In his More Color column for Macworld this week, Jason Snell writes about what the T2 chip in the new iMac Pro does. (My Late 2016 Touch Bar MacBook Pro has a T1.)
Notably, here’s an excerpt on booting up the machine:
When you start up the iMac Pro, the familiar Apple logo appears almost immediately. This is a sign that the T2 is taking control. For security reasons, the T2 is the iMac Pro hardware’s “root of trust,” and it validates the entire boot process when the power comes on. The T2 starts up, checks things out, loads its bootloader, verifies that it’s legitimate and cryptographically signed by Apple, and then moves on to the next part of the boot process.
This new boot process means there’s also a new utility for Mac users to get to know: Startup Security Utility, which you can only access by booting into Recovery mode by holding down Command-R while starting up. Startup Security Utility gives the T2 guidance about just how strict it should be when judging whether it should boot your computer.