What is the difference between two tier and three architecture?

Question

I'm using JDBC in my application with business logic(client). This JDBC connects to the database which is in another machine(server). In this case, my JDBC directly connects with the database and stores & retrieves data. This is TWO-TIER architecture right?

In another application, for example servlet programming, I'm simply having browser in my client machine which is the presentation Layer(Client tier). Let me consider my business logic as Application Layer(Second tier) and database as Data layer(Third tier). Still I'm using JDBC to connect my application(business logic) with the database. Second and third tiers reside at server now.

By the above example, in three tier architecture a browser only added additionally and kept my business logic at server. I'm not feeling any performance difference other than these. If I'm wrong please correct me and explain me the exact architecture of 2-tier and 3-tier with other examples. Thanks in advance dear friends.

Answer 1

What you say is right.

1. You first example is two-tier.
2. The second example is three-tier.

A three-tier architecture can represent an important performance gain if the link between browser and server is slower than the link between server and DBMS. This is because usually the business logic needs to make several calls to the DBMS and/or present to the user only a small part of the information returned by the DBMS. Having the business logic in the client while having a slow connection to the DBMS would represent an important performance penalty.

In a typical web scenario, the connection between client and server is usually several times slower than the connection between server and DBMS, and there is your performance gain.