The new iPhone is a fast phone. The iPhone tear-down detailed below reveals that the processor A9 is packaged together with the mobility processor M9. "A9 package itself appears bigger—roughly 14.5 x 15 mm, up from 13.5 x 14.5 mm on the A8. That could represent a smaller die plus the addition of the embedded M9"
Placing both processors in close proximity in one package reduces the delay in operations that use both processors. For example operations using the new 3D touch technology.
In addition, increasing the DRAM size to 2GB LPDDR4 DRAM , also increase the speed of the phone by providing additional storage enabling more operations to occur at the same time in parallel.
It is also interesting that the battery "1715 mAh. It's a small but notable decrease from the 1810 mAh battery in last year's iPhone 6 " is smaller. Using one package for A9 and M9 processors, and a larger LPDDR4 DRAM help to reduce power consumption.
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