Chosen Solution
When buying the 1TB SSD with the iMac directly from Apple: Is it a PCI-Express SSD then? Is the main HDD-Slot empty in this case (hence could I add another HDD later on?) Doing the upgrade via Apple is like 400$ more expensive than upgrading yourself. Is the PCI Express SSD worth it? (If this is what apple uses)
Your system has two drive ports: a custom PCIe x4 for a blade SSD and a SATA III (6.0 Gb’s) for a traditional 3.5" HD. If you review the IFIXIT teardown here: iMac Intel 27" Retina 5K Display Teardown you can see whats what.
