updated 01:43 pm EDT, Sun September 16, 2012
Anandtech reports other ARM processor families unlikely
The processor inside the new iPhone is neither an A15 or A9, as previously guessed, but is probably a custom Apple-designed processor. According to technical enthusiast website Anandtech, based on deduction and information given prior to the iPhone's announcement, the A6 processor in the phone "is the first Apple SoC (system on a chip) to use its own ARMv7 based processor design."
The author reports that given the iPhone 5 will ship with and only run iOS 6.0, and Xcode 4.5 has made major changes to support for ARM integrated developer environments (IDE) and application compilation, namely, the support of the VFPv4 floating point processor unit. The VFPv4 is only found in Cortex A5, A7 and A15 chips, and not in one likely suspect for the phone, the A9.
Given Apple's claims of twice the performance, the Cortex A5 and A7 chips are easily dismissible as the processor installed, leaving the A15 or some other sort of processor. Also, given the VFPv4 implementation, and Apple's claims of extended battery life with what is essentially the same battery in the new phone, Anandtech claims that an upclocked older processor isn't possible, as the enhanced battery life would require architectural differences not found in the older processor lines.
According to Anandtech "for unpublishable reasons, I knew the (Apple) A6 SoC wasn't based on ARM's Cortex A9, but I immediately assumed that the only other option was the Cortex A15. I foolishly cast aside the other major possibility: an Apple developed ARMv7 processor core." They add that "based on a lot of digging over the past couple of days, and conversations with the right people, I've confirmed that Apple's A6 SoC is based on Apple's own ARM based CPU core and not the Cortex A15."
The author does admit that "I have no details on the design of Apple's custom core" and posits that an A15/Krait class CPU as a reference design is possible with its expected architectural improvements. Apple is notoriously secretive about hard specifications on its processors before a device is in the hands of consumers, so even the core count on the processor is not known at this time in much the same way that the current-generation iPad's core count wasn't initially known. [via Anandtech]