Architecture of the SAP NetWeaver Application Server 
SAP NetWeaver Application Server can be installed in various specifications depending on the SAP product and applications used. A distinction is made between ABAP systems, Java systems, and dual-stack systems.
Depending on the SAP product used, not every specification may be available.
Specifications of SAP NetWeaver Application Server
A pure ABAP system provides the complete infrastructure for developing and running ABAP-based applications. With an installed ABAP system, both ABAP applications and selected SAP Java applications can be run.
A pure Java system provides a Java™ 2 Enterprise Edition (Java EE) 1.6 compliant-environment for developing and running Java EE programs. With a Java installation you can run Java EE applications, but not any ABAP applications.
A dual stack system provides the complete infrastructure for developing and running both ABAP-based applications and Java EE-based applications.
Since the architecture of SAP NetWeaver Application Server depends on the specifications installed, below is a list of references to system-specific architecture documentation.