USB 3.0
Universal Serial Bus 3.0, marketed as SuperSpeed USB, is the third major version of the Universal Serial Bus standard for interfacing computers and electronic devices. It was released in November 2008. The USB 3.0 specification defined a new architecture and protocol, named SuperSpeed, which included a new lane for providing full-duplex data transfers that physically required five additional wires and pins, while also adding a new signal coding scheme, and preserving the USB 2.0 architecture and protocols and therefore keeping the original four pins and wires for the USB 2.0 backward-compatibility, resulting in nine wires in total and nine or ten pins at connector interfaces. The new transfer rate, marketed as SuperSpeed USB, can transfer signals at up to , which is about 10 times faster than High-Speed. In USB 3.0 Type‑A connectors the visible inside insulators are often blue, to distinguish them from USB 2.0 connectors, as recommended by the specification, and by the initials SS.
USB 3.1, released in July 2013, is the successor specification that fully replaces the USB 3.0 specification. USB 3.1 preserves the existing SuperSpeed USB architecture and protocol with its operation mode, giving it the label USB 3.1 Gen 1. USB 3.1 introduced an Enhanced SuperSpeed System – while preserving and incorporating the SuperSpeed architecture and protocol – with an additional SuperSpeedPlus architecture adding and providing a new coding schema and protocol named SuperSpeedPlus while defining a new transfer mode called USB 3.1 Gen 2 with a signal speed of and a raw data rate of 1212 MB/s over existing Type‑A, Type‑B, and Type‑C connections, more than twice the rate of USB 3.0. Backward-compatibility is still given by the parallel USB 2.0 implementation. USB 3.1 Gen 2 Standard‑A and Standard‑B connectors are often teal-colored, though this is nonstandard.
USB 3.2, released in September 2017, fully replaces the USB 3.1 specification. The USB 3.2 specification added a second lane to the Enhanced SuperSpeed System besides other enhancements, so that SuperSpeedPlus USB implements the Gen 2×1, and the two new Gen 1×2 and Gen 2×2 operation modes while operating on two lanes. The SuperSpeed architecture and protocol still implements the one-lane Gen 1×1 operation mode. Therefore, two-lane operations, namely USB 3.2 Gen 1×2 and USB 3.2 Gen 2×2, are only possible with Full-Featured Fabrics. As of 2023, USB 3.2 Gen 1×2 and Gen 2×2 are not implemented on many products yet; Intel, however, started to include them in its LGA 1200 Rocket Lake chipsets in January 2021 and AMD in its LGA 1718 AM5 chipsets in September 2022, but Apple never provided them. On the other hand, USB 3.2 Gen 1×1 and Gen 2×1 implementations have become quite common. Again, backward-compatibility is given by the parallel USB 2.0 implementation.
Overview
The USB 3.0 specification is similar to USB 2.0, but with many improvements and an alternative implementation. Earlier USB concepts such as endpoints and the four transfer types are preserved but the protocol and electrical interface are different. The specification defines a physically separate channel to carry USB 3.0 traffic. The changes in this specification make improvements in the following areas:- Transfer speed USB 3.0 adds a new transfer type called SuperSpeed or SS, .
- Increased bandwidth USB 3.0 uses two unidirectional data paths instead of only one: one to receive data and the other to transmit.
- Power management U0 to U3 link power management states are defined.
- Improved bus use a new feature is added to let a device asynchronously notify the host of its readiness, with no need for polling.
- Support for rotating media the bulk protocol is updated with a new feature called Stream Protocol that allows a large number of logical streams within an Endpoint.
Architecture and features
In USB 3.0, dual-bus architecture is used to allow both USB 2.0 and USB 3.0 operations to take place simultaneously, thus providing backward compatibility. 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.Data transfer and synchronization
The SuperSpeed transaction is initiated by a host request, followed by a response from the device. The device either accepts the request or rejects it; if accepted, the device sends data or accepts data from the host. If the endpoint is halted, the device responds with a STALL handshake. If there is lack of buffer space or data, it responds with a Not Ready signal to tell the host that it is not able to process the request. When the device is ready, it sends an Endpoint Ready to the host which then reschedules the transaction.The use of unicast and the limited number of multicast packets, combined with asynchronous notifications, enables links that are not actively passing packets to be put into reduced power states, which allows better power management.
