Some fun PC history:
https://computer.rip/2022-12-17-the-keyboard-controller.html
> These keyboard controllers were known to have a number of undocumented commands, the details of which depended on the mainboard vendor. And most interestingly, since they were general-purpose microcontrollers and had spare capacity after handling the keyboard, the 8042 in practice served as more of a general-purpose embedded controller. The term "keyboard controller" is a misnomer in this way, and it would probably be more accurate to call it an "embedded controller," but that term wasn't yet in use in the mid '80s.
https://computer.rip/2022-12-17-the-keyboard-controller.html
> These keyboard controllers were known to have a number of undocumented commands, the details of which depended on the mainboard vendor. And most interestingly, since they were general-purpose microcontrollers and had spare capacity after handling the keyboard, the 8042 in practice served as more of a general-purpose embedded controller. The term "keyboard controller" is a misnomer in this way, and it would probably be more accurate to call it an "embedded controller," but that term wasn't yet in use in the mid '80s.