In January 2013 the USB group announced plans to update USB 3.0 to 10 Gbit/s (1.25 GB/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 increases the maximum data signaling rate to 10 Gbit/s (1.25 GB/s), double that of SuperSpeed USB, and reduces line encoding overhead to just 3% by changing the encoding scheme to 128b/132b. 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 (0.500 GB/s) data signaling rate over 1 lane using 8b/10b encoding; the same as USB 3.0.
- USB 3.1 Gen 2– SuperSpeed+, new 10 Gbit/s (1.212 GB/s) data rate over 1 lane using 128b/132b encoding.
This rebranding of USB 3.0 as “USB 3.1 Gen 1” allows manufacturers to advertise products with transfer rates of only 5 Gbit/s as “USB 3.1,” omitting the generation.
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, 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 1×1– SuperSpeed, 5 Gbit/s (0.500 GB/s) data signaling rate over 1 lane using 8b/10b encoding, the same as USB 3.1 Gen 1 and USB 3.0.
- USB 3.2 Gen 1×2– SuperSpeed+, new 10 Gbit/s (1.00 GB/s) data rate over 2 lanes using 8b/10b encoding.
- USB 3.2 Gen 2×1– SuperSpeed+, 10 Gbit/s (~1.212 GB/s) data rate over 1 lane using 128b/132b encoding, the same as USB 3.1 Gen 2.
- USB 3.2 Gen 2×2– SuperSpeed+, new 20 Gbit/s (~2.4 GB/s) data rate over 2 lanes using 128b/132b encoding.
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. Similarly, at SS+ rate the encoding is 128/132, so transmission of 16 bytes physically takes 16.5 bytes, or 3% overhead. Therefore the byte-rate at SS+ is 1.25 * 0.97 GB/s = 1.212 GB/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.
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 1.6 GB/s.
USB 3.2 is supported with the default Windows 10 USB drivers and in Linux Kernel 4.18.