Sunday, October 23, 2011

ARM's New Cortex A15 CPU: Destined For Macbook Air?

Jon Stokes, formerly of Ars Technica, has a new article up: Meet ARM’s Cortex A15: The Future of the iPad, and Possibly the Macbook Air. It's a typical Jon Stokes article about CPU architecture - and that's a good thing. Lots of talk about pipeline depths and so forth. His conclusion, based on "paper" evaluations of the A15 and Intel's upcoming products, is that the A15 is going to be great but it won't be compelling enough for Apple to consider switching some of their notebooks to that architecture.

Why RISC? The question of a switch to an ARM-based RISC architecture for Macs is tantalizing. The short version of a long story is that, all other things being equal, RISC architectures are always going to offer more performance-per-watt than CISC architectures like Intel and AMD's x86 chips. That's why you don't see x86 chips in cellphones and you very rarely see them in consumer electronics.

Why Didn't RISC Win The First Time? In the 80s and 90s, everybody was going RISC - except Intel, who needed to keep their desktop x86 CPUs backwards-compatible. Intel was able to defeat RISC desktop chips like PowerPC with their economic might. Even though their x86 chips needed more transistors and more power to match RISC competitors, Intel's massive profits, economies of scale, and industry-best chip manufacturing processes allowed them to maintain a performance lead and sell those x86 more cheaply than their RISC competition.

Why Might ARM Win This Time? The increased power consumption of Intel CPUs is no big deal on the desktop, where a few extra watts don't matter much. But with everything going mobile, it matters again. And unlike Microsoft, Apple already has an operating system that's poised to run on multiple architectures.

So it's a little disappointing to read that Stokes doesn't feel ARM's latest CPUs are enough to start nibbling away at Intel's presence in mainstream notebooks. The thought of dropping the "CISC tax" is awfully appealing.

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