Lenovo System x3550 M5 Product Manual page 23

I/O expansion
The x3550 M5 server supports up to four PCIe slots: one on the system planar that is dedicated for an
internal RAID controller and up to three with different riser cards installed into two riser sockets on the
system planar (one riser socket supports the installation of one riser card). The slot form factors are listed:
Slot 1: PCIe 3.0 x16 or ML2; low profile, half-length (not present if the HDD Rear Kit is installed)
Slot 2: PCIe 3.0 x16 or PCIe 3.0 x8; low profile or full-height, half-length (PCIe 3.0 x16 slot requires
the second processor to be installed) (not present if the HDD Rear Kit is installed)
Slot 3: PCIe 3.0 x16 or PCIe 3.0 x8; low profile, half-length
Slot 4: PCIe 3.0 x8 (dedicated for an internal RAID controller)
The locations of the PCIe slots are shown in the following figure.
Figure 6. PCIe slot locations
Riser 1 supplies slot 1, and Riser 2 supplies slots 2 and 3. The slots that are available for use depend on the
number of riser cards that are installed and whether the second processor is installed:
One or two processors and no riser cards: Slot 4 is available for use
One or two processors and one riser card in riser slot 1: Slots 1 and 4 are available for use
One processor and one PCIe x16 riser card in riser slot 2: Slots 3 and 4 are available for use
One processor and one PCIe x8 riser card in riser slot 2: Slots 2, 3 and 4 are available for use
Two processors and one riser card in riser slot 2: Slots 2, 3 and 4 are available for use
Two processors and two riser cards: All slots (1, 2, 3, and 4) are available for use
Lenovo System x3550 M5 (E5-2600 v3) 23