Explain van neumann architecture of computer system?

John Von Neumann's: One shared memory for instructions (program) and data with one data bus and one address bus between processor and memory. Instructions and data have to be fetched in sequential order (known as the Von Neumann Bottleneck), limiting the operation bandwidth. Its design is simpler than that of the Harvard architecture. It is mostly used to interface to external memory.
explain correctly what is von neumann concept?
an automatic programmable computer using a single shared common memory for storing both instructions and data.

This is in contrast to Harvard Architecture, which is an automatic programmable computer using two physically separate memories for storing instructions and data.

Most modern computers use a mixture of both: the CPU itself is Harvard, getting instructions and data from two physically separate caches; but the system as a whole is von Neumann, loading both caches from a single common shared memory.