An operating system keeps a record of the memory it has allocated to each program.
Describe how this record is used.
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
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).
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.
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.