von Neumann architecture

von Neumann architecture

(architecture, computability)A computer architectureconceived by mathematician John von Neumann, which forms thecore of nearly every computer system in use today (regardlessof size). In contrast to a Turing machine, a von Neumannmachine has a random-access memory (RAM) which means thateach successive operation can read or write any memorylocation, independent of the location accessed by the previousoperation.

A von Neumann machine also has a central processing unit(CPU) with one or more registers that hold data that arebeing operated on. The CPU has a set of built-in operations(its instruction set) that is far richer than with theTuring machine, e.g. adding two binary integers, orbranching to another part of a program if the binary integerin some register is equal to zero (conditional branch).

The CPU can interpret the contents of memory either asinstructions or as data according to the fetch-execute cycle.

Von Neumann considered parallel computers but recognized theproblems of construction and hence settled for a sequentialsystem. For this reason, parallel computers are sometimesreferred to as non-von Neumann architectures.

A von Neumann machine can compute the same class of functionsas a universal Turing machine.

http://salem.mass.edu/~tevans/VonNeuma.htm.

von Neumann architecture

Hungarian-born John von Neumann (1903-1957), an internationally renowned mathematician, promoted a theoretical design for a computer in the 1940s. He envisioned the stored program concept, whereby instructions would be fed into the computer's internal memory (RAM), and they would be executed to process the data that were also fed into the same memory. Contrast with Harvard architecture.

John Luis von Neumann
Von Neumann's name is perhaps mentioned more than any other early computer pioneer because the subject of sequential operations versus parallel operations is often discussed. (Image courtesy of The Computer History Museum, www.computerhistory.org)