Important categories of Profile Parameters in SAP

These are important categories of system parameters. You can access and change them using RZ11.
to
display you can use report RSPFPAR which can be run thorough SA38. Not
all parameters can be changed.Using RZ10 (profile maintainance) 
you can change parameters that are dynamically switchable and they are
activated immediately.

• ES/* : Related to extended memory settings
• INSTANCE* : Identify an instance or server
• ABAP/* : Related to program execution, including heap settings
• AUTH/* : Related to authorization
• DBS/<DB Type/* : Database specific parameters
• EM/* : General system related settings
• ENQUE/* : Settings for the enqueue WP (or standalone ENQ server)
• GW/* : SAP Gateway related settings
• ICF/* & ICM/* : Settings for the Internet control framework and ICM
• LOGIN/* : Controls the logon environment (such a multiple sessions etc)
• MS/* : Message server related settings
• RDISP/* : Controls the dispatcher & dispatcher controlled processes
• STAT/* : Statistics collector related parameters
• SCSA/* : Shared common system area parameters
• ZTTA/* : Extended memory related parameters