The three-tier architecture, also known as the three-tier model or three-tier design, is a software architecture pattern that divides an application into three distinct layers or tiers, each responsible for a specific set of functionalities. This architecture is commonly used in software development to create scalable, maintainable, and modular applications. The three tiers are:

1. Presentation Tier (User Interface Tier):

• The presentation tier is the topmost layer and is responsible for interacting with users or clients.
• It handles user interface (UI) components, such as forms, screens, and user input.
• This tier is concerned with the visual representation of the application and user interactions.
• It communicates with the underlying tiers to fetch and display data, as well as to send user requests for processing.

1. Application Tier (Logic Tier):

• The application tier, sometimes called the logic tier or business logic layer, contains the application’s core logic and functionality.
• It processes user requests from the presentation tier, performs required computations, and interacts with the data tier.
• Business rules, validation, calculations, and other application-specific logic are implemented in this tier.
• The application tier acts as an intermediary between the presentation tier and the data tier, ensuring separation of concerns.

1. Data Tier (Data Storage Tier):

• The data tier, also known as the data storage layer, is responsible for managing and storing data.
• It includes databases, file systems, and other data storage mechanisms.
• The data tier handles data retrieval, storage, and manipulation, based on the requests from the application tier.
• Separating the data tier from the other tiers allows for efficient data management and scalability.

Advantages of the Three-Tier Architecture:

1. Modularity and Scalability: Each tier can be developed and maintained independently, allowing for better modularity and easier scalability of the application.
2. Separation of Concerns: The clear separation of presentation, application logic, and data management enhances code maintainability and readability.
3. Reusability: Components in each tier can be reused across different parts of the application, leading to more efficient development.
4. Flexibility: If changes are required in one tier, it’s often possible to make adjustments without affecting the other tiers.
5. Improved Security: The separation of tiers can help enhance security by controlling access to different parts of the application.

Three-tier architecture is a foundational concept in software engineering, and it has served as the basis for more advanced architectural patterns like the Model-View-Controller (MVC), Model-View-Presenter (MVP), and Model-View-ViewModel (MVVM) patterns.