APL1023, also known as X619AP or the Apple T1 Security chip, is an derivative of the S2 that controls the Touch Bar's display, Touch ID sensor, Apple Pay, and other Secure Enclave-enabled features of the following Macs:
- MacBook Pro (15-inch, 2016)
- MacBook Pro (13-inch, Four Thunderbolt 3 ports, 2016)
- MacBook Pro (15-inch, 2017)
- MacBook Pro (13-inch, Four Thunderbolt 3 ports, 2017)
The T1 has two model identifiers: iBridge1,1 and Watch2,5, and runs a variant of watchOS 3 named embeddedOS, which is loaded via a ramdisk upon boot.
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