A host adapter, host bus adapter (HBA), or host controller is a part of a computer that allows communication with devices such as hard drives, Ethernet, fibre, FireWire, IDE, SCSI, or USB. It allows the main computer processor to communicate and process information between itself and the device or the network. The picture shows a VIA VT6308S chip on a computer motherboard and is an example of a Host Controller for IEEE 1394 (FireWire).
While some host adapter can be added to a computer, like a PCI card, others are integrated into the computer motherboard, like those used for connecting a hard drive to a computer. Integrated host adapter are commonly referred to as IDE ports or SATA ports on a motherboard.