ITPEC FE Morning April 2018 Question 19
ITPEC FE Morning April 2018 — Question 19 of 80
Context Switch (Process Switching) — the OS procedure for switching the CPU from one process to another.
When an interrupt occurs, the OS performs three steps in order:
- •A: Saving of the running state — save the current process's context (registers, program counter) so it can resume later
- •B: Selection of the process — the scheduler picks the next process from the ready queue
- •C: Restoration of the running state — load the selected process's saved context into the CPU
The fixed order is always: Save → Select → Restore
Why not others:
- (a) Restore before Save — cannot restore a new process without first saving the old one
- (b) Restore before Select — cannot restore a process that hasn't been selected yet
- (d) Select before Save — selecting a new process before saving the current one risks losing its state
Key rule: Context switch order is always Save → Select → Restore. The current process must be preserved before any new process can be chosen or loaded.
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