Single tier, Two tier and Three tier in Distributed Technology

Distributed Technology:

Distributed Technology is a concept of maintaining application logic scattered on different systems. This provides security for business calculations, resources like database, and maintanance will be easier.

Generally an Application comes with 3 parts.

1. Presentation logic (PL)
2. Business logic (BL)
3. Data storage

Arranging 3 parts of application will provide 3 types of architectures.

1. Single tier (or) Monolithic Architecture
2. Two tier
3. Three tier

1. Single tier (or) Monolithic Architecture : When the application is operated by single user it is recommended to go with single tier architecture

2. Two tier architecture : When the requirement is sharing data by set of applications, the solution will be two tier architecture.

The business logic is repeated in each client system. It requires reusability and better maintanance. The solution is maintaining Business logic with database server in the form of stored subprogram. This is called 2(1/2) tier architecture.
When it comes to enterprise level it is not recommended to maintain business logic with database server for the following reasons.

1. More burden on database, it will degrade performance of database.
2. Each client system requires clientside software of database. The company should purchase more number of clientside licenses for database. This requires more financial investment.
3. Providing database location to client system is not recommended in certain cases for security reason.
4. When the organisation is moving from one database to another database, the maintanance will not be easier. The solution is three tier architecture.

3. Three tier architecture : In three tier architecture business logic is maintained independent of client application and database. In this case client application is database independent application.

Reference:

http://codemyne.net/articles/Distributed-technology.aspx?visitid=24&type=2