Explain the need for scheduling in process management.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

1. [1] (a) One mark for each point (Max 3) • Process scheduling allows more than one program/task to appear to be executed at the same time / enables multi-tasking / multiprogramming.
2. [1] (a) • To allow high priority jobs to be completed first.
3. [1] (a) • To keep the CPU busy all the time
4. [1] (a) • ... to ensure that all processes execute efficiently
5. [1] (a) • ... and to have reduced wait times for all processes / to ensure all processes have fair access to the CPU / prevent starvation of some processes.
6. [1] (b) One mark for each point (Max 2) for Shortest job first: • Process are executed in ascending order of the amount of CPU time required // Short processes are executed first and followed by longer processes.
7. [1] (b) ...which leads to an increased throughput (because more processes can be executed in a smaller amount of time).
8. [1] (b) One mark for each point (Max 2) for Round robin: • Each process is served by the CPU for a fixed time/time slice (so all processes are given the same priority).
9. [1] (b) • Starvation doesn't occur (because for each round robin cycle, every process is given a fixed time/time slice to execute).
10. [1] (b) One mark for each point (Max 2) for First come first served: • No complex logic, each process request is queued as it is received and executed one by one.
11. [1] (b) • Starvation doesn't occur (because every process will eventually get a chance to run) // less processor overhead.