A top view of the CPC drawer is shown in Figure 2-9. The following PU SCM feature codes relate to the resources that are enabled: Memory is connected to the SCMs through memory control units (MCUs). Up to four MCUs  are available in a drawer (one per PU SCM) to provide the interface to the controller on  memory DIMM. A memory control unit drives five DIMM slots. The CPC drawer logical diagram is shown in Figure 2-10 on page 31. This configuration supports up to two PCIe+ I/O drawers or four ICA SR adapters or one  PCIe+ I/O Drawer and two ICA SR Adapters. This configuration supports up to four PCIe+ I/O drawers or eight ICA SR adapters or a  combination not to exceed eight PCIe slots in the CPC drawer. This configuration supports one PCIe+ I/O drawer or two ICA SR adapters. Figure 2-9 CPC drawer top view and feature code comparison GLYPH<SM590000> FC 0636: One PU SCM, five DIMMs, two PCIe slots enabled GLYPH<SM590000> FC 0637: Two PU SCMs, up to 10 DIMMs, four PCIe slots enabled GLYPH<SM590000> FC 0638 and FC 0639: Four PU SCMs, up to 20 DIMMs, eight PCIe slots enabled 30  IBM 14 Model ZR1 Technical Guide