When data and instructions are stored in the main memory. When needed they FDE
Inside a computer’s processor is the system clock, a device that generates a timing signal which changes at a regular frequency. This signal is used to synchronise communication between the components of the processor and the rest of the computer system.
Between each execute stage and fetch stage of the cycle, the content of the status register is checked for changes that could show the occurrence of an interrupt.
An interrupt is a signal sent to the processor by another part of the computer requesting the attention of the processor. it is detected as a change in the content of the status register in the FDE cycle.