2tier

2tier, typically written as two-tier or 2-tier, refers to a category of client-server architectures in which an application is divided into two layers: a presentation layer on the client and a data layer on a central server. In a classic 2tier setup, the client handles the user interface and may include some application logic, while the server manages data storage, retrieval, and integrity. Communication often occurs directly between the client and the database server, using a database protocol or a lightweight data access layer.

This design contrasts with three-tier or multi-tier architectures, where an intermediate application server handles business logic and data access, providing a separate layer between the client and the data store. The two-tier model can be implemented with various combinations, such as a thick client that connects directly to a database or a thin client that delegates some tasks to embedded logic on the client.

Advantages of a two-tier approach include simplicity, lower latency for small numbers of users, and potentially reduced infrastructure costs. It can be practical for small organizations, desktop applications, or environments where the data layer is centralized and access patterns are straightforward.

Disadvantages include scalability challenges as user counts grow, tight coupling between the client and the data store, and heightened security and maintenance risks from exposing the database to clients. In modern systems, two-tier architectures are often supplanted by tiered designs or service-oriented and cloud-based architectures, though they remain in use for specific, tightly controlled, or legacy scenarios.