Primary Storage (Cambridge (CIE) IGCSE Computer Science)

Revision Note

James Woodhouse

Written by: James Woodhouse

Reviewed by: Lucy Kirkham

Primary Storage

  • Primary storage is directly accessed by the CPU

  • Computer systems need both primary and secondary storage to operate

  • Both types of storage play a crucial role in the operation of a computer system

  • A quick comparison of primary and secondary storage shows:

Primary

Secondary

Volatile (with the exception of ROM)

Non-volatile

Small capacity

Large capacity

Why do you need primary storage?

  • A computer needs primary storage because access times are considerably faster than secondary

  • This means the time taken to complete operations such as the Fetch-Execute Cycle is dramatically reduced 

  • Primary storage holds the data and instructions that the CPU needs to access whilst the computer is turned on

  • Due to the fast access times, primary storage is used as short-term, working memory, in hardware that is directly connected to the CPU such as RAM, and components that reside inside the CPU such as Cache and Registers

  • Performance of primary storage means a much higher cost which limits the amount that is used

  • For example, RAM is commonly purchased in 16 or 32 gigabytes whereas secondary storage such as a hard drive is in terabytes

RAM

What is RAM?

  • RAM (Random Access Memory) is primary storage that is directly connected to the CPU and holds the data and instructions that are currently in use

  • RAM is volatile which means the contents of RAM are lost when the power is turned off

  • For the CPU to access the data and instructions they must be copied from secondary storage

  • RAM is very fast working memory, much faster than secondary storage

  • RAM is read/write which means data can be read from and written to

  • In comparison to ROM, it has a much larger capacity

Examiner Tips and Tricks

Just knowing what RAM is and what it stores is not enough, you must be able to apply your understanding of RAM to real world contexts where RAM is a component, e.g. TVs, game consoles and other smart devices

Worked Example

A smart television allows the user to search the Internet and watch videos online.

The smart television uses RAM

Give two examples of data that the smart television could store in RAM [2]

How to answer this question

  • Think about the main function of a smart television, watch channels, use apps to stream content and browse the web etc

  • For each function, try to think of what data would have to be in the RAM whilst you were actually doing it (in use!

Possible answers

  • Current channel being watched

  • Current volume

  • Current video/file/tv program being watched

  • Web browser/applications that are running

  • Data being downloaded/buffered

Examiner Tips and Tricks

Examiners will accept anything reasonable when answering these style of questions BUT brand names will not be be awarded without giving an example 

ROM

What is ROM?

  • ROM (Read Only Memory) is primary storage that holds the first instructions a computer needs to start up (Bootstrap)

  • ROM contains the BIOS (Basic Input Output System)

  • ROM is a small memory chip located on the computers motherboard

  • ROM is fast memory, much faster than secondary storage but slower than RAM

  • ROM is non-volatile which means the contents of ROM are not lost when the power is turned off

  • ROM is read only which means data can only be read from

  • In comparison to RAM, it has a much smaller capacity

Examiner Tips and Tricks

RAM & ROM are examples of primary storage, they can be referred to as Main Memory or Primary Memory in the exam

Worked Example

Quinn has 512 kilobytes of ROM and 16 gigabytes of RAM in her computer

  1. Describe the purpose of the ROM in Quinn's computer [2]

  2. Describe the purpose of the RAM in Quinn's computer [2]

Answer

  1. ROM

    • Store start-up instructions/bootstrap

    • Used to start the computer

  2. RAM

    • Stores the parts of the OS / programs that are running

    • Stores data currently in use

    • ...for access by the CPU

Guidance

  • Do not confuse the purpose with characteristics, describe what it does, not what it is 

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James Woodhouse

Author: James Woodhouse

Expertise: Computer Science

James graduated from the University of Sunderland with a degree in ICT and Computing education. He has over 14 years of experience both teaching and leading in Computer Science, specialising in teaching GCSE and A-level. James has held various leadership roles, including Head of Computer Science and coordinator positions for Key Stage 3 and Key Stage 4. James has a keen interest in networking security and technologies aimed at preventing security breaches.

Lucy Kirkham

Author: Lucy Kirkham

Expertise: Head of STEM

Lucy has been a passionate Maths teacher for over 12 years, teaching maths across the UK and abroad helping to engage, interest and develop confidence in the subject at all levels.Working as a Head of Department and then Director of Maths, Lucy has advised schools and academy trusts in both Scotland and the East Midlands, where her role was to support and coach teachers to improve Maths teaching for all.