Part of the application layer of an AS ABAP. The application layer can be distributed to several application servers, these are usually instantiated on different computers whose operating systems do not need to be identical. However, several application servers of one or more AS ABAP may run on one computer. Application servers communicate with the presentation layer, the database layer, and with each other via the message server. The most important components of an application server are its work processes, the number and type of which are determined when the ABAP-based SAP System is started. An ABAP program is executed by a suitable application server work process. The storage areas of an application server, which can be accessed in the ABAP programs, are the shared memory, the SAP memory, the ABAP memory and the roll area in the internal session.