Why Apple is unlikely to switch iOS to Intel processors
Rumors that Apple will port iOS to the x86 are abetted by the steady improvement of Intel's Atom-based chips for smartphones and tablets. Keep in mind that Intel and ARM started from opposite ends of the spectrum: Intel from high performance, ARM from low power. Now each company is moving toward the other's position and have nearly met in the middle.
Intel's Atom processor, introduced in 2008, was the company's first attempt to drastically reduce x86 power consumption. Initial Atom chips were great for netbooks but still way too hot for smaller devices like smartphones. In 2010, Intel's "Lincroft" processor (officially, the Atom Z600 series) moved graphics, video coding, DRAM control, display control, and I/O interfaces onto the same chip as the Atom CPU core. For Intel, this was a big step in chip integration and power efficiency, but "Lincroft" still ran relatively hot and required a companion chip to match the functions of competing single-chip processors.
In 2012, Intel introduced "Medfield" (officially, the Atom Z2460). This chip finally integrated the critical smartphone application functions on a single chip and cut power consumption to competitive levels. Even so, it's not quite good enough to convince most smartphone vendors to rewrite their ARM software for the x86. In fact, Intel has had to take on the work of porting Android to Atom; despite that effort, very few smartphones or tablets use it -- even though most Android apps are written in Java, which bridges chip platforms more easily than natively compiled code.
The next generation could tilt the balance in Atom's favor by fully exploiting Intel's manufacturing advantage. Up to now, Atom chips have lagged behind the company's PC and server processors. Whereas Intel manufactures its leading PC and server chips in the latest 22nm FinFET process, "Medfield" gets by with the previous-generation 32nm planar process.
From a business standpoint, this strategy makes sense, because PC and server processors sell at higher prices and in higher volumes. Future Atom chips, however, will no longer be hand-me-downs. Atom chips are moving to 22nm technology this year and to next-generation 14nm technology in 2014. ARM manufacturers simply can't match that pace.
But even if Atom can beat ARM's power/performance efficiency, Apple may not switch iOS to the x86. All those zillions of apps for iPhones and iPads are natively compiled for ARM. Either software developers would have to recompile them for the x86 or Apple would have to provide an ARM-on-x86 emulator. Although Apple has successfully used emulation to smooth the Mac's platform transitions, an emulator's overhead in CPU clock cycles, memory, and power would be a greater burden for a mobile device. Unless an Atom processor can emulate ARM faster than an ARM processor can run its own native code, Apple would have little or no technical reason to switch CPU architectures.