The ECU is a computer, a packaged bundle of chips which plugs in to wires and does nothing but communicate to other components via those wires. That's what an electronic control unit means.
The driven devices, amplifiers etc. are under the control of the control unit. They are not part of the control unit. They're located in areas subject to much more heat and mechanical stress, and in most cases (ignition coils excepted) are mechanical in function.
Because...
The driven devices, amplifiers etc. are under the control of the control unit. They are not part of the control unit. They're located in areas subject to much more heat and mechanical stress, and in most cases (ignition coils excepted) are mechanical in function.
I'm not talking about the driven devices.
Here's a diesel example in video form:
https://www.youtube.com/watch?v=4k-G1dMgFUo
Here's one in gasoline form:
Injector drivers and ignition drivers are part of the control unit.