RS-422 specifies differential signaling, with every data line paired with a dedicated return line. It is the voltage difference between these two lines that define the mark and space, rather than, as in RS-232, the difference in voltage between a data line and a local ground. As the ground voltage can differ at either end of the cable, this required RS-232 to use signals with voltage magnitudes greater than 5 volts. Moving to dedicated return lines and always defining ground in reference to the sender allowed RS-422 to use 0.4 V, allowing it to run at much higher speeds. RS-423 differed primarily in that it had a single return pin instead of one for each data pin.