A thesis called Porting Darwin to the MV88F6281 describes how Apple’s Platform Technologies Group spent time in 2010 working on porting Mac OS X to ARM processors and was written by Tristan Schaap, who was at the time an intern but now works full time for Apple as a Core OS engineer.
Published by the Delfte University of Technology and picked up by the iMore blog, the paper details how Darwin – described by Schaap as “the lower half of the Mac OSX operating system” and including the XNU kernel, which is based on the Mach microkernel, and the userland – could be got into a workable state on the MV88F6281 processor.
The MV88F6281 is described by Schapp as “an ARMv5te compatible processor from Marvell. It is based on their custom Sheeva core, which is designed to be like the ARM926EJ-S core from ARM”.
The paper’s existence would seem to suggest that Apple has considered the possibility of a MacBook Air or perhaps even an iPad or iPhone running OS X.
Of course, the company did used to run Mac OS X on Power PC chips before moving to Intel and presumably had done extensive work on the possibilities of doing so beforehand. As iMore’s Jack Perry points out: “It only makes sense for a company as forward thinking as Apple to have ARM-compatible builds of OS X in the development labs.”