The most basic definition of a computer is a programmable machine that is able to respond to a set of instructions and be able to execute computations based on the instructions it has been fed.
The computer’s capability to use instructions (or programs) and execute it to perform a set of steps and processes is its biggest difference from simpler machines like mechanical calculators. Even though both computers and calculators make computations, a calculator is different in that it will only respond to immediate input. But modern calculators are actually taking the form of computers because it now has programs installed that help in performing more complex computations or tasks.
Computers come in many sizes – from the ultra compact computers to those that are truly large. The speed of computers also varies. There are computers that take a lot of time to finish the simplest of calculations, while there are super computers that are able to do millions of computations in just a second. But in theory, all computers are equal in that they will all be able to do the same thing.
During the infancy of computers, these machines were quite huge. In fact, the first computers would require a lot of space and a lot of power that their functions were just limited to a number of tasks.
But because of advances in technology, computers started shrinking and the energy needed by these machines also drastically dropped. This was a pivotal moment that allowed computers to start becoming a useful tool in a great number of tasks.