IBM 8001-22C Manual page 100

Figure 52. Sliding the tail-stock retainer to the closed position
Go to step 6 on page 87.
5. To install an adapter in position 5, 6, 7, and 8, remove the riser as shown in Figure 53.
Figure 53. Removing the PCIe riser
a. Retract the retaining pin (A) so the arrow is pointing to the system.
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Power Systems: Installing the IBM Power System S822LC for Big Data (8001-22C)