KS3 Computing/unattached/KS3 Computer Science/Computers
A computer is any device which can take information as input, processes it in some way and then output the results back to the user again. It doesn't have to be electronic like the computer you are reading this on. It could even be a living organism!
People have used computers since the prehistoric times. The first known device used to perform calculations were tally sticks, which at first were just notches carved into bone.