Von Neumann Machine is the basic architecture of the modern computer as it laid the foundation for same memory usage for program and data. The Von Neumann Machine consists of three main components : Main Memory C.P.U I/O devices There is already a caption As you can see the C.P.U is also sub divided into two parts : Arithmetic Logic Unit Program Control Unit This allowed the architecture designers to work on different capabilities of the C.P.U. separately. Now we have the control unit and ALU different.. We need to get some instructions to work and some data to work upon. We can get all that data and instructions from Common Memory. Since the processing is fast compared to data retrieval. We need some device to hold data and instructions from memory for processing at the same speed the Processor works... Thus Registers came into play... A processor register is a quickly accessible location available to a digital processor 's central processin