An MES upgrade requires IBM SSRs for the installation. In most cases, the time that is  required for installing the LICCC and completing the upgrade is short. To better use the MES upgrade function, carefully plan the initial configuration to allow a  concurrent upgrade to a target configuration. The availability of PCIe+ I/O drawers improves  the flexibility to perform unplanned I/O configuration changes concurrently. The Store System Information (STSI) instruction gives more useful and detailed information  about the base configuration and temporary upgrades. The model and model capacity identifiers that are returned by the STSI instruction are  updated to coincide with the upgrade. For more information, see “Store System Information  instruction” on page 376. Upgrades:  An MES provides the physical upgrade, which results in more enabled  processors, different capacity settings for the CPs, and more memory, I/O ports, I/O  adapters, and I/O drawers. Extra planning tasks are required for nondisruptive logical  upgrades. For more information, see “Guidelines to avoid disruptive upgrades” on  page 378. An MES upgrade for processors can concurrently add CPs, ICFs, zIIPs, IFLs, and SAPs to a  z15 server by assigning available PUs on the processor drawers through LICCC. Depending  on the quantity of the extra processors in the upgrade, more processor drawers might be  required, and can be concurrently installed before the LICCC is enabled if plan-ahead  features are available. With the subcapacity models, more capacity can be provided by  adding CPs, changing the capacity identifier on the current CPs, or both. Limits:  The sum of CPs, inactive CPs, ICFs, zIIPs, IFLs, unassigned IFLs, and SAPs  cannot exceed the maximum limit of PUs available for client use. The number of zIIPs  cannot exceed twice the number of purchased CPs.  8.3.1 MES upgrade for processors 346  IBM z15 (8561) Technical Guide