3. Features of a Von Neumann architecture

The illustration above shows the essential features of the Von Neumann or stored-program architecture.

Memory

The computer will have memory that can hold both data and also the program processing that data. In modern computers this memory is RAM.

Control Unit

The control unit will manage the process of moving data and program into and out of memory and also deal with carrying out (executing) program instructions - one at a time. This includes the idea of a 'register' to hold intermediate values. In the illustration above, the 'accumulator' is one such register.

The 'one-at-a-time' phrase means that the von neumann architecture is a sequential processing machine.

Input - Output

This architecture allows for the idea that a person needs to interact with the machine and so there needs to be an input and output facility.

Arithmetic Logic Unit

This part of the architecture is solely involved with carrying out calculations upon the data. All the usual Add, Multiply, Divide and Subtract calculations will be available but also data comparisons such as 'Greater Than', 'Less Than', 'Equal To' will be available.

Bus

Notice the arrows between components? This implies that information should flow between various parts of the computer. In a modern computer built to the Von Neumann architecture, information passes back and forth along a 'bus'. There are buses to identify locations in memory - an 'address bus'

And there are buses to allow the flow of data and program instructions - a 'data bus', along with a control bus to handle operations.

Conclusion

The Von Neumann architecture has been incredibly successful, with most modern computers following the idea. You will find the CPU chip of a personal computer holding a control unit and the arithmetic logic unit (along with some local memory) and the main memory is in the form of RAM sticks located on the motherboard.

But there are some basic problems with it. And because of these problems, other architectures have been developed. These alternatives will be discussed later.