Types of work processes:
Message : Coordinates the communication between different instances of a single SAP R/3 system. Used for Logon purpose and load balancing.
Dispatcher : Redirect the request from GUI client to free process.
Dialog : Interpreting the ABAP code and execute the business logic. Used for interactive online processing.
Batch : For Background jobs.
Enqueue : Single “Central Lock Management Service” that controls the locking mechanism between the different application servers and the database.
Update : Responsible for consistency in asynchronous data changes.
Gateway : Used for transport of bigger amount of data between application servers as well as external (non SAP) systems that communicate with SAP.