OCR J277 Mark Scheme - Virtual Memory

OCR	GCSE (9-1) Computer Science Mark Scheme J277/01: Unit 1.2 Virtual Memory

Question	Answer	Marks	Guidance
1a	Secondary Storage / Hard Disk Drive / SSD (1)	1	AO1 (Knowledge) Do not accept: "The Cloud" or "Internet". Do not accept: "RAM" or "ROM".
1b	It is used when RAM is full / nearly full [1] To prevent the computer from crashing / to allow more programs to be opened [1]	2	AO1 (Knowledge) Must reference RAM being full/insufficient. "When the memory is full" is BOD (Benefit of Doubt), but students should specify RAM.
2	Data/instructions that are not currently being used... [1] ...are transferred from RAM to Virtual Memory (to make space) [1] When the data is needed again, it is transferred back to RAM [1]	3	AO1 (Knowledge) The key mechanism is the transfer of data between the two locations. Accept references to "swapping" or "paging" if the direction of data movement is clear.
3	Virtual Memory is on secondary storage [1] Secondary storage has a slower access speed / slower read-write speed than RAM [1] The processor has to wait while data is moved back into RAM [1] This constant moving of data (disk thrashing) causes the delay [1]	4	AO1 (Knowledge) & AO2 (Application) Max 4 marks. Must link the slowness to the speed difference between RAM and Secondary Storage. Simply saying "It takes time to move data" gets 1 mark. Explaining why (read/write speeds) gets the higher marks.