The history of computing hardware covers the developments from simple devices to aid calculation, to mechanical calculators, punched card data processing and on to modern stored-program computers . Before the 20th century, most calculations were done by humans. Early mechanical tools to help humans with digital calculations were called "calculating machines", by proprietary names, or even as they are now, calculators . The machine operator was called the computer. The first aids to computation were purely mechanical devices which required the operator to set up the initial values of an elementary arithmetic operation, then manipulate the device to obtain the result. The slide rule and, later, analog computers represented numbers in a continuous form, for instance distance along a scale, rotation of a shaft, or a voltage. Numbers could also be represented in the form of digits, automatically manipulated by a mechanical mechanism. Although this approach generall
