Q. Describe key features of the von Neumann Architecture?

Describe key features of the von Neumann Architecture:

• The mainly basic function performed by a computer is execution of a program that involves:

-  Execution of an instruction that supplies information about an operation.

-  Data on which operation is to be performed. 

Control unit (CU) interprets each one of these instructions in addition generates respective control signals.

• Arithmetic Logic Unit (ALU) carries out arithmetic and logical Operations in special storage areas known as registers as per instructions of CU. Size of the register is one of the significant considerations in concluding processing capabilities of CPU. Register size denotes the amount of information which can be held in a register at a time for processing. Larger the register size, the faster can be the speed of processing.
• Input/ Output system which involves I/O devices allows data input and reporting of results in proper format and form. For transfer of information a computer system internally requires system interconnections. One of the interconnection structures is BUS interconnection.
• Main Memory is required in a computer to store data and the instructions at the time of Program execution. Memory to CPU is a significant data transfer path. The amount of information that can be transferred between memory and CPU depends on size of BUS connecting the two.
• It was revealed by von-Neumann that same memory can be employed for storing data and instructions. In such a case data can be treated as data on that processing can be performed whereas instructions can be treated as data that can be used for generation of control signals.
• Von Neumann machine employs stored program idea which implies that program and data are stored in same memory unit for execution. Computers before this idea used to store programs and data on separate memories. Modifying and entering these programs was too difficult as they were entered manually by plugging, unplugging and setting switches.
• In von Neumann machine execution of instructions is performed in a sequential fashion (except explicitly altered by program itself) from one instruction to next.

Figure shows fundamental structure of a conventional von Neumann machine

Figure: Structure of a Computer

Von Neumann machine has only a single path between control unit (CU) and main memory. This aspect is called as von Neumann bottleneck. Numerous other architectures have been proposed for modern computers.