The Stored Program Concept
John von Neumann and Alan Turing both proposed the stored program concept in separate publications in 1945.
- A program must be resident in main memory to be executed
- Machine code instructions are fetched from main memory one-at-a-time, decoded and executed in the processor.
Von Neumann Architecture
In a von Neumann machine, a single store holds both instructions and the data that they are carried out on.
A Harvard machine has a separate store for data and instructions. In the von Neumann machine, data and instructions share the same storage space and are fetched along the same bus. In the Harvard machine, throughput is quicker since there are separate stores for data and instructions and separate buses to connect them to the processor.
The term microcontroller is used to refer to a chip which contains processor, memory and IO all on a single chip. They are typically used in embedded computers (an MP3 player, in a car) and often use the Harvard architecture.