Sonnet Echo Express SEII Thunderbolt 2-to-PCIe Expansion Chassis (Echo-EXP-SE2) Use high-performance PCIe card with Thunderbolt-equipped computers Maximum performance with computers with 20Gbps Thunderbolt 2 technology, backward compatible with 10Gbps Thunderbolt technology When available, upgrade to 40Gbps Thunderbolt 3 Technology with a replacement Thunderbolt interface card Support two half-length+ (up to 7.75" long), full-height, single-width cards (plus one daughter card) Automatically operates slowly and quietly with cooler cards, provides better cooling for hot cards