The keyup event used in various programming framework is raised from keyboard? Is the circuit of keyboard to generate the event or the event is deducted by operating system?
Keyboard operations are electronically processed by circuitry inside the device. So every action emits interrupt, which is processed by top-level system, like the OS. So various frameworks are subscribed to the events generated by it. Further details on how interrupt system works can be found at http://en.tldp.org/HOWTO/Unix-and-Internet-Fundamentals-HOWTO/devices.html