Difference between three tier vs. n-tier

Question

I just came across the following sentence:

As the industry has moved from a three tier model to n-tier models, the object relational impedance mismatch

Answer 1

If we looked at tiers like being layers of a cake; each layer would have it's own ingredients and do it's own things. The tiers of each application interact with only the tier above it, or below it.

3-tier means the cake has 3 layers. Usually it's data at the bottom, then an application logic tier (PHP/ruby/etc), and then a presentation tier at the top (html)

Having an n-tier architecture means you design something multiple layers layer to it. The number of layers you have will depend on how you decide to make it.

It seems to make a lot more sense with larger, or web applications.

I usually end up with a 5 tier application. Each tier can only interact with the one above it or below it. This can provide fantastic extensibility and standardization across your application.

Client Tier

Web Browser

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Presentation Tier

Render the HTML - Coldfusion/Flash/Ruby/PHP,etc.

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Business Logic Tier

Run the processes and calculations as needed - Coldfusion/Flash/Ruby/PHP,etc.

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Data Integration Tier

(Queries from my Development Language, Stored Procedures, etc.)

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Data Tier

(Database - MySQL, etc)