What is the key innovation of the Analytical Engine?

Charles Babbage designed the Analytical Engine in the nineteenth century as the successor to his earlier Difference Engine. What set the Analytical Engine apart from earlier calculating machines was that it was designed with two separate functional parts: a "mill" that carried out the arithmetic, corresponding to what would later be called a processing unit, and a "store" that held numbers and the results of calculations for later use, corresponding to what would later be called memory.

This separation between a unit that performs calculations and a unit that stores data and intermediate results for reuse is what made the Analytical Engine a genuinely programmable, general-purpose machine rather than a fixed calculator, and it is why historians of computing regard the store, or memory unit, as its key innovation. The Analytical Engine did use punched cards for input, borrowed from the Jacquard loom, but that idea already existed before Babbage applied it to his machine, so it was an adopted feature rather than the engine's own key innovation. It was not steam-powered in practice, and the concept of a distinct central processing unit as a named component came much later in computing history.

Examination reminder: the Analytical Engine's lasting significance in computing history rests on its store, the memory unit that let it retain data and results, marking it as a forerunner of the modern computer.