USB 3.0 uses a spread-spectrum clock varying by up to 5000 ppm at 33 kHz to reduce EMI. As a result, the receiver needs to continually "chase" the clock to recover the data. Clock recovery is helped by the 8b/10b encoding and other designs.
Data encoding
The "SuperSpeed" bus provides for a transfer mode at a nominal rate of, in addition to the three existing transfer modes. Accounting for the encoding overhead, the raw data throughput is, and the specification considers it reasonable to achieve or more in practice.All data is sent as a stream of eight-bit segments that are scrambled and converted into 10-bit symbols via 8b/10b encoding; this helps prevent transmissions from generating electromagnetic interference. Scrambling is implemented using a free-running linear feedback shift register. The LFSR is reset whenever a COM symbol is sent or received.
Unlike previous standards, the USB 3.0 standard does not specify a maximum cable length, requiring only that all cables meet an electrical specification: for copper cabling with AWG 26 wires, the maximum practical length is.
Power and charging
As with earlier versions of USB, USB 3.0 provides power at 5 volts nominal. The available current for low-power SuperSpeed devices is 150 mA, an increase from the 100 mA defined in USB 2.0. For high-power SuperSpeed devices, the limit is six unit loads or 900 mA —almost twice USB 2.0's 500 mA.USB 3.0 ports may implement other USB specifications for increased power, including the USB Battery Charging Specification for up to 1.5 A or 7.5 W, or, in the case of USB 3.1, the USB Power Delivery Specification for charging the host device up to 100 W.
Naming scheme
Starting with the USB 3.2 specification, USB-IF introduced a new naming scheme. To help companies with branding of the different operation modes, USB-IF recommended branding the 5, 10, and capabilities as SuperSpeed USB 5Gbps, SuperSpeed USB 10 Gbps, and SuperSpeed USB 20 Gbps, respectively.In 2023, they were replaced again, replacing "SuperSpeed" with USB 5Gbps, USB 10Gbps, and USB 20Gbps, and introducing new Packaging and Port logos.
Availability
The USB 3.0 Promoter Group announced on 17 November 2008 that the specification of version 3.0 had been completed and had made the transition to the USB Implementers Forum, the managing body of USB specifications. This move effectively opened the specification to hardware developers for implementation in future products.The first USB 3.0 consumer products were announced and shipped by Buffalo Technology in November 2009, while the first certified USB 3.0 consumer products were announced on 5 January 2010, at the Las Vegas Consumer Electronics Show, including two motherboards by Asus and Gigabyte Technology.
Manufacturers of USB 3.0 host controllers include, but are not limited to, Renesas Electronics, Fresco Logic, ASMedia, Etron, VIA Technologies, Texas Instruments, NEC and Nvidia. As of November 2010, Renesas and Fresco Logic have passed USB-IF certification. Motherboards for Intel's Sandy Bridge processors have been seen with Asmedia and Etron host controllers as well. On 28 October 2010, Hewlett-Packard released the HP Envy 17 3D featuring a Renesas USB 3.0 host controller several months before some of their competitors. AMD worked with Renesas to add its USB 3.0 implementation into its chipsets for its 2011 platforms. At CES2011, Toshiba unveiled a laptop called "Qosmio X500" that included USB 3.0 and Bluetooth 3.0, and Sony released a new series of Sony VAIO laptops that would include USB 3.0. As of April 2011, the Inspiron and Dell XPS series were available with USB 3.0 ports, and, as of May 2012, the Dell Latitude laptop series were as well; yet the USB root hosts failed to work at SuperSpeed under Windows 8.
Adding to existing equipment
On the motherboards of desktop PCs which have PCI Express slots, USB 3.0 support can be added as a PCI Express expansion card. 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 of power that each USB 3.0 port is capable of, whereas the PCI Express slot itself cannot supply the required amount of power.If faster connections to storage devices are the reason to consider USB 3.0, an alternative is to use eSATAp, possibly by adding an inexpensive expansion slot bracket that provides an eSATAp port; some external hard disk drives provide both USB and eSATAp interfaces. To ensure compatibility between motherboards and peripherals, all USB-certified devices must be approved by the USB Implementers Forum. At least one complete end-to-end test system for USB 3.0 designers is available on the market.