What are the different type of work process ?

A. The following work process in SAP R/3

• Dialog (D): each dispatcher needs at least 2 dialog work processes (not shown
  above)
• Spool (S): at least 1 per R/3 System (more than 1 per dispatcher allowed)
• Update (V): at least 1 per R/3 System (more than 1 per dispatcher allowed)
• Background (B): at least 2 per R/3 System (more than 1 per dispatcher allowed)
• Enqueue (E): exactly 1 per R/3 System (only 1 E work process is required and
  allowed)