Among other improvements, USB 3.0 adds the new transfer rate referred to as SuperSpeed USB (SS) that can transfer data at up to 5 Gbit/s (625 MB/s), which is about 10 times faster than the USB 2.0 standard. The USB 3.0 specification is similar to USB 2.0, but with many improvements and an alternative implementation. The USB 3.0 specification is the combination of the physical SuperSpeed bus combined in parallel with the physical USB 2.0 bus. Similar principle of backward compatibility applies to connecting a USB 2.0 Standard-A plug into a USB 3.0 Standard-A receptacle. The maximum cable length is not specified in the document, length is defined as still meeting the other electrical requirements. The table below helps give an overview of the various types and formats. USB standards There is a good variety of different USB connectors to enable connectivity in a variety of situations. The pinouts for the 10 pin micro-B USB 3.0 plug connector are: Micro-USB 3.0 cable pinout; Micro-USB 3.0 connector pinout The available current for low-power (one unit load) SuperSpeed devices is 150 mA, an increase from the 100 mA defined in USB 2.0. The basic USB pinouts for the connectors are given in the table below. On 11 June 2012, Apple announced new MacBook Airs and MacBook Pro with USB 3.0. The USB 3.0 specification is the combination of the physical SuperSpeed bus combined in parallel with the physical USB 2.0 bus.
The structural topology is the same, consisting of a tiered star topology with a root hub at level 0 and hubs at lower levels to provide bus connectivity to devices. The device either accepts the request or rejects it; if accepted, the device sends data or accepts data from the host. The Standard-B is used at the device side. In addition to an empty PCIe slot on the motherboard, many "PCI Express to USB 3.0" expansion cards must be connected to a power supply such as a Molex adapter or external power supply, in order to power many USB 3.0 devices such as mobile phones, or external hard drives that have no power source other than USB; as of 2011, this is often used to supply two to four USB 3.0 ports with the full 0.9 A (4.5 W) of power that each USB 3.0 port is capable of (while also transmitting data), whereas the PCI Express slot itself cannot supply the required amount of power. Each shielded pair includes its own drain wire, one for each pair; however both drain wires are attached to a single pin on the connector. Apart from the connectors that are standardised, the cable lengths are also defined: the maximum allowable length for an individual cable is 5 metres (3 metres for slow devices) and this allows the USB data acquisition module to be located remotely from the computer. The wire is color coded per the drawing above, the Drain Wire is by definition uninsulated.