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Edexcel GCSE Computer Science (1CP2) Exam Questions

Build a practice paper from 631 exam-style questions, each with its mark scheme and example answers. Print it, or answer it on paper and then open the mark schemes. Or browse the questions by topic.

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3 questions · 6 marks

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1Describe2 marksMemory Management Swap Remove

The operating system is held in main memory while the computer is running.

Describe how the operating system stops a running program from overwriting memory that is not its own.

[2 marks]
Mark scheme

Award up to two marks for a linked description such as:

  • It keeps a record of which memory addresses/areas belong to each program and to the operating system (1) so it knows which addresses a program is allowed to use (1)
  • Each program is given its own area of main memory (1) so a program cannot write to the addresses used by another program or by the operating system (1)
  • The memory used by the operating system is marked as protected/reserved (1) so a program that tries to write to it is blocked/causes an error (1)
  • The address a program writes to is checked against the record of its allocated area (1) and the write is stopped if the address is outside that area (1)

Allow the memory being protected to be that of the operating system or of another program.

For both marks, the expansion must follow/associate with the statement.

Do not award generic answers such as 'the operating system manages memory' or 'the operating system keeps track of memory'.

Do not award responses about stopping programs using too much memory or allocating memory, as these are not about protecting memory being overwritten.

Do not award responses about virtual memory, paging or moving processes to secondary storage.

Do not award responses about firewalls, antivirus software or passwords.

Example answers and how they were marked
Full marks2/2

The operating system gives each program its own area of main memory so that a program cannot write to the addresses used by another program or by the operating system.

Why: Each program is given its own area of main memory (1) linked to it not being able to write to the addresses used by another program or the operating system (1).

Some marks1/2

The operating system gives each program its own area of main memory.

Why: Each program is given its own area of main memory (1), but there is no linked development saying how this stops a program overwriting memory that is not its own.

No marks0/2

The operating system stops a program overwriting memory by moving it into virtual memory when it uses too much.

Why: This describes virtual memory and limiting how much memory a program uses, not protecting memory from being overwritten, so neither bullet applies and the Do not award lines rule it out.

2Explain2 marksProcess Management Swap Remove

A computer has a single CPU.

Explain how the operating system allows a user to run several programs at the same time.

[2 marks]
Mark scheme

Award up to two marks for a linked explanation such as:

  • The operating system switches rapidly between processes (1) so each process runs for a short time slice before the next one starts (1)
  • Each process is given a small amount of CPU time (1) so the CPU moves on to another process when that time is up (1)
  • The operating system chooses which process to run next (1) so the CPU is shared between the programs (1)
  • Processes take turns to use the CPU (1) because the CPU is so fast the user does not notice the switching (1)
  • Only one process can run on the CPU at a time (1) so the operating system must swap processes in and out quickly (1)

For both marks, the expansion must follow/associate with the statement.

Allow 'time slice' / 'time quantum'.

Do not accept 'the computer has more than one CPU' / 'each program runs on its own CPU'.

Do not accept 'the CPU does two things at once' without saying processes take turns/are switched.

Example answers and how they were marked
Full marks2/2

The operating system switches rapidly between processes, giving each one a small time slice, so the CPU is shared and the programs appear to run together.

Why: Linked point (1) and reason (1).

Some marks1/2

Each process is given a small amount of CPU time.

Why: A correct point (1) but no linked reason.

No marks0/2

The computer has two CPUs so each program can run on its own processor.

Why: The scenario states a single CPU, so this misconception earns no credit.

3Explain2 marksPurpose & Function of Operating Systems Swap Remove

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.

[2 marks]
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
Full marks2/2

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.

Some marks1/2

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.

No marks0/2

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.

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