1. Client/Server Architecture

2. Advent of Client/Server Technology
In systems centralised around mainframe, a no. of dumb terminals used to be connected to a powerful server, which performed all the processing
It became increasingly difficult to keep up pace with changing scenarios (business rules, technologies etc.) as modifying these systems was a time consuming activity and besides affected all the users

3. Advent of Client/Server Technology
With the advent of PCs, the processing could be distributed between client and server, which accrued several benefits
A powerful Graphical User Interface (GUI) could be provided to the user instead of Character based interface, which was user-friendly
The processing could be distributed between client and server, thus taking some load off the server

4. Advent of Client/Server Technology
Improved information access
Increased productivity
Quick reponse to changing market place
Rapid application development

5. The Tiers
Applications can be logically distributed into several layers, each of which is known as a Tier
Windows DNA refers to these tiers as -
User Services
Business Services
Data Services

6. Two-Tier Architecture
In a Two-Tier Architecture the applications are mostly divided into a user-services tier and a data-services tier
The application logic resides either in the user interface or on the server, producing two models:
Fat Client (UserInterface + Business Logic on client & database logic on the server)
Fat Server (User Interface logic on client & business+database logic on server)

7. Client-Server Models Distributed Presentation Remote Presentation
Distributed Logic
Remote Data
Distributed Data

8. Client-Server Models 1 2 3 4 5 Client Server Network D D D D D BL BL
EUD D BL BL BL
EUD
EUD
EUD
EUD
EUD 1 2 3 4 5
Client

9. Three-Tier Architecture
In a three tier architecture the business services are assigned a separate tier – called middle tier and is handled by middleware like MTS and IIS

10. Three-Tier Architecture

11. From Two-Tier to N-Tier