What's the difference between "Layers" and "Tiers"?

Question

What's the difference between "Layers" and "Tiers"?

Answer 1

Read Scott Hanselman's post on the issue: http://www.hanselman.com/blog/AReminderOnThreeMultiTierLayerArchitectureDesignBroughtToYouByMyLateNightFrustrations.aspx

Remember though, that in "Scott World" (which is hopefully your world also :) ) 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. There's power in precision, friends.

Answer 2

I use layers to describe the architect or technology stack within a component of my solutions. I use tiers to logically group those components typically when network or interprocess communication is involved.

Answer 3

I've found a definition that says that Layers are a logical separation and tiers are a physical separation.

Answer 4

Logical layers are merely a way of organizing your code. Typical layers include Presentation, Business and Data – the same as the traditional 3-tier model. But when we’re talking about layers, we’re only talking about logical organization of code. In no way is it implied that these layers might run on different computers or in different processes on a single computer or even in a single process on a single computer. All we are doing is discussing a way of organizing a code into a set of layers defined by specific function.

Physical tiers however, are only about where the code runs. Specifically, tiers are places where layers are deployed and where layers run. In other words, tiers are the physical deployment of layers.

Source: Rockford Lhotka, Should all apps be n-tier?

Answer 5

physical separation as Tier and (Definitely) logical separation as layer