twotier

Twotier, in computing and information systems, refers to a two-layer software architecture commonly known as two-tier client–server architecture. In this pattern, the user interface and presentation logic run on a client (the first tier), while the data storage and management functions run on a separate database server (the second tier). There is typically direct communication between the client and the database server, with little or no intermediary application server.

Key characteristics include direct data access from the client to the database, simpler deployment for small environments, and potentially lower development time for straightforward applications. The approach is often implemented using standard database drivers and protocols (for example, ODBC or JDBC), allowing client applications to issue queries and commands directly to the database.

Common use cases are small to mid-sized applications, desktop or local-network deployments, and scenarios where rapid development and minimal infrastructure are priorities. Two-tier designs can offer low latency for simple operations and straightforward data models, but they also present notable drawbacks.

Limitations and considerations include scalability concerns, as the database server bears the load of multiple clients and their queries; security risks associated with exposing the database to client machines; and maintenance challenges as business logic spreads across clients rather than centralized. As organizations grow, many migrate to three-tier or multi-tier architectures that introduce intermediary application servers to improve scalability, security, and manageability. Despite this, two-tier architectures remain in use for small-scale and legacy systems.