The von Neumann Architecture

The first computers were more like 'machines' - made to do one task faster than a human could.

Mathematicians like Alan Turing and John von Neumann developed the breakthrough to the computers we are surrounded by nowadays by proposing the 'stored-program' computer.

The fact that you can close Word, open Excel, then close that and watch a video on YouTube, or the way you can install any app you want on your phone - these are all different 'programs' that are 'stored' on your device.

Data and instructions are stored in the same memory in this model.

The instructions are loaded into the short term memory, and so is the data that the program will work with.

• Right now, someone could be running the Microsoft Word application which will be held in their RAM.
  

• When they open a document, that will also be held in RAM.
  

• As they type more text into the document, the data they type is ALSO held in RAM.

The same thing could be said about Excel, PowerPoint, Photoshop, Chrome, Mario Kart, etc...

This is actually quite easy to understand if you think about how your brain does things.

You have known how to add two numbers together for at least 10 years now. Let's call that the "adding" program. So if you know you're about to add something, you start thinking about it and it comes from your long-term memory (storage) into your short-term memory (RAM).

• If I ask you to add 7 and 8, your brain runs the program and you get 15.
  

• If I ask you to add 3 and 2, your brain runs the program again and you get 5.
  

Your short term memory (your RAM) was holding the 'Add' program's instructions and then it was also holding the numbers I gave you - 7, 8, 3, 2.

Data and instructions - both held in RAM.

Von Neumann stated that a computer needs a processing unit, memory, and input-output devices which are interconnected through a single, central system bus.

Every device we use nowadays follows this same rule, whether it's a Playstation, an iPhone, a laptop or a supercomputer.

Imagine you had a test paper and a separate answer sheet.

You're in the middle, with your brain.

You start off with 0 questions done. How do we complete the test?

1. Look at the question paper and read the next question

2. Work it out using your brain

3. Write the answer on the answer sheet

What's the next step?
When do you stop?

Create a Word document of notes using the web link on the next slide. It should take you to https://tinyurl.com/mtubj44y

Read through (and watch any animations) the Fetch-Decode-Execute page and the slides on Memory and Storage.

Create a good-looking document that will help you remember this sort of information. We'll print them out and stick them in our books when I'm back in.

If you email me your Word Document I can print them out in time for when I next actually see you.