Apple is to buy a microprocessor design company founded by one of the key minds behind the ARM chip design that went on to become Intel's erstwhile XScale family.

The firm in question is PA Semi, which currently develops low-power processors based on the PowerPC architecture. Apple's dealt with PA before, as a possible supplier of advanced PowerPC chips for the old Power Mac and PowerBook lines. Ultimately, Apple went to Intel instead.

PA was founded by Dan Dobberpuhl, who had been lead designer of DEC's Alpha and StrongARM chips. Intel bought Alpha and StrongARM as part of a legal settlement struck between the two chip makers in the late 1990s, and rebranded the newly acquired chips 'XScale'. Dobberpuhl is PA's President and CEO.

Intel has since sold off its XScale product line to Marvell, part of its plan to focus on its x86 architecture, even into the very low-power applications it once targeted XScale at. The first fruit of that programme is the 'Silverthorne' Atom CPU formally announced earlier this month.

Silverthorne is aimed at internet tablets, and Atoms capable of powering phones aren't due until 2009-2010 when Intel is scheduled to launch the next major incarnation of Atom, 'Moorestown'.

It's been suggested that Apple will migrate its ARM-base iPhone to Atom when Moorestown becomes available, but the move to buy PA seems to suggest otherwise. Certainly having established the iPhone - and, indeed, the iPod - as ARM-based devices, it would be tricky for Apple to shift the platform over to a whole new, incompatible architecture so soon.

That said, it managed it twice with the Mac, and there are distinct development advantages of going x86, not least the fact that code developed for one version of Atom will run on any other - and, indeed, on regular desktop and laptop x86 CPUs.

Different generations of ARM processor, and versions from different manufacturers, are often incompatible at the binary level, forcing developers essentially to create entirely separate versions of their apps for each CPU they use in their hardware.

Apple has confirmed the bid to buy the closely owned PA, but it refused to comment on its reasons and plans for the acquisition. It's easy to assume Apple wants the company for its expertise, but it might simply see strong commercial value in PA's current product line and believes it could profit by allowing PA to continue as it has been.

Certainly, it's hard to see Apple embracing PA's Power-based 64-bit PWRficient processors per se, but PA's experience of developing low-power chippery could allow Apple to have a stake in future ARM developments.