What is a Two-Tier Architecture?

A two-tier architecture is where a client talks directly to a server,
with no intervening server.  It is typically used in small environments
(less than 50 users).

Advantages and Disadvantages

The advantage of the two-tier design is its simplicity. The TopLink database session that builds the two-tier architecture provides all the TopLink features in a single session type, thereby making the two-tier architecture simple to build and use.

The most important limitation of the two-tier architecture is that it is not scalable, because each client requires its own database session.