What is the role of three-tier architecture and why is it used in system development?

The three-tier architecture divides an application into three logical layers:

1. Presentation Layer — responsible for user interaction (UI).
2. Business Logic Layer — implements business rules and data processing.
3. Data Access Layer — works with databases or other storage.

This separation allows:

• Improved support and scalability of the code.
• Easier testing of each layer separately.
• Increased reuse of components.
• Division of responsibilities among developers.

Example: in C#, you can have separate projects or folders for UI (e.g., WinForms or ASP.NET), business logic (classes with processing methods), and data access (Entity Framework, ADO.NET).