Harvard Architecture Vs Von Neumann Architecture

Generally there are two types of architecture for personal computers or desktop computers. Most desktop computers use von Neumann architecture, where programs and data share a single memory area that is accessed over a common bus. This scheme works well for general use computers but may not be of particular advantage for microcontrollers. That's why the PIC microcontroller uses Harvard architecture. This architecture design uses separate memory areas and buses for data and programs.

For Harvard architecture the instruction bus is allowed to be a different width than the data bus. So, an instruction can be fetched in a single clock cycle because the instruction bus can be custom tailored. The last instruction can be executed by cpu while the next one is being fetched, all while data memory is simultaneously being accessed.