2.3.3 PU characterization 2.3.4 System Controller chip In each CPC drawer, PUs can be characterized for client use. The characterized PUs can be  used in general to run supported operating systems, such as z/OS, z/VM, and Linux on  z Systems. They also can run specific workloads, such as Java, XML services, IPSec, and  some Db2 workloads, or functions, such as Coupling Facility Control Code (CFCC). For more  information about PU characterization, see 3.5, “Processor unit functions” on page 109. The maximum number of characterized PUs depends on the z14 model. Some PUs are  characterized by the system as standard system assist processors (SAPs) to run the I/O  processing. By default, least two spare PUs per system are available that are used to assume  the function of a failed PU. The remaining installed PUs can be characterized for client use. A  z14 model nomenclature includes a number that represents the maximum number of PUs  that can be characterized for client use, as listed in Table 2-2. The System Controller (SC) chip uses the CMOS 14nm SOI technology, with 17 layers of  metal. It measures 25.3 x 27.5 mm, and has 9.7 billion transistors. Each node of the CPC  drawer has one SC chip.  Figure 2-17 on page 53 shows a schematic representation of the SC chip. Consider the  following points: Table 2-2 Number of PUs per z14 model GLYPH<SM590000> X-Bus (CP-CP and CP-SC): Significant changes to allow SC to fit more X-Bus  connections GLYPH<SM590000> A Bus (SC-SC off drawer): Minor changes to reflect protocol improvements and new  system topology GLYPH<SM590000> 672 MB shared eDRAM L4 Cache GLYPH<SM590000> L4 Directory is built with eDRAM GLYPH<SM590000> New L4 Cache Management: – Ratio of L3 to L4 cache capacity is increasing – New on-drawer Cluster-to-Cluster (topology change) management 52  IBM z14 (3906) Technical Guide Model CPs IFLs Unassigned IFLs zIIP ICFs IFPs Standard  SAPs Additional  SAPs Spares M01 0 - 33 0 - 33 0 - 32 0 - 22 0 - 33 1 5 0 - 4 2 M02 0 - 69 0 - 69 0 - 68 0 - 46 0 - 69 1 10 0 - 8 2 M03 0 - 105 0 - 105 0 - 104 0 - 70 0 - 105 1 15 0 - 12 2 M04 0 - 141 0 - 141 0 - 140 0 - 94 0 - 141 1 20 0 - 16 2 M05 0 - 170 0 - 170 0 - 169 0 - 112 0 - 170 1 23 0 - 16 2