Bootloaders used on Xbox One.
Primary bootloader that is used for initialising the Security Processor, decrypting the future stages, verifying the console certificates, fuses and more. This sequence is split into 3 boot stages.
Started after the SP has completed its boot. Proceeds to intialise the rest of the console and then begins booting into the Host VBI.
(S)treaming (C)rypto (P)rocessor - internal crypto engine on the APU die. Data blob thats uploaded to the SCP, for initialization?! Initialization phase: Unknown, somewhere in between 2BL and VBI.
Final boot stage which initialises the critical components of the operating system and essentially acts as a bootstrap.