The spinning disc drive is SATA and non proprietary (https://www.ifixit.com/Guide/iMac+Intel+27-Inch+EMC+2546+Bla...). The SSD is not and use a proprietary PCI-e connector (https://www.ifixit.com/Guide/iMac+Intel+27-Inch+EMC+2546+Bla...). You can find adapters though (https://www.amazon.de/Sintech-M-2-PCIe-2280-SSD-Karte-MZ-JPU...).