USB 3.X Specification
Wikipedia link USB 3.0
Informations
The USB 3.0 specification was released on 12 November 2008, with its management transferring from USB 3.0 Promoter Group to the USB Implementers Forum (USB-IF), and announced on 17 November 2008 at the SuperSpeed USB Developers Conference.
USB 3.0 adds a SuperSpeed transfer mode, with associated backward compatible plugs, receptacles, and cables. SuperSpeed plugs and receptacles are identified with a distinct logo and blue inserts in standard format receptacles.
The SuperSpeed bus provides for a transfer mode at a nominal rate of 5.0 Gbit/s, in addition to the three existing transfer modes. Its efficiency is dependent on a number of factors including physical symbol encoding and link level overhead. At a 5 Gbit/s signaling rate with 8b/10b encoding, each byte needs 10 bits to transmit, so the raw throughput is 500 MB/s. When flow control, packet framing and protocol overhead are considered, it is realistic for 400 MB/s (3.2 Gbit/s) or more to transmit to an application. Communication is full-duplex in SuperSpeed transfer mode; earlier modes are half-duplex, arbitrated by the host.
Low-power and high-power devices remain operational with this standard, but devices using SuperSpeed can take advantage of increased available current of between 150 mA and 900 mA, respectively.
USB 3.1, released in July 2013 has two variants. The first one preserves USB 3.0’s SuperSpeed transfer mode and is labeled USB 3.1 Gen 1, and the second version introduces a new SuperSpeed+ transfer mode under the label of USB 3.1 Gen 2. SuperSpeed+ doubles the maximum data signaling rate to 10 Gbit/s, while reducing line encoding overhead to just 3% by changing the encoding scheme to 128b/132b.
USB 3.2, released in September 2017, preserves existing USB 3.1 SuperSpeed and SuperSpeed+ data modes but introduces two new SuperSpeed+ transfer modes over the USB-C connector with data rates of 10 and 20 Gbit/s (1.25 and 2.5 GB/s). The increase in bandwidth is a result of multi-lane operation over existing wires that were intended for flip-flop capabilities of the USB-C connector.
USB 3.0 also introduced the UASP protocol, which provides generally faster transfer speeds than the BOT (Bulk-Only-Transfer) protocol.
USB 3.1
In January 2013 the USB group announced plans to update USB 3.0 to 10 Gbit/s (1250 MB/s). The group ended up creating a new USB specification, USB 3.1, which was released on 31 July 2013, replacing the USB 3.0 standard. The USB 3.1 specification takes over the existing USB 3.0’s SuperSpeed USB transfer rate, also referred to as USB 3.1 Gen 1, and introduces a faster transfer rate called SuperSpeed USB 10 Gbps, referred to as USB 3.1 Gen 2, putting it on par with a single first-generation Thunderbolt channel. The new mode’s logo features a caption stylized as SUPERSPEED+. The USB 3.1 Gen 2 standard also reduces line encoding overhead to just 3% by changing the encoding scheme to 128b/132b, with effective data rate of 1,212 MB/s. The first USB 3.1 Gen 2 implementation demonstrated real-world transfer speeds of 7.2 Gbit/s.
The USB 3.1 standard is backward compatible with USB 3.0 and USB 2.0. It defines the following transfer modes:
USB 3.1 Gen 1
SuperSpeed, 5 Gbit/s data signaling rate over 1 lane using 8b/10b encoding (effective 500 MB/s); the same as USB 3.0. This rebranding of USB 3.0 as “USB 3.1 Gen 1” has allowed manufacturers to advertise products with transfer rates of only 5 Gbit/s as “USB 3.1,” omitting the generation. The nominal data rate in bytes accounts for bit-encoding overhead. The physical SuperSpeed bit rate is 5 Gbit/s. Since transmission of every byte takes 10 bit times, the raw data overhead is 20%, so the byte rate is 500 MB/s, not 625.
USB 3.1 Gen 2
SuperSpeed+, new 10 Gbit/s data rate over 1 lane using 128b/132b encoding (effective 1212 MB/s)
Similarly, at SS+ rate the encoding is 128b/132b, so transmission of 16 bytes physically takes 16.5 bytes, or 3% overhead. Therefore, the byte-rate at SS+ is 128/132 * 10 Gbit/s = 9.697 GBit/s = 1212 MB/s. In reality the SS bus has some additional service overhead (link management, protocol response, host latencies), so the best-case achievable data rates are about 10% smaller.
