The TSOLIB command, introduced with TSO/E Release 5, allows users to dynamically link to load module libraries of their choice while remaining in their active TSO/E session. The TSOLIB command saves your installation from having to maintain several versions of logon procedures, or several user IDs with different logon procedures, for programmers who require the allocation of different versions of load module libraries.

Using the TSOLIB command to link to libraries or products — only when required — allows your installation to reduce the number of different logon procedures and to simplify existing logon procedures. You can reduce the number of default data set allocations at logon time, thus gaining improved performance.

See for command details and advantages of the TSOLIB command. Also, see Customizing the TSOLIB command for details about writing exits.