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Discussion on: What is a 3-tier application?

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Ian bradbury

There are many ways you could answer this question.

Really the answer is how many layers - or tiers - of responsibility are there. It is not uncommon to find 4 or more tier applications.

3 tiers : Client (ie Browser), web server, database
3 tiers : Web server, application server, database

Web server talks to the application server. The web server is only responsible for receiving request and dispatching responses.
The application server is only responsible for accepting and processing requests, during which is might talk to a database.

Etc etc you can se where this is going.

The point is that by seperating responsibility you can focus each resource so that it is excellent at doing that one thing - securely and speedily.