Tuesday, 16 May 2017

Difference between Tier and Layers

During an interview this question was asked and I was pretty sure that what ever layers we create in our code (Presentation, BLL, DLL etc) are the tiers but I was wrong.
An answer on stack overflow sums it up very well.
layer = a part of your code, if your application is a cake, this is a slice.
tier = a physical machine, a server.

Scott Hanselman also have a nice blog post on same. He says:
a "Tier" is a unit of deployment, while a "Layer" is a logical separation of responsibility within code.  You may say you have a "3-tier" system, but be running it on one laptop.  You may say your have a "3-layer" system, but have only ASP.NET pages that talk to a database. 

and then he explains about what should be there in your Presentation, BLL and DLL and what should not be there.


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