1. World’s first programmable computer – Colossus
One of the world’s first programmable electronic digital computers
It was built in 1943 at Bletchley Park in the U.K, to help break codes during WW2.
Problem / Limitation
The machine was pre-built to perform a specific task and the data was fed into the machine
This computer could not store programs in its memory, only data. Instructions were carried out one at a time using switches.
It had to be rebuilt, using switches and patch cables, each time a new program was needed!
Imitation Game – Alan Turing

2. Recap
Before 1945, computers were analogue and were essentially pre programmed machines that had one purpose. They could not be reprogrammed.
Think of a calculator. This cannot be reprogrammed!
This meant that computers would be set up with wires and switches to perform a specific task. They would need to be rewired if they were required to perform a different task.
Rewiring a computer to could take weeks. Imagine having to wait 3 weeks to be able to reprogram your Xbox to play a different game!

3. John von Neumann
John was a gifted mathematician and computer scientist.
He wondered if it would be possible to create a computer that could be easily reprogrammed to perform different tasks.
John wanted to create a “universal computer” that could be programmed to perform different tasks.
In theory, this meant that engineers could spend less time setting up machines and instead spend their time creating the programs/instructions!

4. The “Stored Program Concept”
In 1945 John “cracked it!”.
He designed a computer architecture in which data and programs are both stored in the computer’s memory.
A computer built with this architecture is easier to reprogram, because you can input a new program into memory whenever you wanted to perform a different task.
The “Stored Program Concept” is the fundamental design concept behind all modern computer systems.
The processor fetches and executes the data and programs
Data and programs are stored in memory.

5. Recap
John von Neumann created of a way of making computers reprogrammable, meaning one computer could be reprogrammed to carry out different tasks.
This was known as the stored program concept - which described computer systems in which the data and programs are both stored in the computer’s memory.
John’s plan was to have separate roles for the processor and memory.
Memory would store the programs and data
The processor would fetch both the programs from memory and execute the instructions with the data.