The high-gloss black Thunderstor XR4 Rackmount PCIe Expansion Chassis from Rocstor can be used for connecting HBA, RAID, or video cards to a Mac via Thunderbolt connection. The Thunderstor XR4 Rackmount expansion chassis supports all compatible PCIe cards, up to full-height and full-length peripherals. It provides extra DC power connections for GPUs requiring those connections. The Thunderstor XR4 offers four full-bandwidth PCIe slots, using two independent Thunderbolt 20 Gb/s bridge circuits. One Thunderbolt Bridge drives two slots, and a second internal Thunderbolt bridge drives the other two slots. Connections to the host Mac Pro include using two of the three available Thunderbolt bus connections to the Mac. Daisy-chain expansion beyond the Thunderstor XR4 is also available via its four Thunderbolt expansion ports.