What is SAP R/3 Architecture?

As name suggests SAP, R/3 is a three-layered architecture as follows

• Presentation 
• Application
• Database

Which means Real-time, 3-tier architecture.

Presentation layer:

The Presentation layer is the first and top layer of the system. It contains the software components that make up the SAPGUI (graphical user interface). An interface, which connects the system (application layer where application installed) and the end user (from GUI) to perform transactions. Each end user system has a GUI application running in their systems. If there are 100 end users in an organization, all the end users will be accessing SAP through a GUI installed in their systems. Thus, the R/3 System uses the SAPGUI to provide an intuitive graphical user interface for entering and displaying data. 

The SAP front-end s/w run either on the same computer or on different computers provided for that purpose. User’s input will be accepted by the SAP GUI and forwarded to the SAP dispatcher for further processing of the user request. The dispatcher coordinates the information exchange between the SAPGUI (front-end) and the work processes (contained in system) (see in Application layer down).

Application layer:

The Application Layer is the middle layer of R/3 architecture. This layer consists of the application. It performs all transactions of the end user in this layer. Application server contains a set of services used to run the R/3 System (discussed in previous one) Instance and types
With this layer, we can process data, communicate and retrieve or store data from the database layer (AKA DB).

An application in the Application Layer consists of five components.

• Dispatcher
• Gateway
• Buffering
• Work Process (WP)
• Message

Continue with next topic to know about this.

Database layer:

The database layer, containing all the data of an R/3 system or applications installed in the system.

For example:

We are aware that the system contains of applications installed on it and consists of program code, screen definitions; menus, function modules and other components installed. All this information and data will be stored under database layer. Thus, the database contains the control and customizing data that determines how R/3 System runs. These are stored in a special section of the database called the R/3 Repository, and are accordingly called repository objects.