In a two-tier database model, what separates the database from the application?

In a two-tier database model, the architecture consists of a client-side that interacts directly with the database server. The correct choice emphasizes the role of the client workstation, which serves as the interface where users input data and receive information. The client application executes requests, sends them to the database server, and presents results back to the user.

This model is characterized by a direct communication line between the client and the database server, where the client handles presentation and certain application logic while the server manages the data storage and retrieval.

The other options relate to components typically found in computer networking or system architecture but do not accurately represent the division between application and database. The server is where the database resides, not a separating entity; the router facilitates communication but does not distinguish the two tiers directly; and the hard drive is a physical storage medium for data rather than a component that separates application logic from database management.