Zappiti Player 4K Duo: 2 internal HDD rack enclosures (up to 16 TB total capacity). 5x USB ports.
Zappiti Player 4K: up to 8 TB HDD via internal HDD rack enclosure. 3x USB ports.
Zappiti Player 4K Mini: only external HDDs in SATA and USB. 3x USB ports and external SATA port (instead of internal HDD rack).