What is a Tier and what tiers could be there in Architecture ?

Tier

• A logical or physical organization of components into an ordered chain of service providers and consumers.
  
• Components within a tier typically consume / provide services to their "adjacent" tiers.

Tiers in Architecture

• Client
• Web / Presentation
• Business
• Integration
• Resource

2 Tier Architecture

• A Client/Server Architecture

3/Multi Tier Architecture

• Typically has :
• Client/Presentation Tier : UI which translates results to the format understandable by user
• Business Tier : Processing, Business logic and calculations
• Database Tier : Retrieve / Store info to database