean on a high-TDP Turbo Core frequency when building mobile parts. The existing FX-4100 draws less power than the X4 980 BE, but not nearly enough to compensate for its dramatically weaker performance.

Compare the FX-4100′s numbers against AMD’s published expectations for the future of BD processors and it’s clear that just matching Llano’s performance per watt will be a major accomplishment by the time Trinity rolls around. Everything we’ve heard thus far regarding Trinity suggests that the GPU and CPU-GPU interconnect will both be significantly improved, and as a result, AMD may be able to get by with holding CPU performance essentially static — particularly given how much of an improvement Trinity would be over Bulldozer just to hit such targets.

Two out of three, as the saying goes, ain’t bad. It’s probably enough to maintain AMD’s graphics performance advantage over Ivy Bridge. But it’s not surprising that Apple, who undoubtedly got a full preview of both Bulldozer and Trinity, would choose to go elsewhere.

From  http://www.extremetech.com