I/O interrupts

Interrupts in this case mean that the current application is interrupted, and the I/O device is serviced.
The classic example of the is when there is a download going on.
The PC can be running other applications, and when the FIFO of the UART in the MODEM is almost full of data, it sends an interrupt to the CPU.
The CPU jumps to the service routine for the Serial Port (MODEM), transfers the data to a buffer or file (Depending on setup) and then exits the interrupt routine back to whatever itwas doing before the interrupt occurred.
A lot of interrupts occur in a PC all the time.
The most regular is of course the interrupt to update the time.
Regards, Chris

When an interrupt happens the computer goes to a section of programming that processes what the interrupt needs to be done.

Then when finished, the computer returns to the programming it was running originally.