A configuration that includes PCIe+ I/O drawers 3 and 4 is shown in Figure G-7. This  configuration requires four PU SCMs to be installed. Rear view 4 PU SCMs (FC 0638 or 0639) 4 PU SCMs (FC 0638 or 0639) Figure G-7 PDU cabling with three or four PCIe+ I/O drawers installed Appendix G. 16U Reserved feature  471