What are the 3 Layer in SAP R/3 architecture?

They are:-

• Presentation Layer
• Application Layer
• Database Layer
  
  

Presentation Layer is the system with GUI where the enduser works and directly
collect the requirment from end users to be process to on the next layer(Apps Layer & DB Layer)

The Application Layer of an R/3 System is made up of the application servers and the message server. Application server is where the dispatcher distribute the work load to the different work processes(like Dailog workprocess, Background workprocess, Spool workprocess, Update Workprocess, and Enque workprocess)and makes the job done.

Database Layer is where it contains three buffer( Database buffer,SQL buffer and Redolog buffer )and as Actual database where the commited data is stored.