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OCR H446 1.2.1 Virtual memory

Part 3 of 12 · H446 1.2.1 · Systems software

Virtual memory looks like extra RAM and behaves nothing like it, which is the misconception H446 1.2.1 keeps testing. This worksheet traces the managed movement of pages between RAM and secondary storage, then follows the chain from a missing page to much slower access and, once it repeats, thrashing.

Students will:

  • describe how the operating system moves pages between RAM and secondary storage
  • explain why describing virtual memory as extra RAM is misleading
  • link repeated swapping to slower access and to thrashing
  • state one benefit and one drawback of using virtual memory
  • tell virtual memory, virtual storage and virtual machines apart in context

Inside: 6 explanation cells, 6 multiple-choice questions, 2 fill-in-the-blanks cells and 3 written answers. 28 marks, about 35 to 45 minutes.

Series: H446 1.2.1 · Systems software, part 3 of 12.

Shared by Coding PathwayVerified teacher

  • 17 cells
  • About 45 minutes
  • CC BY-SA 4.0
  • Shared 31 Aug 2026
  • Updated 3 Sept 2026

Preview

The whole resource, exactly as a class sees it. Answers and marking are held back.

Virtual memory

A program must have the instructions and data it currently needs in RAM. If there is not enough free RAM for every active page, the operating system can temporarily use part of secondary storage as virtual memory.

Virtual memory increases the apparent memory available, but it does not make secondary storage as fast as RAM.

You should already know: paging divides programs into fixed-size pages.

Worked model: swap what is needed

Virtual memory swaps pages between RAM and secondary storageRAMpage Apage Bpage Cpage Dsecondary storagepage Epage Fother dataother dataless-needed page outneeded page inStorage access is much slower than RAM; excessive swapping causes thrashing.

When RAM is full and a needed page is on secondary storage, the operating system selects a less-needed page in RAM, writes it out if necessary, and loads the required page into the freed location. Its page mapping is updated.

When the processor later needs a page that is not in RAM, another transfer may be required. This lets larger or more numerous programs continue to run, but storage transfers are slow.

Multiple choice1 mark

When is virtual memory normally used?

  • AWhenever the processor clock is increased
  • BWhenever a file is backed up
  • CWhen available RAM is insufficient for the active programs and data
  • DOnly when no secondary storage exists
Fill in the blanks5 marks
Put the virtual-memory mechanism into words: the OS identifies a needed entry 1 that is not in RAM, selects a less-needed page to move to entry 2, loads the required page into entry 3, updates the page entry 4 and then allows execution to entry 5.
Multiple choice1 mark

Which explanation correctly connects memory division to virtual memory?

  • APaging compresses every program before the BIOS loads it
  • BSegmentation makes secondary storage operate at RAM speed
  • CVirtual memory removes the need to divide or track memory
  • DThe OS can move needed pages, or segments in a segmented model, between RAM and secondary storage; mappings track where divided memory is held
Multiple choice1 mark

Why is it misleading to describe virtual memory as ‘extra RAM’?

  • AIt is a second processor register
  • BIt permanently increases the physical RAM chips
  • CIt stores only user-interface images
  • DIt is normally an area of slower secondary storage managed to supplement RAM

Worked performance chain

Suppose an application repeatedly alternates between two sets of pages, but RAM can hold only one set.

  1. A required page is absent from RAM.
  2. The OS swaps pages between RAM and storage.
  3. The processor waits for much slower storage access.
  4. If this happens repeatedly, more time is spent moving pages than executing useful instructions.
  5. The system becomes extremely slow. This excessive swapping is called thrashing.
Multiple choice1 mark

Which component makes virtual-memory access much slower than ordinary memory access?

  • ASecondary storage
  • BThe arithmetic logic unit
  • CThe program counter
  • DThe control bus alone
Written answer4 marks

Explain how virtual memory allows a program to continue when RAM is nearly full.

Describe movement in both directions and why it creates usable RAM space.

Students type their answer here.

Multiple choice1 mark

What does thrashing mean in this context?

  • AThe CPU executes the same arithmetic instruction repeatedly
  • BThe system spends excessive time swapping pages between RAM and storage
  • CThe file system deletes fragmented files
  • DThe BIOS repeats its hardware test
Written answer4 marks

Explain one benefit and one drawback of using virtual memory.

Develop each point beyond a label.

Students type their answer here.

Keep three virtual ideas separate

TermMeaning
Virtual memorysecondary storage temporarily supplements RAM
Virtual storageremote or abstracted storage appears like a local storage location
Virtual machinesoftware takes on the function of a machine

OCR examiner commentary records confusion between these ideas. Identify the resource being imitated or supplemented before explaining it.

Multiple choice1 mark

A remote drive appears in a user's file manager as if it were a local disk. Which term best fits?

  • AVirtual memory
  • BPage table
  • CVirtual storage
  • DInterrupt service routine
Written answer5 marks

A student opens a video editor, a graphics package and several large browser tabs on a laptop with limited RAM. Explain why the laptop may first continue to operate and then become very slow.

Use the terms page, RAM, secondary storage and thrashing.

Students type their answer here.

Closed-book checkpoint

Complete the causal chain from memory. Checking is held for teacher review.

Fill in the blanks4 marks
Virtual memory is activated when active demand exceeds the installed main-memory entry 1. The OS transfers sections to and from entry 2 storage. Because this medium has greater access entry 3, frequent transfers reduce performance; excessive swapping is called entry 4.

Review your understanding

Before submitting, check that you can explain the main distinction in your own words, apply it in an unfamiliar context and justify each consequence rather than only naming a feature.