Classification according to ability
One of the easiest ways to classify different types of computing devices is the determination of their abilities. All calculators can thus be attributed to one of three types:
Specialized devices, able to perform only one function (eg, Antikythera mechanisms 87 BCE. Oe. Filar or forecaster William Thomson, 1876);
Special-purpose devices that can perform a limited range of functions (the first difference engine of Charles Babbage and a variety of differential analyzers);
General-purpose devices that are used today. Name of computer used, as a rule, to machines for general use.
Modern general-purpose computer
When considering modern computers the most important feature distinguishing them from early computing devices, is that with appropriate programming, any computer can emulate the behavior of any other (although this option and restricted, for example, the capacity of the storage or the difference in speed). Thus, it is assumed that current machines can emulate any computing device of the future that can ever be created. In a sense, this threshold ability is useful to distinguish between general-purpose computers and devices for special purposes. Definition of "general-purpose computer" can be formalized in the requirement that a particular computer was capable of imitating the behavior of a universal Turing machine. The first computer that meets this condition is considered to be machine Z3, created by German engineer Konrad Zuse in 1941 (proof of this fact was held in 1998).