In addition to the IEASYSxx GRS= parameter indicating how GRS should initialize the system, the PLEXCFG= parameter allows the installation to indicate the processing environment into which the system is being IPLed. The GRS= system parameter is checked against this parameter to ensure that the system is being initialized properly for the particular environment the installation wants to establish. The relationship of the GRS=STAR parameter to the options that can be specified on the PLEXCFG= parameter is described in Table 1. The PLEXCFG=options and their meanings can be found in z/OS MVS Initialization and Tuning Reference.