Classification by capability

Perhaps the best way to classify the various types of computing device is by their intrinsic capabilities rather than their usage, implementation technology or design features. Computers can be subdivided into three main types based on capability: Single-Purpose devices that can compute only one function (e.g. The Antikythera Mechanism 87 BC, and Lord Kelvin's Tide predictor 1876), Special-Purpose devices that can compute a limited range of functions (e.g. Charles Babbage's Difference Engine No 1. 1832 and Vannevar Bush's Differential analyser 1932), and General-Purpose devices of the type used today. Historically the word computer has been used to describe all these types of machine but modern colloquial usage usually restricts the term to general-purpose machines.