Virtual Memory (Cambridge (CIE) O Level Computer Science): Revision Note

Cambridge IGCSE 0478 requires you to explain what virtual memory is, when it is used, and how it affects performance. This page is written using the structure and phrasing examiners expect in 2–4 mark answers.

Virtual memory does not increase the actual size of RAM. It creates temporary space on secondary storage. It makes the system usable, not faster.

A student uses software to create 3D models.

• 3D modelling often means processing large amounts of data

• This takes up a large amount of RAM

• If there is not enough physical RAM, virtual memory is used to:

  • Extend the RAMs capacity

  • Ensure the software does not freeze/crash when RAM gets full

A computer only has 4GB of RAM, Fynn says that virtual memory can be used instead of adding more RAM.

1. Explain how virtual memory can compensate for the lack of RAM in Fynn's computer [3]

2. Explain why it would be beneficial for Fynn to get more RAM instead of relying on virtual memory [2]

How to answer these questions

1. What is the definition of virtual memory? how does it work?

2. What is the downside of using virtual memory? turn this into an advantage of adding more RAM

Answers

• How can Virtual Memory compensate

  • Virtual Memory is used when RAM is full

  • ...part of the secondary storage used as (temporary) RAM

  • Data from RAM is moved to the secondary storage/Virtual Memory (to make space in RAM)

  • RAM can then be filled with new data

  • When data in Virtual Memory is needed it is moved back to RAM 

• Benefit of more RAM

  • More RAM will improve the performance of the computer // More RAM will speed up the access to data

  • Virtual Memory is slower to access than RAM direct (because it has to go back to RAM first)

  • Moving data between RAM and VM takes processor time