Virtual Memory


Virtual Memory

What is virtual memory?

  • Virtual memory is an extension of primary storage (RAM) located on secondary storage

  • In situations where RAM is close to being full, virtual memory can be used so that the computer remains operational

  • Programs and data not currently being executed are transferred to virtual memory

  • Programs and data are transferred back to RAM when they are needed

  • Virtual memory is much slower than RAM and it's use will impact negatively on system performance

  • To avoid the use of virtual memory, increase the size of the RAM

RAM (primary storage)

 

Virtual Memory (secondary storage)

Spreadsheet Software

Operating System

⇔

 

 

 

Video Editing Software

  • In the example above, the computer is turned on and the elements of the operating system are loaded into RAM

  • The user opens some spreadsheet and video editing software but RAM is full

  • The program not currently being used (video editing) is transferred to virtual memory

RAM (primary storage)

 

Virtual Memory (secondary storage)

Video Editing Software

Operating System

⇔

 

 

 

Spreadsheet Software

  • When the user want to use the video editing software again, it is transferred back from virtual memory to RAM

Worked example

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