The SAP ABAP 3-tier architecture has 3 major layers. They are:

• Presentation Layer: It is an interface or program known as “sapgui.exe” installed on a PC or Workstation of a user. This interface will accept user inputs in the form of mouse clicks, function keys, or keystrokes and will send the request that NEEDS to be processed by the application server. The application server will send the result back to the interface and output formatting will be done in order to display it to the user.
• Application Layer: This is an executable set that togetherly does ABAP/4 program interpretation and will also be able to do input/output MANAGEMENT for them. When the application server gets started each and every executable will get started at the same time and when the application server stops, they shut down together. The details about the number of the process that began during the starting of the application server will be specified in a single configuration file known as Application Server PROFILE. The application server is in existence for interpreting and running the ABAP/4 programs. It is possible for an ABAP/4 program to start an executable on the presentation server but the execution of them is not possible. When an ABAP/4 program makes a request for the data from the database, then that request will be formatted by the application server, and finally, the formatted request will be sent to the database server.
• Database Layer: This is an executable set that will accept requests for the database that came from the application server. The requests will be passed on to the database, it will be processed and information will be sent back to the database server, from there it will be later passed on to the application server. The application server will pass on this database RETRIEVED information to the ABAP/4 program.