Fido is a simple processor simulation, designed to show the way the fetch execute cycle happens. It also shows the use of typical registers and addressing modes. It is based on von Neumann architecture, so that both program instructions and data are held in memory. Details are here. This is a simple first approach. It ignores ideas such as pipelining, multi-core and multi-processor designs.
To use Fido, either choose one of the built-in programs or write your own (you'll need to check out the instruction set). Then either single step though the code, or click 'Run' for an animation.