Host Channel Adapter, the IB component that connects a processor to other IB devices. An HCA is really a bridge and must communicate with both other HCAs and TCAs. HCAs hook up, somehow, to your PC. Just how isn’t yet established, though I expect they’ll be integrated onto the motherboard, presenting an external physical connector for linking. It should allow I/O subsystems, like Ethernet, Fibre Channel, SCSI and interprocessor communication, to converse through the InfiniBand switch fabric, without complex hardware or software interfaces.