Topic Three (1.3): Introducing Fetch-Decode-Execute… Repeat and All About the Accumulator

Topics Icon.png Objectives for this topic

By the end of this topic, you should be able to:

  • describe the von Neumann Fetch-Decode-Execute cycle;
  • trace through an assembly language program;
  • describe the accumulator and its use.

You might also be able to:

  • discuss the differences between high-level and low-level languages.

Introduction Icon.png Introduction

John von Neumann brought many advances to the field of computing. With the developments of the combined memory model there came a need to formalise the way a program runs. This is known as the Fetch-Decode-Execute cycle; by following the FDE cycle, you can trace an assembly language program to identify the results.

Along with the development of the method, a number of special purpose memory modules called registers were designed and integrated into the cycle. One of the most important of these is the accumulator – you will be introduced to the use of the accumulator in this topic.

Interact Icon.png Working through your coursebook

Read pages 18—20 in your Computing Stage 9 book.

  • Read the Learn box on page 18.
  • Read the abstraction and algorithmic thinking box; consider how this topic relates to abstraction.
  • Make sure that you understand the keywords described on page 19. Add them to your cram.com Links to an external site. flashcards. 
  • Complete the Practise task on pages 18-20. You can access the worksheet here:

DOWNLOAD - Introducing the fetch decode execute cycle Download DOWNLOAD - Introducing the fetch decode execute cycle 

  • Read pages 21-25 in your Computing Stage 9 book.
  • Read the Learn box on pages 21-22.
  • Read the Computational Thinking box on page 23.
  • Make sure that you understand the keyword described on page 23. Add it to your cram.com Links to an external site. flashcards. 
  • Complete the Practise task on pages 23-25. You will need the link below:

 ACCESS - Little Man Computer (peterhigginson.co.uk) Links to an external site. 

Review Icon.png Review

Reflect upon the pages you have just covered. In your notes, summarise:

  • what you have learnt;
  • what you already knew;
  • what surprised you;
  • what you are curious to know more about.

Bridge Icon.png  Support activity for this topic

Watch this video of a more in-depth look at the cycle:

Stretch Icon.png Extension activity for this topic

Watch this video to learn a little more about the LMC: