What Are SAP PAS, AAS, and ASCS?

PAS stands for the primary application server.

AAS stands for the additional application server.

ABAP Central Services (ASCS) is the core SAP application service. It consists of following servers:

• Message Server: works as a load balancer. All user requests are first processed by the message server and then distributed to each SAP application server.
• Enqueue Server: manages lock table. To prevent different operations from modifying a record at the same time, the table is locked to ensure data consistency.

The differences between the PAS and a AAS: The PAS contains the ASCS, but an AAS does not. In a system, there is only one PAS, but there can be multiple AASs. The number depends on the service requirements.

If any problem occurs in the ASCS, the entire SAP system breaks down. Therefore, adopt the HA architecture for the ASCS.