Community resourceWorksheet

J277 1.2.1 Primary storage

Part 1 of 6 · J277 1.2.1-1.2.3 · Memory and storage

The opening worksheet on memory and storage, covering RAM, ROM and where cache fits.

Students will:

  • explain why a computer needs primary storage
  • compare RAM and ROM
  • describe the purpose of each
  • explain the role of cache
  • replace the vague storage answers examiners penalise

Inside: 7 explanation cells, 4 multiple-choice questions, 1 fill-in-the-blanks cell and 4 written answers. 27 marks, about 60 minutes.

Series: J277 1.2.1-1.2.3 · Memory and storage, part 1 of 6.

Shared by Coding PathwayVerified teacher

  • 16 cells
  • About 60 minutes
  • CC BY-SA 4.0
  • Shared 17 Aug 2026
  • Updated 9 Sept 2026

Preview

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

Memory and storage 1: primary storage

When you open an application, the computer needs somewhere fast to hold the instructions and data being used. It also needs some instructions to remain available when the power is off. Primary storage helps meet these needs.

The names may be new, but you will meet them one at a time. You do not need to have studied CPU architecture first. By the end of this worksheet, you should be able to:

  • explain why a computer needs primary storage
  • compare RAM and ROM
  • describe the purpose of RAM and ROM
  • explain the role of cache
  • apply these ideas to familiar computer systems

Cache is introduced here alongside RAM and ROM. If you have met cache in another topic, use that knowledge as a helpful reminder.

Work through the explanation, checks and applications in order. Use the final challenge to connect several ideas.

1. Why primary storage is needed

The CPU processes data and instructions, but it needs quick access to them. Primary storage is memory that the CPU can access directly.

When an application is opened, the instructions and data currently needed are copied from secondary storage into RAM. Accessing RAM is much faster than repeatedly retrieving everything from secondary storage.

Primary storage in this specification includes RAM, ROM and cache. They do not all have the same purpose.

Multiple choice1 mark

Why does a computer need primary storage?

  • ATo connect the computer to every network automatically
  • BTo give the CPU fast access to data and instructions needed for processing
  • CTo provide unlimited permanent storage
  • DTo replace every secondary storage device

2. Random Access Memory (RAM)

RAM is the computer's main working memory.

  • It stores instructions and data currently in use.
  • It is volatile, so its contents are lost when the power is switched off.
  • Its contents can be read and changed.

Be precise about “currently in use”. An entire installed application is held in secondary storage. The parts currently needed are loaded into RAM.

3. Read Only Memory (ROM)

ROM stores fixed instructions, programs or reference data that must remain available when the power is off.

  • Firmware is software built into a device to help control its hardware.
  • In a general-purpose computer, ROM can hold start-up firmware, such as instructions used to check hardware and begin the start-up process. BIOS and UEFI are familiar examples, but the assessed idea here is the purpose of ROM rather than memorising those names.
  • In an embedded system, ROM can hold the fixed control program needed by the device.
  • It is non-volatile, so its contents remain without power.
  • Its contents are not normally changed during ordinary use.

Historically, ROM was also used to hold fixed system routines, software and games, including software on some game cartridges. Modern devices often use rewritable flash memory for firmware, but the OCR model of ROM is still a non-volatile, normally read-only store for fixed instructions.

ROM is not the same as ordinary secondary storage. Both are non-volatile, but secondary storage is normally much larger and is regularly used to save and change applications, an operating system and user files.

When comparing RAM and ROM, give both sides: RAM is volatile, whereas ROM is non-volatile.

Use both sides of this comparison in an explanation. Volatility is important, but purpose and contents are what make the answer complete.

Comparison of RAM and ROM when power is on and off RAM holds currently used programs and data while powered and loses the contents when power is removed. ROM holds startup instructions or firmware and retains them without power. Primary storage: purpose + contents + power state RAM While powered holds programs and data currently in use When power is removed contents are lost: volatile read from and written to during use ROM While powered provides startup instructions or firmware When power is removed contents are retained: non-volatile normally read, not changed in routine use Do not replace these roles with the vague labels “temporary” and “permanent”.
Fill in the blanks4 marks
RAM is label 1 memory that holds data and instructions currently in use. ROM is label 2 memory and can hold label 3. RAM is normally label 4, while ROM is normally read only.
  • non-volatile
  • output only
  • start-up instructions
  • volatile
  • read and write
  • permanent user files
Multiple choice, several answers3 marks

Which three are reasonable examples of fixed information suited to ROM? Select all that apply.

  • AInstructions used to start a computer and check its hardware
  • BA student's editable folder of photographs
  • CThe fixed control program in an embedded thermostat
  • DEvery document saved by all users
  • EGame software held in a historic read-only cartridge
Written answer4 marks

Compare RAM and ROM. Give two clear differences.

For each difference, state what is true of RAM and what is true of ROM. Consider volatility, purpose or whether contents normally change.

Students type their answer here.

4. Where cache fits

Cache is small, fast memory located in or close to the CPU. It stores frequently or recently used data and instructions so that the CPU can access them more quickly than if it had to retrieve them from RAM.

A useful comparison is:

  • cache is smaller and faster than RAM
  • RAM is larger but slower than cache
  • both support the CPU while programs are running

Cache does not permanently store a user's documents. It improves access to items the processor is likely to need soon.

Multiple choice, several answers3 marks

Which three statements are accurate? Select all that apply.

  • AROM loses all its contents when power is removed
  • BRAM can hold data currently being processed
  • CCache is a high-capacity replacement for secondary storage
  • DROM can hold instructions used when a computer starts
  • ECache can hold frequently used data and instructions close to the CPU
Written answer3 marks

A student opens a photo-editing application and begins changing an image. Give one example of something that could be held in RAM and explain why it is there.

Choose something currently being used, such as part of the application, the open image data or a recent change.

Students type their answer here.

5. Avoid vague storage answers

These phrases are too vague on their own:

  • “RAM stores programs.”
  • “ROM stores important things.”
  • “Cache makes it faster.”

Improve them by naming what is stored and why:

  • RAM stores the data and instructions currently being used.
  • ROM stores fixed start-up or control instructions that must remain when power is removed.
  • Cache stores frequently or recently used data and instructions, reducing the time the CPU waits to access them from RAM.
Written answer2 marks

A computer is switched on after being completely disconnected from power. Explain why ROM is suitable for storing its start-up instructions.

Link the loss of power to non-volatility. Then explain why the instructions must still be available.

Students type their answer here.

Multiple choice1 mark

A student says, “ROM is the computer's permanent storage for all photos and documents.” Which correction is best?

  • AThe statement is correct because ROM and an SSD are the same
  • BROM stores only data currently being processed
  • CROM is volatile, so it cannot store anything between sessions
  • DROM usually stores fixed firmware or control instructions; user files are normally kept in secondary storage
Written answer6 marks

Challenge: a student says, “RAM, ROM and cache are just three names for the same storage.” Evaluate this statement.

Reject or qualify the claim, then compare what each stores, whether it keeps its contents without power and how it supports the CPU.

Students type their answer here.

Closed-book review

Hide the explanations and complete these prompts from memory:

  1. A computer needs primary storage because...
  2. RAM is...
  3. RAM commonly stores...
  4. ROM is...
  5. ROM commonly stores...
  6. One example of ROM in an embedded or historic system is...
  7. ROM and secondary storage are both non-volatile, but they are not the same because...
  8. Cache helps the CPU by...
  9. One clear difference between RAM and ROM is...

Check that every answer names a purpose or characteristic, rather than saying only that something “stores things”.