VON Neumann Architecture:

Before answering what is the difference between the Von Neumann and Harvard Architecture lets see what are their definitions. VON Neumann is a computer architecture that was described by mathematician and physicist John Von Neumann. He gave his design in 1945. This is an old architecture and is not entertained today.

The key elements of von Neumann architecture are instructions are fetched from memory one at a time and in order the processor decodes and executes an instruction, before cycling around to fetch the next instruction. the cycle continues until no more instructions are available.

Same physical memory address is used for instructions and data.

Its block diagram is given as:

Harvard Architecture:

Harvard architecture is newer version of these architects, and it is widely used today. As it has a single path used for all its components. That’s make it more compatible for everyday use.

Separate physical memory address is used for instructions and data.

The Harvard architecture stores machine instructions and data in separate memory units that are connected by different busses. In this case, there are at least two memory address spaces to work with, so there is a memory register for machine instructions and another memory register for data.

Its block diagram is given as:

What are the Major Differences Between Von Neumann Architecture and Harvard Architecture?

Von Neumann Architecture	Harvard Architecture
It is ancient computer architecture based on stored program computer concept.	It is modern computer architecture based on Harvard Mark I relay based model.
Same physical memory address is used for instructions and data.	Separate physical memory address is used for instructions and data.
There is common bus for data and instruction transfer.	Separate buses are used for transferring data and instruction.
Two clock cycles are required to execute single instruction.	An instruction is executed in a single cycle.
It is cheaper in cost.	It is costly than Von Neumann Architecture.
CPU cannot access instructions and read/write at the same time.	CPU can access instructions and read/write at the same time.
It is used in personal computers and small computers.	It is used in micro controllers and signal processing.
Speed of execution is faster because the processor fetches data and instructions simultaneously	Speed of execution is slower since it cannot fetch the data and instructions at the same time.
It results in wastage of space since if the space is left in the data memory then the instructions memory cannot use the space of the data memory and vice-versa.	Space is not wasted because the space of the data memory can be utilized by the instructions memory and vice-versa.
Controlling becomes complex since data and instructions are to be fetched simultaneously.	Controlling becomes simpler since either data or instructions are to be fetched at a time
It requires more hardware since it will be requiring separate data and address bus for each memory.	In contrast to the Harvard architecture, this requires less hardware since only a common memory needs to be reached.
In Harvard architecture, the CPU is connected with both the data memory (RAM) and program memory (ROM), separately.	In contrast to the Harvard architecture, this requires less hardware since only a common memory needs to be reached.
This requires more space.	This requires less space.

Also read here

https://eevibes.com/computing/what-are-the-challenges-in-embedded-systems-design/

What are the Challenges in Embedded Systems Design?