Three-tier distribution architecture discusses partitioning application functionality into three tiers: front-end clients, domain or application servers, and a storage and DB-server. Four Layer Architecture addresses how the objects in your system as a whole can be organized to best separate concerns and prepare you for distribution and reuse.
Phase-in tiers shows how systems using a four-layer architecture can be built initially for a two-tier architecture, and then moved to a three-tier architecture over time. Trim client demonstrates how the objects in a four layer architecture can be best distributed into the tiers of a two or three tier architecture.
Specialized Application Servers guides the process of dividing the middle layer into several application servers. Abstract Database Interface makes the application portable to different database platforms. ORB Proxy for Database Object deals with the integration of the often incompatible worlds of object brokers and object databases. Automatic Object Locks liberates developers from the tedious and error-prone work of manually locking and unlocking database objects. Shared DB Connections applies to the cases where it is necessary to have more simultaneous users than the number of connections the database servers will accept. Thread-Based Concurrency Management shows how concurrency control can be implemented in application servers when database locks can no longer be used to synchronize the clients.
Described by Kyle Brown http://www.ksc.com/article1.htm) and http://members.aol.com/kgb1001001/Articles/threetier/threetier.htm