Source : Free On-Line Dictionary of Computing

von Neumann architecture
     
         A computer {architecture}
        conceived by mathematician {John von Neumann}, which forms the
        core of nearly every computer system in use today (regardless
        of size).  In contrast to a {Turing machine}, a von Neumann
        machine has a {random-access memory} (RAM) which means that
        each successive operation can read or write any memory
        location, independent of the location accessed by the previous
        operation.
     
        A von Neumann machine also has a {central processing unit}
        (CPU) with one or more {registers} that hold data that are
        being operated on.  The CPU has a set of built-in operations
        (its {instruction set}) that is far richer than with the
        Turing machine, e.g. adding two {binary} {integers}, or
        branching to another part of a program if the binary integer
        in some register is equal to zero ({conditional branch}).
     
        The CPU can interpret the contents of memory either as
        instructions or as data according to the {fetch-execute
        cycle}.
     
        Von Neumann considered {parallel computers} but recognized the
        problems of construction and hence settled for a sequential
        system.  For this reason, parallel computers are sometimes
        referred to as non-von Neumann architectures.
     
        A von Neumann machine can compute the same class of functions
        as a universal {Turing machine}.
     
        [Reference?  Was von Neumann's design, unlike Turing's,
        originally intended for physical implementation?  How did they
        influence each other?]
     
        {(http://www.salem.mass.edu/~tevans/VonNeuma.htm)}.
     
        (2003-05-16)