The first devices facilitating the calculations
were already known in antiquity for example. "Abacus" known as early as 440 BC
The mechanical calculating machines existed for centuries.
The development of electronic devices
with no moving mechanical parts based initially
on tubes and then on transistors and integrated circuits
was real change.

Theoretical Basics

The construction of computers was possible after the discovery
of some new algorithmic ways of thinking and theoretical models
The most important are the so-called Turing Machine and Von Neumann architecture

The First Computers

As the first computers are usually considered
electronic devices like ENIAC, Colossus, ABC

The Beginnings of Software