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Edexcel GCSE Computer Science (1CP2) Exam Questions

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2 questions · 4 marks

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1Describe2 marksMemory Management Swap Remove

An operating system keeps a record of the memory it has allocated to each program.

Describe how this record is used.

[2 marks]
Mark scheme

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

  • The start and end address/size of the block allocated to each program is recorded (1) so the operating system knows which areas of main memory are in use and which are free (1)
  • The record is checked before memory is allocated (1) so memory already in use is not given to another program/is not overwritten (1)
  • The record is searched for a free block that is large enough (1) so a newly loaded program is placed in a suitable area of main memory (1)
  • The record is updated when a program ends/closes (1) so the memory it was using is marked as free for other programs (1)

Allow the record to be called a memory map/memory table/allocation table.

A response that only says the operating system keeps a record/list of the memory each program is using, without saying what the record contains, earns 0 marks.

A response that states what the record contains, e.g. the addresses/the start and end address of each block, earns 1 mark even if it does not say how the record is used.

Do not accept responses about saving programs/files to secondary storage or about moving programs to virtual memory, as these are not uses of this record.

Example answers and how they were marked
Full marks2/2

The operating system records the start and end address of the block of memory given to each program so that it does not give the same memory to another program.

Why: The start and end address of each block is recorded (1) linked to memory already in use not being given to another program (1).

Some marks1/2

The operating system records the start and end address of the memory used by each program.

Why: States what the record contains (1), but does not develop how the record is used, so the second mark is not earned.

No marks0/2

The operating system saves the programs to the hard disk so there is enough memory for other programs.

Why: Describes moving programs to secondary storage rather than how the record of allocated memory is used; no creditworthy point is made.

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.

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