OCR · GCSE · Computer Science
Course version: J277 · Version from Sept 2022
Primary storage (memory): The need for primary storage
Primary storage is the memory the CPU accesses directly while a program runs.
Checked against the OCR J277 specification on .
- Point 1 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Primary storage is the memory the CPU accesses directly while a program runs. It is needed because the CPU can only execute instructions and process data that are held in immediately addressable memory; secondary storage such as a solid-state drive or hard disk is far slower and cannot be read directly by the CPU. Primary storage holds the currently running program's instructions, the data being processed, the operating system in use and the BIOS/firmware needed at start-up. It is volatile or non-volatile: RAM loses its contents when power is removed, whereas ROM keeps firmware permanently. Capacity and speed matter because too little memory forces swapping to slower secondary storage, reducing performance.
For example: Opening a video editor loads its code and project data into RAM so the CPU can fetch and execute instructions quickly.
What earns the marks
- Primary storage is directly accessible by the CPU, unlike secondary storage which must first be loaded into memory.
- RAM is volatile and stores currently running programs and data; ROM is non-volatile and stores fixed start-up instructions.
- Primary storage is much faster than secondary storage, so it reduces the time the CPU waits for instructions and data.
- Insufficient primary storage causes swapping or paging to secondary storage, which slows execution.
Common mistakes and how to put them right
Saying primary storage is only RAM.
Put it right by noting ROM is also primary storage because the CPU can access it directly.
Confusing primary storage with secondary storage.
Put it right by stating secondary storage is non-volatile, larger and slower, and is not directly executed by the CPU.
Claiming primary storage permanently stores all files.
Put it right by explaining RAM is volatile and files are kept in secondary storage until loaded.
Exam tips
- Link every point back to the CPU: primary storage exists so the CPU can fetch and execute instructions quickly.
- Use the terms volatile and non-volatile accurately, and name RAM and ROM as examples of primary storage.
- When asked why more RAM improves performance, explain that more programs and data fit in fast memory, reducing slow transfers from secondary storage.
Try the lesson
The start of the Primary storage (memory): The need for primary storage lesson, made from checked teaching notes for this specification point.
Have a go first
Why does a computer need primary storage?
Listen
Primary storage is the memory the CPU accesses directly while a program runs. It is needed because the CPU can only execute instructions and process data that are held in immediately addressable memory; secondary storage such as a solid-state drive or hard disk is far slower and cannot be read directly by the CPU. Primary storage holds the currently running program's instructions, the data being processed, the operating system in use and the BIOS/firmware needed at start-up. It is volatile or non-volatile: RAM loses its contents when power is removed, whereas ROM keeps firmware permanently. Capacity and speed matter because too little memory forces swapping to slower secondary storage, reducing performance. For example, opening a video editor loads its code and project data into RAM so the CPU can fetch and execute instructions quickly. A strong answer earns marks for these points. Primary storage is directly accessible by the CPU, unlike secondary storage which must first be loaded into memory. RAM is volatile and stores currently running programs and data; ROM is non-volatile and stores fixed start-up instructions. Primary storage is much faster than secondary storage, so it reduces the time the CPU waits for instructions and data. Insufficient primary storage causes swapping or paging to secondary storage, which slows execution. A common slip: Saying primary storage is only RAM. Instead, noting ROM is also primary storage because the CPU can access it directly. Exam tip: Link every point back to the CPU: primary storage exists so the CPU can fetch and execute instructions quickly.
See it
Key words
Say what each word means before you turn the card.
CPU access to instructions and data
Try answering aloud or in your head before turning the card.
Volatility and persistence
Try answering aloud or in your head before turning the card.
Speed and performance
Try answering aloud or in your head before turning the card.
Operating system and firmware start-up
Try answering aloud or in your head before turning the card.
See every definition
- CPU access to instructions and data
- Primary storage is the memory the CPU accesses directly while a program runs, because the CPU can only execute instructions and process data held in immediately addressable memory.
- Volatility and persistence
- RAM is volatile and loses its contents when power is removed, whereas ROM is non-volatile and keeps firmware permanently.
- Speed and performance
- Primary storage is much faster than secondary storage, and too little memory forces swapping to slower secondary storage, reducing performance.
- Operating system and firmware start-up
- Primary storage holds the operating system in use and the BIOS/firmware needed at start-up.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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