From Relays to Electronic Computers
1948: When the Program Entered Memory
Explain the practical difference between rewiring a machine and loading new instructions.
In this lesson
Lesson goals
Explain the practical difference between rewiring a machine and loading new instructions.
The idea explained
On 21 June 1948, Manchester Baby ran an electronically stored program. It was an experimental machine, not a household product, but demonstrated a powerful practical idea: fetch instructions from memory and change the task by changing stored information. Imagine a notebook holding both steps and numbers. Execution follows stored steps instead of requiring each new task to be expressed through rewiring.
Dates and milestones
- 21 June 1948: Manchester Baby’s historic program run.
Why was this a turning point?
A program became loadable and editable stored information, separating many functional changes from hardware reconstruction.
Activity: try before reading the answer
Order loading, fetching, executing and advancing instructions. Where can the task be changed?
Answer and explanation
Load first, then fetch, execute and advance or branch. Changing instructions changes the task without redesigning circuits for each program.