SAP R/3 is based on a 3-tier client-server architecture, which separates presentation, application, and database layers. This design provides scalability, flexibility, and better performance.

Three-Tier Architecture:

1. Presentation Layer (Client Tier)

• Interface between the user and SAP system
• Usually a SAP GUI or web browser
• Sends user input to the application server and displays output
• Example: Entering a sales order in SAP GUI

2. Application Layer (Middle Tier)

• • Core processing engine of SAP R/3
  • Handles:
    • Business logic
    • Running ABAP programs
    • Communicating with the database
    • Managing user sessions
  • Multiple application servers can run in parallel (load balancing)

• 3. Database Layer (Back-End Tier)
  • Stores all data including:
    • Business data (e.g., orders, customers)
    • Customizing settings
    • Repository objects (tables, programs, etc.)
  • Typically uses Oracle, SAP HANA, MS SQL Server, etc.

Concepts:

• Dispatcher: Manages requests in the app server.
• Work Processes: Carry out specific tasks (Dialog, Background, Update, etc.).
• Message Server: Distributes load between application servers.
• Gateway: Manages communication with external systems.