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  • Apple's A5: Two Cortex-A8s Under the Hood?


    The new A5 system-on-a-chip in the iPad 2 has been said to have a "dual-core" processor with "up to 2x" the power of its predecessor, the A4. However, if you review the actual words Steve Jobs used when announcing the new iPad, you'll note that he says "two processors inside" right after he reads "dual-core processors" off the slide. It's a meaningful distinction, because if "dual-core" meant a Cortex-A9 CPU, that would give the iPad 2 much more than "up to twice as fast on CPU performance." Given the low power draw of the new SoC, it's reasonable to speculate that what they've done is cram two low-power Cortex-A8s in there, rather than a single Cortex-A9.

    The graphics chip inside the A5 is widely assumed to be the PowerVR SGX543: with a render rate of 40 million polygons per second and a fillrate of 1 Gpixel/sec at 200MHz, this chip would certainly live up to the claim of "up to 9X faster graphics." However, all that extra processing draws power, and with battery life being held constant relative to the first-generation iPad, this would mean that power draw of the CPU has been dramatically reduced. A dual-core Cortex-A9 running in "power optimized" mode yields only 800 MHz, short of the 1 GHz claimed by Apple.

    Jobs claimed his "chip wizards" came up with the new A5 design, indicating that the team that was able to squeeze 67% faster clockspeed out of the iPhone 4 and iPad's single Cortex-A8 relative to the same chip in the iPhone 3GS may have been able to achieve the same feat with two A8s. The term "dual-core" usually refers to two processing cores on the same silicon die, but this is fairly loose terminology.

    What seems unquestionable is that Apple is going to route of pushing the speed and efficiency of ARM processors in its SoC designs, rather than going with off-the-shelf hardware. This gives a couple of advantage over the medium term. First, they can keep costs low by going with older chipsets rather than the latest-and-greatest technology. Secondly, when future SoCs do incorporate faster chips like the A9, they'll be able to squeeze more power out of them, and longer battery life than their competitors.

    Source: TiPB
    This article was originally published in forum thread: Apple's A5: Two Cortex-A8s Under the Hood? started by Paul Daniel Ash View original post