The PCIe riser that installs in PCIe slots 3 and 4 is different than the risers in PCIe slots 1 and 2. The riser for slots 3 and 4 supports two cards, a standard PCIe card and an internal HBA card. Do not attempt to install the riser for PCIe slots 3 and 4 in slots 1 or 2, and vice versa.
Figure 56 PCIe Riser Locations
1 PCIe riser and installed PCIe card in slot 1 (This slot is nonfunctional in single-processor systems.)
2 PCIe riser and installed PCIe card in slot 2
3 PCIe riser and installed cards (2) in slots 3 and 4 (this riser contains the internal HBA card.) Note: This riser is different from the risers in slots 1 and 2.