Any computer architecture in which the underlying model of computation is different from what has come to be called the standard von Neumann model (see von Neumann machine). A non von Neumann machine may thus be without the concept of sequential flow of control (i.e. without any register corresponding to a “program counter” that indicates the current point that has been reached in execution of a program) and/or without the concept of a variable (i.e. without “named” storage locations in which a value may be stored and subsequently referenced or changed).
Examples of non von Neumann machines are the dataflow machines and the reduction machines. In both of these cases there is a high degree of parallelism, and instead of variables there are immutable bindings between names and constant values.
Note that the term non von Neumann is usually reserved for machines that represent a radical departure from the von Neumann model, and is therefore not normally applied to multiprocessor or multicomputer architectures, which effectively offer a set of cooperating von Neumann machines.