Attention: z/OS® supports two space-related parameters called MXIG and ALX. Use these parameters with extreme caution for VIO as well as non-VIO allocations. You can specify them as subparameters of the JCL SPACE keyword. You can also specify them to the system as defaults in the allocation parmlib member ALLOCxx, in which case they get applied for VIO and dynamic allocation requests if space parameters are not specified. In these cases instead of allocating the requested space quantity the allocated space is based on MXIG or ALX values. See z/OS DFSMS Using Data Sets for details on the actual amount of space allocated. For VIO allocations, this can result in affecting paging space and continued operation of the system if all of the allocated space is actually used. These parameters can be overridden by the dynamic allocation installation exit. The value passed to the SMS ACS routines for the read-only variables &SIZE and &MAXSIZE are based on the user-specified space quantity and are not based on MXIG or ALX.