In general terms, a host adapter (also sometimes called a host bus adapter) is a device which connects a computer (the host system) to other peripheral devices. Within the computer, there are many ICs on the motherboard communicating using various protocols, such as PCIe, SATA, SMBus, USB, etc. But within the world of electronics, interesting sensors, actuators, and application-specific ICs use several different standard protocols such as SPI, I2C, 1-WIRE, and SWI. These protocols are not typically supported directly by the motherboard chipset or otherwise exposed, either physically or programmatically, for user access.