USB 3.2
On 25 July 2017, a press release from the USB 3.0 Promoter Group detailed a pending update to the USB Type-C specification, defining the doubling of bandwidth for existing USB-C cables. Under the USB 3.2 specification, released 22 September 2017, existing SuperSpeed certified USB-C 3.1 Gen 1 cables will be able to operate at 10 Gbit/s (up from 5 Gbit/s), and SuperSpeed+ certified USB-C 3.1 Gen 2 cables will be able to operate at 20 Gbit/s (up from 10 Gbit/s). The increase in bandwidth is a result of multi-lane operation over existing wires that were intended for flip-flop capabilities of the USB-C connector.
The USB 3.2 standard is backward compatible with USB 3.1/3.0 and USB 2.0. It defines the following transfer modes:
USB 3.2 Gen 1 – SuperSpeed, 5 gigabits per second (Gbit/s) data signaling rate over 1 lane using 8b/10b encoding (effective 500 MB/s) , the same as USB 3.1 Gen 1 and USB 3.0. USB 3.2 Gen 2 – SuperSpeed+, 10 gigabits per second (Gbit/s) data rate over 1 lane using 128b/132b encoding (effective 1,212 MB/s), the same as USB 3.1 Gen 2. USB 3.2 Gen 1×2 – SuperSpeed+, new 10 gigabits per second (Gbit/s) data rate over 2 lanes using 8b/10b encoding (effective 1 GB/s). USB 3.2 Gen 2×2 – SuperSpeed+, new 20 gigabits per second (Gbit/s) data rate over 2 lanes using 128b/132b encoding (effective 2,424 MB/s). As with the previous version, the same considerations around encoding and effective data rates apply. Although both Gen 1 and 2 signal at 10 Gbit/s, Gen 1 uses the older, less efficient line coding which results in smaller byte-rate.
In May 2018, Synopsys demonstrated the first USB 3.2 Gen 2×2 connection, where a Windows PC was connected to a storage device, reaching an average speed of 1600 MB/s.
USB 3.2 is supported with the default Windows 10 USB drivers and in Linux kernels 4.18 and onwards.
In February 2019, USB-IF simplified the marketing guidelines and required the SuperSpeed trident logos to include maximum transfer speed.
Summary
| USB-IF recommended marketing name | Logo | Transfer mode | Older specifications | Dual-lane | Encoding | Nominal speed | Effective speed | Connectors |
|---|---|---|---|---|---|---|---|---|
| SuperSpeed USB 5Gbps |  |
USB 3.2 Gen 1×1 | USB 3.1 Gen 1, USB 3.0 | No | 8b/10b | 5 Gbit/s | 0.5 GB/s | USB-A, B, micro B & USB-C |
| SuperSpeed USB 10Gbps |  |
USB 3.2 Gen 2×1 | USB 3.1 Gen 2, USB 3.1 | No | 128b/132b | 10 Gbit/s | 1.2 GB/s | USB-A, B, micro B & USB-C |
| - | - | USB 3.2 Gen 2×2 | – | Yes | 8b/10b | 10 Gbit/s | 1 GB/s | USB-C |
| SuperSpeed USB 20Gbps |  |
USB 3.2 Gen 2×2 | - | Yes | 128b/132b | 20 Gbit/s | 2.4 GB/s | USB-C |
- First Release date: Novembre 2008.
- Maximum transfer rate : 5, 10 or 20 Gbit/s
- Maximum theoretical data throughput: 0.6, 1.2 or 2.4 GByte/s
- Names: SuperSpeed
- Connectors: Standard Type A SuperSpeed, Standard Type B SuperSpeed, , Micro A SuperSpeed, Micro B SuperSpeed, Micro AB SuperSpeed, Type C
- Current: 0.15A to 5A
- Voltage: 5V ± 5% 4.40–5.25 V
- Power: 0.75W to 240W
- Signal: 5V DC or 20V DC
- Cable Length: Electrical specification depending( Copper cabling with AWG26 wires, limit is 3m) 9ft 10in
Connectors
Charging capabilities compatible with USB 3.X
| Specification | Current | Voltage | Power (max.) | Emarker |
|---|---|---|---|---|
| USB 3.0 Low-power device | 0.15A | 5V | 0.75W | No |
| USB 3.0 High-power device | 0.9A | 5V | 4.5W | No |
| USB 3.0 Multi-lane (USB 3.2 Gen x2) device | 1.5A | 5V | 7.5W | No |
| USB-C | 1.5A | 5V | 7.5W | No |
| USB-C | 3A | 5V | 15W | No |
| Power Delivery 1.0 Micro-USB | 3A | 20V | 60W | No |
| Power Delivery 1.0 Type-A/B | 5A | 20V | 100W | Yes |
| Power Delivery 2.0/3.0 Type-C | 5A | 20V | 100W | Yes |
| Power Delivery 3.1 Type-C | 5A | 48V | 240W | Yes |
| Battery Charging (BC) 1.1 | 1.5A | 5V | 7.5W | No |
| Battery Charging (BC) 1.2 | 5A | 5V | 25W | No |