4.3 PCIe+ I/O drawer The PCIe+ I/O drawers (see Figure 4-1) are attached to the CPC drawer through a PCIe  cable and use PCIe as the infrastructure bus within the drawer. The PCIe I/O bus  infrastructure data rate is up to 16 GBps. PSU PSU PCIe Switch PCIe Switch FSP FSP Figure 4-1 Rear view of PCIe+ I/O drawer PCIe switch application-specific integrated circuits (ASICs) are used to fan out the host bus  from the CPC drawer through the PCIe+ I/O drawer to the individual I/O features. Maximum  16 PCIe I/O features (up to 32 channels) per PCIe+ I/O drawer are supported.  The PCIe+ I/O drawer is a one-sided drawer (all I/O cards on one side, in the rear of the  drawer) that is 8U high. The PCIe+ I/O drawer contains the 16 I/O slots for PCIe features, two  switch cards, and two power supply units (PSUs) to provide redundant power, as shown in  Figure 4-1.  122  IBM 14 Model ZR1 Technical Guide