Hi singh jee

Some more points to clear the difference between Destop, client server, & Web based applications:

Desktop application:
1. Application runs in single memory (Front end and Back end in one place)
2. Single user only

Client/Server application:
1. Application runs in two or more machines
2. Application is a menu-driven
3. Connected mode (connection exists always until logout)
4. Limited number of users
5. Less number of network issues when compared to web app.

Web application:
1. Application runs in two or more machines
2. URL-driven
3. Disconnected mode (state less)
4. Unlimited number of users
5. Many issues like hardware compatibility, browser compatibility, version compatibility, security issues, performance issues etc

Desktop application runs on personal computers and work stations, so when you test the desktop application you are focusing on a specific environment. You will test complete application broadly in categories like GUI, functionality, Load, and backend .
client server application you have two different components to test. Application is loaded on server machine while the application exe on every client machine. You will test broadly in categories like, GUI on both sides, functionality, Load, client-server interaction, backend. This environment is mostly used in Intranet networks. You are aware of number of clients and servers and their locations in the test scenario.
Web application is a bit different and complex to test as tester don’t have that much control over the application. Application is loaded on the server whose location may or may not be known and no exe is installed on the client machine, you have to test it on different web browsers. Web applications are supposed to be tested on different browsers and OS platforms so broadly Web application is tested mainly for browser compatibility and operating system compatibility, error handling, static pages, backend testing and load testing.