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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.

And Apple has such a team. In April 2008, Apple acquired semiconductor design firm PA Semi for $278 million. "That acquisition included a CPU design team that had developed a high-performance PowerPC processor under the leadership of Jim Keller and Pete Bannon," notes a recent blog post by Linley Gwennap, principal analyst for The Linley Group, a technology analysis firm focused on semiconductors. "More important, some of the team members had previously worked on low-power StrongArm processors under PA Semi CEO Dan Dobberpuhl at Digital Equipment (DEC) in the 1990s."

Shortly after that purchase, Apple secretly signed the architecture license with ARM. One team began working on the A4, using licensed ARM core designs, but another team "began defining the microarchitecture for the new CPU," according to Linley. The design was finished by early 2010, and Apple then launched the physical design work. About the same time, Apple hired as its chief CPU architect Gerard Williams from ARM, where he was the technical lead for the Cortex-A8 and Cortex-A15 CPUs, according to Linley. And shortly after, Apple made its second silicon-related acquisition: paying $120 million in April 2010 for Intrinsity, with expertise in high-speed physical design.

This expertise now puts Apple on a sustainable evolution in processor design, tailored to its specific needs.

"Mobile processors have been using Cortex-A9 [core designs] for the past two-plus years," Linley says in an email. "Cortex-A15 is the next step in ARM's roadmap, and the first Cortex-A15 should appear in phones around the end of this year. It offers a large increase in performance, although at some cost to battery life."

But it's also designed to meet requirements for a very wide range of end products, from smartphones to big servers. Apple will forgo ARM's A15 designs but create an A15-class CPU of its own specifically for mobile devices. "Having control of the CPU allows Apple to optimize the design to meet its own needs," Linley says. "Apple is willing to spend a little more money -- on a more expensive CPU -- if it makes the end product, such as an iPhone, noticeably better."

According to a battery of initial tests by Anandtech.com, Apple has done exactly that with its first custom CPU, running the iPhone 5.

"Overall, the performance of the A6 CPU cores seems to be very good," writes Anand Lal Shimpi. "Apple claimed a 2x CPU performance advantage compared to the iPhone 4S during the launch event for the 5. How does that claim match up with our numbers? Pretty good actually. ... This is hardly the most comprehensive list of CPU benchmarks, but on average we're seeing the iPhone 5 deliver 2.13 times the scores of the iPhone 4S."

 

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