Chosen Solution

Is it possible to add a second drive (HDD or SSD) to an SSD equipped (only) system? Would any parts be necessary or does the iMac already include them inside?

From what I’ve seen in the Apple Store this model supports a Fusion Drive so it has to suport 2 drives, blade ssd and sata drive. If is a ssd only model the SATA cable would be missing but the motherboard should have still the sata connector