What is the optimal design for a university system encompassing the following entities: students, professors, addresses, courses, departments, and grades? The design should include an Entity Relationship Model illustrating each entity with its attributes, primary and foreign keys, and the relationships between all entities should be visually represented. Considerations for storage and performance should be taken into account, as the final grade depends on the best solution, recognizing that there may be more than one correct approach.

Note: you may draw by hand, or using other tools for ER design. When done, upload your image.