Block structure and point-by-point structure are two ways to organize a compare and contrast essay that describes the relationship between two subjects: 

A.   Block structure

In this method, you discuss all aspects of one subject in the first paragraph, then do the same for the other subject. This method is good for showing how something new compares to something more traditional and can help readers understand and agree with your proposal. Block structure essays can be shorter and less detailed than point-by-point essays, but they can also be more challenging to discuss. 

B.    Point-by-point structure

In this method, you examine one aspect of comparison in each paragraph, usually alternating between the two subjects. This method allows you to emphasize similarities and differences as you go and can help you develop your ideas about the subjects. Point-by-point essays are generally preferred for college-level writing and can be longer and more detailed than block structure essays.