BMC (baseboard management controller)
Beginner
A tiny extra computer inside the server. It watches temperatures and power. Staff can use it to fix the machine from far away, even when it is off.
Novice
A small, always-on processor on the server board with its own network port. It reads sensors, controls fans and power, keeps logs and offers a remote screen and keyboard, independent of the main CPUs and their operating system.
Expert
An out-of-band management SoC (often Arm-based, running OpenBMC or vendor firmware) on standby power. It exposes Redfish and IPMI, mediates firmware updates, and with a hardware root of trust verifies firmware. DC-SCM moves it onto a separate module.