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iPhone 5 shows an Apple first: custom CPU core design

John Cox | Oct. 1, 2012
More details of the iPhone 5 CPU emerged this week, confirming Apple's claimed performance gains. But more importantly, they are the first indications of the impact of Apple's custom chip design, rather than relying on standardized cores licensed from ARM.

Part of the gain is realized by moving to a smaller die process for the chip, to 32 nanometers from 45 nm. But by itself that's not enough, according to Lal Shimpi.

Among his findings:

+ "The memory interface on the A6 seems tangibly better than any previous ARM based design, and the advantage here even outpaces Intel's own Medfield SoC."

+ In a pair of Google Javascript benchmarks, "we see huge gains over the iPhone 4S, but much closer performance to the [high-end] HTC One X [smartphone]."

+ "The A6 ... features a three core PowerVR SGX 543MP3 [graphics processor], running at higher clock speeds to deliver a good balance of die size while still delivering on Apple's 2x GPU performance claim."

+ "The result is compute performance that's similar to the A5X in Apple's 3rd generation iPad, but with a smaller overall die area."

+ "As we've seen in the past, these gains don't typically translate into dramatically higher frame rates in games, but games with better visual quality instead."

The iPhone 5 ranks at or near the top in these benchmarks, compared with an array of high-end rivals. Lal Shimpi noted that Qualcomm's ARM-based Snapdragon S4 Pro CPU with Adreno 320 GPU puts LG's Optimus G "hot on the heels of the new iPhone."

Why not just run the Cortex-A9 cores found in the earlier Apple A5 SoC at a higher frequency?

"To push frequency you have to push voltage, which has an exponential impact on power consumption," according to another post by Lal Shimpi. "Running your cores as close as possible to their minimum voltage is ideal for battery life. The right approach to scaling CPU performance is a combination of increasing architectural efficiency ([the number of] instructions executed per clock goes up), multithreading and conservative frequency scaling."

With full control of its CPU design, Apple now can exploit these kinds of synergies.

And that's one reason why Apple hasn't rushed into quad-core CPU designs for the iPhone. A range of tech blogs and news sites argued last year and this year that quad-core CPUs were needed to "compete" with Android smartphones that were making use of these powerful processors, such as the LG Optimus 4X HD and HTC One X.

"The problem with quad-core today is that apps must be modified to use all four cores," says Linley. "Few Android apps, for example, can do that, so Apple is not at a big disadvantage by having a dual core. By mid-2013, however, quad-core Android apps will be common, as will quad-core Android phones, so I think it would be a good time for Apple to follow suit."

 

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