|From September 9, 2014 to Present|
|1.1 GHz (iPod Touch 6th generation) to 1.4 GHz (iPhone 6, iPhone 6 Plus) and 1.5 GHz (iPad mini 4 & Apple TV (4th Gen))|
|A64, A32, T32|
|Per core: 64 KB instruction + 64 KB data|
|1 MB shared|
|PowerVR Series 6XT GX6450 (quad-core)|
The Apple A8 is a 64-bit ARM-based system on a chip (SoC) designed by Apple Inc. It first appeared in the iPhone 6 and iPhone 6 Plus, which were introduced on September 9, 2014. Apple states that it has 25% more CPU performance and 50% more graphics performance while drawing only 50% of the power of its predecessor, the Apple A7.
The A8 is manufactured on a 20 nm process by TSMC, which replaced Samsung as the manufacturer of Apple's mobile device processors. It contains 2 billion transistors. Despite having twice the number of transistors of the A7, the A8's physical size has been reduced by 13% to 89 mm. The A8 uses LPDDR3-1333 RAM on a 64-bit memory interface; in the iPhone 6 and 6 Plus the A8 has 1 GB RAM included in the package, while the A8 in the iPad Mini 4 and 4th generation Apple TV is packaged with 2 GB RAM.
The A8 CPU has a per-core L1 cache of 64 KB for data and 64 KB for instructions, an L2 cache of 1 MB shared by both CPU cores, and a 4 MB L3 cache that services the entire SoC. As its predessor It's a 6 decode, 6 issue, 9 wide, out-of-order design. The processor is dual core, and as used in the iPhone 6 has a frequency of 1.4 GHz, supporting Apple's claim of it being 25% faster than the A7. It also supports the notion of this being a second generation enhanced Cyclone core called Typhoon, and not an entirely new architecture which would supposedly mean a more significant performance gain per Hz.
On October 16, 2014, Apple introduced a variant of the A8, the A8X, in the iPad Air 2. Compared with the A8, the A8X has an enhanced 8-shader-cluster GPU and improved CPU performance due to one extra core and higher frequency.
The A8's branch predictor has been claimed to infringe on a 1998 patent. On October 14, 2015, a district judge found Apple guilty of infringing U.S. patent US 5781752 , "Table based data speculation circuit for parallel processing computer", on the Apple A7 and A8 processors. The patent is owned by Wisconsin Alumni Research Foundation (WARF), a firm affiliated with the University of Wisconsin. On July 24, 2017, Apple was ordered to pay WARF $506 million for patent infringement. The patent expired in December 2016.