IEASYSxx holds system parameters and is described in the MVS™ Initialization and Tuning Reference (SA22-7592). The following directives are known to impact z/OS® Explorer:

This parameter specifies a value that, under most conditions, the system uses to limit the number of jobs and started tasks that can run concurrently during a given IPL.

Value Range: nnnnn is a decimal value from 0-32767. Note that the
           sum of the values specified for the MAXUSER, RSVSTRT,
           and RSVNONR system parameters cannot exceed 32767.
Default Value: 255