At Pocket-Guides.net a computer is a machine which manipulates data according to a list of instructions. Computers take numerous physical forms. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers. Modern computers are based on comparatively tiny integrated circuits and are millions to billions of times more capable while occupying a fraction of the space. Today, simple computers may be made small enough to fit into a wrist watch and be powered from a watch battery. However, the most common form of computer in use today is by far the embedded computer. The ability to store and execute lists of instructions called programs makes computers extremely versatile and distinguishes them from calculators.