To support Redundant I/O Interconnect (RII) between domain pair 0 and 1, the two  interconnects to each pair must be driven from two different PCIe fanouts. Normally, each  PCIe interconnect in a pair supports the eight features in its domain. In backup operation  mode, one PCIe interconnect supports all 16 features in the domain pair. Note:  The PCIe Gen3 Interconnect (switch) adapter must be installed in the PCIe+ I/O  drawer to maintain the interconnect across I/O domains. If the adapter is removed (for a  service operation), the I/O cards in that domain (up to eight) become unavailable. All fanouts that are used for I/O and coupling links are rebalanced if the upgrade does not  involve adding components inside the CPC drawer. If MES involves extra components, such  as PU SCMs and Memory DIMMs, the change is disruptive.  When a z14 ZR1 is ordered, the PUs are characterized according to their intended usage.  The PUs can be ordered as any of the following items:  A minimum of one PU that is characterized as a CP, IFL, or ICF is required per system. The  maximum number of characterizable PUs is 30 (any combination of 6 CPs, 30 IFLs, 30 ICF,  two more SAP$^{10}$s, and 12 ZIIPs). The maximum number of zIIPs is up to twice the number of  PU that are characterized as CP.  Remainder:  Not all PUs on a model must be characterized. 2.7.2 CPC drawer upgrades CP The processor is purchased and activated. PU supports the z/OS,  z/VSE, z/VM, z/TPF, and Linux on Z$^{9}$ operating systems. It can also  run Coupling Facility Control Code. Capacity marked CP A processor that is purchased for future use as a CP is marked as  available capacity. It is offline and not available for use until an upgrade  for the PU is installed. It does not affect software licenses or  maintenance charges. IFL The Integrated Facility for Linux (IFL) is a processor that is purchased  and activated for use by z/VM for Linux guests and Linux on Z$^{9}$  operating systems. Unassigned IFL  A processor that is purchased for future use as an IFL. It is offline and  cannot be used until an upgrade for the IFL is installed. It does not  affect software licenses or maintenance charges. ICF  An internal coupling facility (ICF) processor that is purchased and  activated for use by the Coupling Facility Control Code. zIIP  An “Off Load Processor” for workload that is restricted to Db2 type  applications. Additional SAP  An optional processor that is purchased and activated for use as an  SAP (System Assist Processor).  9 The KVM hypervisor is part of select Linux on Z distributions. 10 Two standard SAPs with every ZR1 system are always featured. Up to two more SAPs can be ordered. The extra  SAPs are part of the customer characterizable PUs. Chapter 2. Central processor complex hardware components  51