Editing Context switch (section)

=== Interrupt handling ===
Modern architectures are [[interrupt]] driven. This means that if the CPU requests data from a disk, for example, it does not need to [[busy-wait]] until the read is over; it can issue the request (to the I/O device) and continue with some other task. When the read is over, the CPU can be ''interrupted'' (by a hardware in this case, which sends interrupt request to [[Programmable interrupt controller|PIC]]) and presented with the read. For interrupts, a program called an ''[[interrupt handler]]'' is installed, and it is the interrupt handler that handles the interrupt from the disk.

When an interrupt occurs, the hardware automatically switches a part of the context (at least enough to allow the handler to return to the interrupted code). The handler may save additional context, depending on details of the particular hardware and software designs. Often only a minimal part of the context is changed in order to minimize the amount of time spent handling the interrupt. The [[Kernel (operating system)|kernel]] does not spawn or schedule a special process to handle interrupts, but instead the handler executes in the (often partial) context established at the beginning of interrupt handling. Once interrupt servicing is complete, the context in effect before the interrupt occurred is restored so that the interrupted process can resume execution in its proper state.