A computer is an electronic mechanical device designed to accept input and store data, process them and produce some output result under the direction of stored instructions.

Why we call it computer unless calculator?

There is a basic difference between the computer and the calculator because computers accept any data like text or number but calculator accepts only numbers.Computers remember any amount of data as and whenever we need. But calculator remember it for less time. The calculator only calculate numbers but a computer can calculate or manipulate both text , graphics and numbers.

The word computer comes from the word "compute" which means to calculate. Therefore a computer is normally considered to be a calculating device, which can perform arithemetic operation at a very high speed.