The first thing to note about USB 3.0 (also referred to as USB 3.1 Gen 1 since 2015) is that although it is a new specification, first released in 2008, it is really an enhancement to existing specifications. Therefore, a USB 3.0 device is backward compatible with USB 2.0 devices. This allows USB 3.0 devices to function with USB 2.0 or USB 3.0 hosts. There are two important features in the new specification: the top speed for data transfer is now 4.8Gbps – a 10x improvement over USB 2.0, and the maximum power that a USB 3.0 host port can deliver is 900 mA. To facilitate the extra speed, new connectors have also been defined, specific to USB 3.0, which provide full duplex differential USB signaling for USB TX+/- and USB RX+/- in addition to the original half duplex USB 2.0 USB DP/DM.