A computer can appear to run several programs at the same time.
Explain one reason why an operating system schedules the processes running on a computer.
Mark scheme
Award up to two marks for a linked explanation such as:
- The operating system decides which process will use the CPU next (1) so the processor is shared between processes/processes take turns (1)
- The operating system allocates CPU time to each process/gives each process a small amount of time on the CPU (1) so multitasking can take place/several programs can appear to run at once (1)
- The operating system manages the state of each process, e.g. ready/running/blocked (1) so a process waiting for input/blocked does not stop other processes running (1)
- The operating system can terminate/end a process that has stopped responding (1) so it does not affect other processes/the computer keeps working (1)
For both marks, the expansion must follow/associate with the statement.
Do not accept the idea that the CPU runs two or more processes at exactly the same time; multitasking shares CPU time.
Do not accept 'the OS shares the CPU' on its own without saying how/why, e.g. giving each process a turn/CPU time.
Do not accept 'it stops programs crashing' without a link to process management, e.g. ending a process that has stopped responding.
Do not accept 'it manages processes' without saying what the operating system does.
Example answers and how they were marked
It decides which process will run on the CPU next so several programs can share the processor and appear to run at once.
Why: Linked point (1) and reason (1): CPU scheduling and shared processor.
It gives each program a small amount of time on the CPU.
Why: Point (1) only; it does not give a linked reason such as allowing multitasking.
The CPU runs all the programs at exactly the same time.
Why: Misconception: the CPU does not run processes at exactly the same time; no creditworthy point.