Low End Mac’s Guide to Apple A-Series Processors

With the success of the iPhone, iPod touch, and iPad, Apple is a leading consumer of ARM processors, which it originally purchased from smartphone and tablet rival Samsung. Always looking for an edge, Apple has acquired a lot of design talent, which allowed it to produce its own CPUs.

In 2008, Apple acquired P.A. Semi, which had employees who had worked on DEC Alpha, StrongARM, Itanium, Opteron, and UltraSPARC CPUs. P.A. Semi had created its own PWRficient CPU designed as an independent PowerPC chip running at 1.8-2.0 GHz. These skills would be used to help develop new chips for iPhones, iPods, and more.

In 2010, Apple acquired Intrinsity, a company known for its efficient semiconductor logic designs and low power consumption. Intrinsity had worked on ARM, MIPS, and Power CPUs, including working with Samsung on the 1 GHz Cortex-A8, which is the same microarchitecture Apple’s A4 used.

Apple has also been building a chip development team in Israel since 2011, which now employs over 700.

Apple is on the cutting edge of chip technology, designing a new SoC (system-on-a-chip) every year. This article provides an overview of those developments.

2010: Apple A4

Apple A4 CPUThe A4 first appeared in the original iPad in early 2010, followed by the iPhone 4 and the 4G iPod touch later that year. The A4 is Apple’s adaptation of the Cortex-A8 design, a 32-bit superscalar chip roughly twice as powerful as its predecessors.

This is a single-core processor with 32 KB data and instruction caches plus a 512 KB level 2 cache. It also has a built-in PowerVR SGX535 graphics processor. The A4 is built using Samsung’s 45nm fabrication process. Speeds range up to 1 GHz, although Apple clocked it down in the iPhone and iPod touch to reduce heat and improve battery life.

The A4 is used with 256 MB of memory in the first iPad, the 4G iPod touch, and the 2G Apple TV. In the iPhone 4, is has 512 MB of memory. Memory is accessed using a 64-bit data bus.

All Cortex-A8 processors benefit from the work of Intrinsity, whether produced for Apple, Samsung, Freescale, TI, or other companies.

2011: Apple A5

Apple A5 CPUBased on the dual-core ARM Cortex-A9 processor, Apple’s 1 GHz A5 was introduced with the iPad 2 in March 2011. It next appeared in the dual-core iPhone 4S, the model that made Siri a standard feature, where it runs at 800 MHz to boost battery life and reduce heat. It has a 1 MB L2 cache.

In 2012, the A5 also made its way into the 5G iPod touch, the original iPad mini, and the 3G Apple TV, which used only one of the chip’s two cores.

In addition to two CPU cores, the A5 also has two GPU cores in the PowerVR SGX543MP2. The A5 was initially built using Samsung’s 45nm fabrication process and later moved to 32nm as Samsung improved its facilities.

Apple A5R3

Apple designed a special version of the A5 for a revised version of the 3G Apple TV. Where it had previously crippled one of the chip’s two cores, the new A5R3 was designed as a single-core CPU.

Apple A5X

The third generation iPad – and the first with a Retina Display – was built around the Apple A5X processor, a high performance variant of the A5 featuring a quad-core graphics processor, the PowerVR SGX543MP4, to keep up with the numerous pixels on the iPad’s Retina Display.

The A5X also has a 128-bit data path, twice that of earlier designs.

2012: Apple A6

Apple A6 CPUIntroduced with the iPhone 5 in September 2012, the A6 was the first Apple CPU to pass the 1 GHz mark – and by a fair margin at that. The dual-core chip runs at up to 1.3 GHz and is built around a custom Apple chip design rather than licensing an existing design from ARM as it had in the past.

The A6 integrates a triple-core PowerVR SGX543MP3 graphics processor. The A6 also includes 1 GB of memory, twice as much as the A5. It was produced by Samsung using its 32nm fabrication process.

The A6 was only used in iPhones and is at the heart of both the iPhone 5 and the iPhone 5C.

Apple A6X

Apple pushed the A6 design a bit further to power the 4G iPad. The A6X clocks at 1.4 GHz and has a quad-core graphics processor, the PowerVR 554MP4.

2013: Apple A7

Apple A7 CPUWith the Android world moving to some 4-core and even 8-core chips, Apple took a different tack with its next generation processor. The Apple A7 was the first 64-bit processor to end up in a smartphone or tablet.

The 64-bit A7 has twice as many registers as the A6, which makes for more efficient processing, and uses 64 KB data and instruction caches, double the size of earlier Apple CPUs. In addition to a 1 MB level 2 cache, the A7 also includes a 4 MB level 3 cache.

Graphics are handled by a quad-core PowerVR G6430 GPU. Additionally, the A7 includes a motion coprocessor, known as M7.

Introduced with the iPhone 5S on September 10, 2013, the A7 was underclocked to 1.3 GHz to reduce heat and improve battery life. The chip is built by Samsung using its 28nm fabrication process and includes over 1 billion transistors.

The A7 was used in the iPhone 5S, iPad mini 2, iPad mini 3, and original iPad Air. In the iPads, it runs at 1.4 GHz.

2014: Apple A8

Apple A8 CPUApple continued to plug away with annual improvements to its processor family, introducing the A8 at the same time as the 1.4 GHz iPhone 6 and 6 Plus in September 2014. In this case, while processing power was improved, the big deal was Apple reducing power draw by roughly 50% compared to the power hungry A7.

Rather than continuing to source it SoCs from its rival Samsung, Apple has the A8 fabricated by TSMC using a 20nm process. That process is a big part of the power drop, even though the A8 contains 2 billion transistors. This includes four-core PowerVR GX6450 graphics processor.

The A8 used in the iPhone 6 and 6 Plus has 1 GB of memory to work with, while the version found in the iPad mini 4 and 4G Apple TV includes 2 GB of memory. The version in the iPad mini 4 clocks at 1.5 GHz.

The A8 is also used in the 6G iPod touch, where it runs at 1.1 GHz.

Apple A8X

Once again, there was an enhanced version of Apple’s chip for its top-end iPad. The iPad Air 2 uses the A8X triple-core processor, Apple’s first foray beyond two cores. The A8X runs at 1.5 GHz and includes 3 billion transistors.

The A8X has an 8-core CPU, the PowerVR Series 6XT GXA6850A.

2015: Apple A9

Little is yet known about the A9 and A9X. The A9 is a dual-core processor with 2 GB of memory on the SoC and is clocked at 1.85 GHz in the iPhone 6S and 6S Plus. As of September 2015, it is the most powerful processor in a smartphone.

Apple is sourcing the chip from both Samsung and TSMC using 14nm and 16nm technology respectively. It has 64 KB level 1 data and instruction caches, 3 MB of level 2 cache shared by both cores, and 8 MB of level 3 cache used by the entire processor (not just the CPU cores).

Apple further boosts performance with a faster data path to memory and also to storage.

Apple A9X

Even less is known about the A9X, which is at the heart of the iPad Pro. Apple has announced it has twice the memory bandwidth and double the write speed of the A8X. We may need to wait until it ships in November to know much more.

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