This architecture stores the program data and the instructions in the same memory unit.

The basic elements are:

• Processing unit: Contains both the arithmetic/logic unit and the processor registers.
• Control unit : Contains an instruction register and program counter.
• Memory : Storing _both_ data and instructions.
• External Mass Storage
• I/O mechanisms

The term "von Neumann architecture" has evolved to refer to any

stored-program computer in which an instruction fetch and a data operation

cannot occur at the same time (since they share a common bus). This is

referred to as the von Neumann bottleneck, which often limits the performance

of the corresponding system.[3]

Because the single bus can only access one of the two classes of memory at a

time, throughput is lower than the rate at which the CPU can work. This

seriously limits the effective processing speed when the CPU is required to

perform minimal processing on large amounts of data. The CPU is continually

forced to wait for needed data to move to or from memory. Since CPU speed and

memory size have increased much faster than the throughput between them, the

bottleneck has become more of a problem, a problem whose severity increases

with every new generation of CPU.

source

This architecture is simpler than the Harvard Architecture which includes a dedicated set of addresses to host the program instructions, and another set of addresses plus data buses for reading and writing to memory.