RS232 is standard on PCs. RS422, a standard in Macintosh computers, is an option commercially available for PCs. The IQ-INT II interface also supports RS422. For more information click here . It is defined by its structure and protocol.
Twisted pair is inexpensive and easy to work with, and is the best choice for most systems.
Fiber optic cable is sometimes used when there is a long distance between equipment. Although we are not aware of anyone using other technologies, there is no known reason why more exotic media such as spread spectrum could not be used. We chose the current loop method not only for cost and ease of installation, but also because a current loop is much more impervious to interference and can be used at fairly long distances without need of fiber optics or data repeaters. Factors limiting maximum distance on twisted pair include loop capacitance and total number of components connected into the loop. The limit is about 30 nF, including capacitance of the cable itself and an effective capacitance of approximately 60 pF per loop component.