Three Tier Architecture and Three Layer Architecture - .Net Framework

Difference Between Three Tier And Three Layer Architecture?

In the previous article I explained about C# - Design Patterns in Software Development Process? In this article I will explain the difference between Three Tier And Three Layer Architecture?

Three Layer Architecture

Layer indicates logical separation of code or components, logical layers help you organize your code better such as having distinct namespaces and classes for the Database Access Layer, Business Logic Layer and User Interface Layer. There are following benefits of the layered architecture:

• Abstraction
• Isolation
• Manageability
• Performance
• Re-usability
• Testability

3-tier Architecture

Tier indicates a physical separation of components, which may mean different assemblies such as DLL, EXE, etc. on the same server or multiple servers. Specifically, tiers are places where layers are deployed and where layers run. There are following benefits of the tier architecture:

• Maintainability: Because each tier is independent of the other tiers, updates or changes can be carried out without affecting the application as a whole.

• Scalability: This is because tiers are based on the deployment of layers, scaling out an application is reasonably straightforward.

• Flexibility: This is because each tier can be managed or scaled independently, flexibility is increased.

• Availability: Applications can exploit the modular architecture of enabling systems using easily scalable components, which increases availability.

Difference between a multi-layer and multi-tier applications

When we talk about multi-layer, we usually mean an application broken down into multiple layers such as a Database Layer, a Business Layer, and a User-interface layer. All of these layers may be separate assemblies. 

For example, UI layer may have ASP.Net pages, Business layer may be BL.dll and the data layer may be Db.dll. However, these all assemblies usually reside on the same machine where the application runs.

When we talk about multi-tier, these assemblies reside on separate physical machines. In other words, there will be more than one physical machine involved in multi-tier application.

N-tier Example:

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