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Edexcel GCSE Computer Science (1CP2) Exam Questions

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4 questions · 8 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.

2Describe2 marksUser Management Swap Remove

A computer can be used by more than one person.

Describe how an operating system uses access rights to protect each user's files.

[2 marks]
Mark scheme

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

  • Each user/file is given permissions/access rights (1) so other users cannot read/write/open/change that user's files (1)
  • A user may be given read-only/read access to a file (1) so they cannot edit/delete/change it (1)
  • Each file is given permissions/access rights for different users (1) so the operating system allows/refuses access depending on which user is logged in (1)
  • The operating system checks a user's permissions/access rights when a file is opened (1) so a user with read-only/read access cannot save/delete changes (1)

Do not accept responses about asking for a password/username, as this checks who the user is, not what they are allowed to do.

Do not accept 'files are protected/safe' or 'access rights protect files' without saying how access is limited (e.g. read-only access, permissions for different users).

Example answers and how they were marked
Full marks2/2

A user can be given read-only access to a file, so they can open it but cannot edit or delete it.

Why: Read-only/read access point (1) and linked development that the user cannot edit/delete the file (1).

Some marks1/2

A user can be given read-only access to a file.

Why: Read-only/read access point (1); no development saying what this prevents, such as being unable to edit/delete the file (0).

No marks0/2

The operating system asks for the password again before the file opens.

Why: Describes asking for a password, which checks who the user is, not access rights to the file; no creditworthy point.

3Explain2 marksProcess Management Swap Remove

A user opens a web browser.

Explain what the operating system does to get the browser's process ready to run.

[2 marks]
Mark scheme

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

  • A process is created for the program (1) so that its instructions can be loaded into RAM (1)
  • The process is put into the ready state (1) so that it can wait for the CPU to become available (1)
  • The operating system adds the process to a queue of ready processes (1) so the scheduler can choose it when the CPU is free (1)
  • The operating system allocates the resources the process needs (1) so that it can start running when it is given CPU time (1)

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

Allow 'main memory' for RAM.

Do not accept 'the browser is downloaded/loaded from the internet'.

Do not accept 'the program is run immediately on the CPU' without the ready step.

Example answers and how they were marked
Full marks2/2

It creates a process and loads the browser's instructions into RAM, then puts the process in the ready state to wait for CPU time.

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

Some marks1/2

It moves the program into RAM.

Why: A correct point (1) but no linked reason about the process being made ready.

No marks0/2

It runs the program straight away on the CPU.

Why: This describes the running state, not making the process ready, so no credit.

4Explain2 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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