There are three external and one internal PCIe slots available in the Oracle ZFS Storage ZS5-ES. The external slots support optional, standard PCIe cards and are numbered 1, 2, and 3 from left to right when you view the controller from the rear. The internal slot, which installs on the riser in PCIe slots 3 and 4, supports a required internal SAS controller HBA card. For a view of the rear panel that shows PCIe slot numbering, see Controller Back Panel View.