Architecture (SAP NetWeaver PI Dual-Stack) 
The following figure shows the main components of an SAP NetWeaver PI dual-stack installation.
The main components for design and configuration time are the Enterprise Services Repository (ES Repository) and the Integration Directory. Using these tools, an integration expert designs integration content (for example, interfaces and process integration scenarios) and specifies the configuration settings for message exchange for a specific system landscape. The design and configuration tools are connected to the System Landscape Directory which contains, for example, the description of software components and systems. The ES Repository and the Integration Directory are technically based on AS Java.
The Integration Directory is connected to the ES Repository to allow access to specific design time objects (for example, mappings) also at configuration time.
More information:
When you install SAP NetWeaver PI (dual-stack installation option), you set up an “Integration Server”. The Integration Server hosts the following runtime engines:
Integration Engine (based on AS ABAP)
Business Process Engine (based on AS ABAP)
More information: Cross-Component Business Process Management
Advanced Adapter Engine (based on AS Java)
Note
All SAP systems based on Application Server ABAP release 6.20 or higher contain a “local” Integration Engine, also when used as an application system. This local Integration Engine enables the system — when used as an application system — to connect to another system via an SAP NetWeaver PI runtime engine. This kind of connectivity is also referred to as connectivity based on the proxy runtime. All other systems – either SAP or third-party – connect to the SAP NetWeaver PI runtime using adapters.
More information: Connectivity
To process messages, the involved runtime engines use information from the Integration Directory. This information is made available to the runtime engines using runtime caches.
More information: Runtime Caches