Von Neumann

The task of entering and altering programs for the ENIAC was extremely tedious.

The programming process could be facilitated if the program could be represented in a form suitable for storing in memory alongside the data.

Then, a computer could get its instructions by reading them from memory, and a program could be set of altered by setting the values of a portion of memory.
This idea, known as the Stored-program concept, is usually attributed to the ENIAC designers, most notably the mathematician John von Neumann, who was a consultant on the ENIAC project.

In 1946, von Neumann and his colleagues began the design of a new stored-program computer, referred to as the IAS computer, at the Princeton Institute for Advanced Studies.

The IAS computer, although not completed until 1952, is the prototype of all subsequent general-purpose computers.

Figure shows the general structure of the IAS computer.

It consists of:
A main memory, which stores both data and instructions.
An arithmetic-logical unit (ALU) capable of operating on binary data.
A control unit, which interprets the instructions in memory and causes them to be executed.
Input and output (I/O) equipment operated by the control unit.