USB, or Universal Serial Bus, is the most popular choice for connecting external audio devices to computers. In the pro-audio market many devices also use IEEE1394 or FireWire, but it is rapidly disappearing from most popular personal computers, especially Windows-based PCs. Higher-end Apple products still have it, but Windows 8 may not have any support for it at all.  USB is the best choice for audiophile computer audio devices such as a USB to SPDIF transport/converter.