iMac Pro Will Reportedly Have an A10 Fusion Coprocessor Alongside X86 Chip

Chaim Gartenberg:

But, as Pepijn Bruienne pointed out, the bigger implication of the A10 Fusion is for a less user-facing function, with Apple likely to use the coprocessor to enable SecureBoot on the iMac Pro. In more practical terms, it means that Apple will be using the A10 Fusion chip to handle the initial boot process and confirm that software checks out, before passing things off to the regular x86 Intel processor in your Mac.