What does the three-tier client-server architecture separate?

The three-tier client-server architecture is designed to separate distinct layers within an application, specifically the presentation layer, application layer, and data layer. This separation is crucial for several reasons:

1. Modularity: By dividing the architecture into these three layers, each layer can be developed and maintained independently. This modularity helps in isolating the user interface changes from the business logic and data storage changes, thus simplifying updates and maintenance.

2. Scalability: The architecture allows for independent scaling of each layer. For instance, if there's a need for more processing power due to increased user load, additional servers can be added to the application layer without affecting the presentation or data layers.

3. Flexibility: This separation allows different technologies and frameworks to be used in each layer. For example, a web-based user interface can be developed separately from the application logic, which might be implemented in a different programming language or framework, and both can interact with a database layer regardless of its location or technology.

4. Security: Each layer can have its own security measures implemented, helping to protect sensitive data in the data layer from exposure to the client side while also securing the application logic.

This architecture is widely used in modern software