Higher data rates are enabled by a transmission technology similar to PCI-Express or Serial ATA, which requires two additional pairs of wires in the cable, in addition to the existing data pair (D+/D-), plus an additional ground connection. As a result, five additional contacts are required in the connectors, leading to the introduction of new connectors and cables with USB 3.0. These new Type A connectors are backward compatible with the previous ones. Existing USB devices can still be used with USB 3.0, and new 3.0 devices can also operate on older 2.0 or 1.0/1.1 hosts. An exception is made for B-, Mini-B-, Micro-B-, and Mini-A connectors. While older plugs can fit into new sockets, new plugs cannot be used in old sockets without the need for adapters.