IBridge

iBridge is a family of embedded processing devices for Intel-based Macs. There are two major variants.

iBridge T1 - found in the following Macs: iBridge T2 - found in the following Macs:
 * MacBook Pro (13-inch, 4 Thunderbolt 3 ports, 2016)
 * MacBook Pro (15-inch, 2016)
 * MacBook Pro (13-inch, 4 Thunderbolt 3 ports, 2017)
 * MacBook Pro (15-inch, 2017)
 * iMac Pro (2017)
 * MacBook Pro (13-inch, 4 Thunderbolt 3 ports, 2018)
 * MacBook Pro (15-inch, 2018)
 * Mac mini (2018)
 * MacBook Air (Retina, 13-inch, 2018)
 * MacBook Pro (13-inch, 4 Thunderbolt 3 ports, 2019)
 * MacBook Pro (15-inch, 2019)
 * MacBook Air (Retina, 13-inch, 2019)
 * Mac Pro (2019)
 * MacBook Pro (13-inch, 2 Thunderbolt 3 ports, 2019)
 * MacBook Pro (16-inch, 2019)
 * MacBook Air (Retina, 13-inch, 2020)
 * MacBook Pro (13-inch, 2 Thunderbolt 3 ports, 2020)
 * MacBook Pro (13-inch, 4 Thunderbolt 3 ports, 2020)
 * iMac (Retina 5K, 27-inch, 2020)

iBridge devices run a heavily modified version of watchOS, titled bridgeOS, and they power various functions on Intel-based Macs.
 * Touch Bar (MacBook Pro only)
 * Touch ID (Mac laptops only)
 * System management controller
 * Microphone hardware disconnect (Mac laptops and T2 only)
 * HEVC 8- and 10-bit encoding (T2 only)
 * Image and audio signal processing (T2 only)
 * Apple Secure Boot (T2 only)