Apple Desktop Bus (ADB) is a bit-serial peripheral bus connecting low-speed devices to computers. It was introduced on the Apple IIGS in 1986 as a way to support low-cost devices like keyboards and mice, allowing them to be connected together in a daisy chain without the need for hubs or other devices. ADB was quickly introduced on later Macintosh models, on later models of NeXT computers, and saw some other 3rd party use as well. Like the similar PS/2 connector used in many PC-compatibles at the time, ADB was rapidly replaced by USB as that system became popular in the late 1990s; the last external ADB port on an Apple product was in 1999, though it remained as an internal-only bus on some Mac models into the 2000s.