In a two-tier architecture, the client application constitutes the first tier, directly interacting with the database or server as the second tier. This setup manages user interfaces and application logic on the client’s side, while the database system is stored on the server side. The absence of an intermediate layer between the client and the server is why it is named a two-tier architecture. A three-tier architecture would include another separate layer, typically the business logic, which is not mentioned in the scenario.