CPU: hey keyboard do you have anything for me?
CPU: hey keyboard do you have anything for me?
CPU: hey keyboard do you have anything for me?
CPU: hey keyboard do you have anything for me?
CPU: hey keyboard do you have anything for me?
CPU: hey keyboard do you have anything for me?
CPU: hey keyboard do you have anything for me?
CPU: hey keyboard do you have anything for me?
Keyboard: E
CPU: hey keyboard do you have anything for me?
CPU: hey keyboard do you have anything for me?
CPU: hey keyboard do you have anything for me?
CPU: hey keyboard do you have anything for me?
..
Modern USB keyboards need to be asked what's being pressed by the CPU multiple times a second, but old PS/2 keyboards will actually interrupt the CPU to send the key press command