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How did Apple arrive at the A6 chip in the iPhone 5? A longtime chip analyst documents the long and winding road.

While endorsing a report that the A6 is a unique Apple design, Linley Gwennap, who heads The Linley Group, a chip consultancy, posted a brief history of the A6's chip estimated $500-million-plus development effort in a research note on Saturday.

Some of the history has been documented before, but other parts are not as well known.

Gwennap's firm is the publisher of the Microprocessor Report and it frequently holds conferences on mobile chips.

Here are some of the highlights of Gwennap's post:



StrongARM: Apple's interest doing its own central processing unit (CPU) design dates back to its $278 million acquisition of PA Semi in April 2008. 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. The "CPU design team had developed a high-performance PowerPC processor under the leadership of Jim Keller and Pete Bannon."



Apple's interest doing its own central processing unit (CPU) design dates back to its $278 million acquisition of PA Semi in April 2008. 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. The "CPU design team had developed a high-performance PowerPC processor under the leadership of Jim Keller and Pete Bannon." ARM architecture license: Within a month of the PA Semi deal, "Apple secretly signed an architecture license with ARM that allowed the company to develop its own ARM-compatible CPUs, becoming one of the few companies in the world with that right."



Within a month of the PA Semi deal, "Apple secretly signed an architecture license with ARM that allowed the company to develop its own ARM-compatible CPUs, becoming one of the few companies in the world with that right." "Insanely great" runs into the laws of physics: One group of PA Semi employees worked on the Apple A4 chip using an ARM CPU core, while another group began "defining the microarchitecture for the new CPU." Steve Jobs' input, needless to say, set the pace. Jobs "initially set an 'insanely great' bar for the performance of the new CPU, but he eventually realized that his CPU team was limited by the same laws of physics that apply to everyone else," Gwennap wrote, citing a "source."



One group of PA Semi employees worked on the Apple A4 chip using an ARM CPU core, while another group began "defining the microarchitecture for the new CPU." Steve Jobs' input, needless to say, set the pace. Jobs "initially set an 'insanely great' bar for the performance of the new CPU, but he eventually realized that his CPU team was limited by the same laws of physics that apply to everyone else," Gwennap wrote, citing a "source." Departures: In March 2010, PA Semi's Dobberpuhl left Apple as did others in that time frame, such as COO Leo Joseph and VP of System Architecture Mark Hayter, "causing reports that the CPU design team was dissolving. But at PA Semi, Dobberpuhl and Joseph were involved mainly on the business side, and Hayter worked at the SoC (system-on-a-chip) level and not on the CPU, so these departures were not as significant as they appeared."



In March 2010, PA Semi's Dobberpuhl left Apple as did others in that time frame, such as COO Leo Joseph and VP of System Architecture Mark Hayter, "causing reports that the CPU design team was dissolving. But at PA Semi, Dobberpuhl and Joseph were involved mainly on the business side, and Hayter worked at the SoC (system-on-a-chip) level and not on the CPU, so these departures were not as significant as they appeared." Keller, Bannon, Williams : "Keller and Bannon continued to lead Apple's chip development...In February 2010, the company hired Gerard Williams, an ARM Fellow who was the technical lead for the Cortex-A8 and Cortex-A15 CPUs; Williams became Apple's chief CPU architect." Keller left Apple and went to AMD.



"Keller and Bannon continued to lead Apple's chip development...In February 2010, the company hired Gerard Williams, an ARM Fellow who was the technical lead for the Cortex-A8 and Cortex-A15 CPUs; Williams became Apple's chief CPU architect." Keller left Apple and went to AMD. A6: By early 2010, the team was done with the A6 microarchitecture design and started the physical-design phase. "To bolster its physical-design capabilities" Apple bought chip design house Intrinsity for about $120 million in April 2010. "This deal brought in an experienced team of chip designers that specialized in high-speed physical design, having just finished boosting the speed of Samsung's Hummingbird CPU (which Apple used in its A4 processor). The A6 taped out about a year later, and Apple received the first samples last summer. To support the iPhone 5 launch, the new processor must have been cleared for production around June," Gwennap wrote.



By early 2010, the team was done with the A6 microarchitecture design and started the physical-design phase. "To bolster its physical-design capabilities" Apple bought chip design house Intrinsity for about $120 million in April 2010. "This deal brought in an experienced team of chip designers that specialized in high-speed physical design, having just finished boosting the speed of Samsung's Hummingbird CPU (which Apple used in its A4 processor). The A6 taped out about a year later, and Apple received the first samples last summer. To support the iPhone 5 launch, the new processor must have been cleared for production around June," Gwennap wrote. North of $500 million spent: Apple spent about $400 million to buy PA Semi and Intrinsity, tens of millions for an ARM CPU license, and probably more than $100 million to support its CPU design efforts over a span of four years. "It appears that the end result will be that Apple ships a Cortex-A15-class CPU about three months before arch-enemy Samsung does."



So, what's Apple up to next? Gwennap believes Apple will have to do a new CPU design every two years, not unlike Intel's cadence.

Apple's next CPU "will likely implement the 64-bit ARMv8 instruction set," he wrote.

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Expect this in 2014, Gwennap said. "So for its 2013 products, Apple will have to rely on the same CPU design, perhaps in a quad-core configuration and with a higher-performance GPU."

Apple did not respond to a request for comment.