von Neumann architecture
von Neumann machine

    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?]

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

   (2003-05-16)