Interrupts

In Real Mode, this is usually the Interrupt Table configured by the BIOS - https://www.ctyme.com/rbrown.htm

• In Protected Mode or Long Mode, this is usually configured in the Global Descriptor Table to point to functions in the running operating system, so it can trigger and handle Interrupt Requests

Interrupts are events that can be triggered on the processor, either by the operating system or the hardware, to interrupt the operating system (or BIOS, in Real Mode) and run a function.

In effect, these are callbacks, as you might be used to in high-level languages