Jason Snell, Macworld:

The T2 processor isn’t doing the heavy lifting in the iMac Pro—that’s the Intel Xeon processor with between 8 and 14 processor cores. The T2 is the brain behind that brain, running the subsystems of the iMac Pro from a single piece of Apple-built silicon. The result is a simplified internal design that doesn’t require multiple components from multiple manufacturers.

Jason does a nice job here, digging into what makes an iMac Pro different than its ancestors. Pay special attention to the section “Boot twice for safety”. Very interesting.