Contrary to popular belief, computers existed from antiquity. Any tool used for calculation could be referred to as a computer. The earliest computers were tally sticks in use since around 20,000 BC. Mechanical analog computers started appearing in first century and were used in medieval era for astronomical calculations. In World War II, mechanical analog computers were used for specialized military applications. During this time the first electronic digital computers were developed. Originally they were the size of a large room, consuming as much power as several hundred modern personal computers (PCs).[1]