Also, most apps today are 32-bit, and they'll need to be rewritten to take advantage of the 64-bit capabilities. ARMv8 is backward compatible with its 32-bit predecessors, so existing apps should perform fine on the new devices.
Despite Apple's assurances, its effect on battery life could also be a concern. A 32-bit processor has been adequate thus far for mobile devices, and the burst in performance and memory addressability can only mean increased power consumption, Tirias Research's McGregor said.
Still, there may be other advantages. ARM's ARMv8 architecture has full virtualization support, which could eventually be used to run a guest OS on the iPhone, or even to run server-side apps locally to boost performance. It could also be used as a sandbox, to run potentially risky code in a secure environment.
The A7 will likely be used in the iPad as well as the iPhone, and could even find its way into MacBooks, which currently use Intel 64-bit Core processors. The ARM-based A7 could potentially provide the Macbook Air with longer battery life, for example.
"If they wanted to take this A7 chip and use it to build a MacBook based on ARM rather than Intel, they could conceivably do that," Brookwood said.
That would allow Apple to bring iOS and Mac OS closer together.
Ultimately, the bulk of the smartphone market is expected to move to 64-bit chips, and Apple's move positions it for the future.
"It's a good way to get people started on 64-bit; it doesn't hurt," Brookwood said.