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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.

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.

With the iPhone 5's A6 CPU, Apple has taken a big step: gaining complete control over the processor implementations for its iPhone and iPad product lines. That change may put Apple ahead of archrival Samsung's processor development, also based on ARM chip technology. And it gives Apple the power to more fully control the complex tradeoffs of battery demand, CPU performance and graphics performance in the end user's computing experience.

Teardowns, such as the one by iFixit.com and Chipworks, and by UBM TechInsights confirm that the A6 uses two ARM-based but Apple-designed cores for the CPU, along with three integrated Imagination Technologies' PowerVR graphics cores. Apple seems to have systematically pieced together the elements to at least double the iPhone 5 performance over that of the iPhone 4S.

In a variety of benchmark tests, such as those by Anandtech.com, the CPU and graphics performance puts the iPhone at or near the top of the heap compared to high-end rivals such as the HTC One S or X, LG Optimus G and Samsung Galaxy S 3. The tests also show that the iPhone 5 compute and graphics performance is often comparable to, or better than, the new iPad, which runs the A5X chip.

The A5X and its earlier brethren are different from the A6 in one very important way. Until now, Apple licensed and used ARM's microprocessor core designs, along with the relevant software, for its mobile processors. This is the same approach used by many other companies, including Broadcom, Nvidia and Texas Instruments. All of them combine these cores with a variety of other components -- baseband chips, memory, graphics processors and so on -- to create their own system-on-chip (SoC) which gets plugged into the final assembly for a phone or tablet. This approach allows for a lot of innovation by the chip designers, who can combine different numbers of cores, or run them at different clockspeeds, for example.

But Apple is one of a much smaller group of companies (Qualcomm is another) that also has licensed the underlying ARM instruction set architecture (ISA), in this case ARMv7 which is widely used in other mobile products. With this instruction set "recipe," Apple's own chip designers can craft their own cores, and tailor them specifically to the company's mobile platform priorities. "You have absolute control over your [chip] roadmap and the features that are important to you," says James Bruce, lead mobile strategist with ARM. "It's not an exercise for the fainthearted. You probably need about 50 to 100 highly skilled engineers. And it's a multi-year project."

 

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