One of the more impressive specs on the iPad is that Apple managed to get 10 hours of battery life on a device with a sizeable 9.7-inch screen. The processor behind this incredible achievement is the Apple A4, a system on a chip running at 1 Ghz and based on the ARM Cortex A9 CPU.
In 2008, Apple purchased PA Semi, a fabless semiconductor company known for churning out powerful processors that utilized relatively little power. Indeed, rumblings seem to suggest that the A4 was built by Samsung and designed by the PA Semi team acquired back in ’08. But what is it about the A4, exactly, that makes it so goddamn efficient?
To answer that question, Paul Boutin of Venture Beat put his ear to the ground, gathered up information from a slew of engineers (some of whom used to work at Apple), and even got a few “insidery sources” to chime in. According to Boutin, this is the best explanation he received regarding the iPad’s remarkable battery life.
PA Semi achieved something to write home about just as Apple defected to Intel: a 65nm 2Ghz, dual powerpc core processor that maxed out at 25 watts. That was supposedly tantamount to witchcraft, and an explanation I’ve seen for it was that PA Semi was able to break it up into a large number of smaller ‘power domains’ (if that was the term..), allowing them to keep more of the chip either at lower frequency or turned off completely. I also recall reading that this was extremely difficult.
The A4 story, really being whether it has much of an advantage over arm + graphics + … chips of the same generation (whether A8 or A9), hinges on whether Apple’s PA Semi talent and IP worked all that much magic compared to what e.g. TI or Qualcomm already achieved. That’s probably THE question to ask your Apple sources: how much PA Semi is in there, and how much better is that? They were previously the best of the best, does it still show in this new context?