USB versions & transfer speeds explained!

USB (Universal Serial Bus) is a common type of port that’s widely used for a variety of devices. These include phone charging, data transfer, external storage devices, webcams, microphones, keyboards, mice and much more.

There are many versions of USB standards, and it may seem a little overwhelming when trying to understand USB standards and their specifications, especially after so many revisions by the USB-IF (USB Implementers Forum). In this article, we will explain the differences of each USB revision as well as other information that may be helpful to you.


Examples of SilverStone products that utilizes USB technology: Left – MS12, Right – EP14

MS12
EP14

USB

USB 1.0 released in January 1996 had specific bandwidth speed of 1.5 Mbps, it did not have wide adoption due to its timing and power limitations. It wasn’t until the release of USB 1.1 in August 1998, which increased bandwidth to 12 Mbps, that it became popular.

Released in April 2000, USB 2.0 debuted shortly after USB 1.1; this version of USB standard saw an increase in maximum signal bandwidth speed to 480Mbps and was labeled High Speed – it was 40 times faster than its USB 1.1 predecessor. USB 2.0 was intended for 3 applications; digital storage, digital imaging and communications, which stood the test of time and was the most widely adopted USB to date.

Later on, USB 2.0 was also being used for charging devices rather than simply transferring data between devices, thus completely changing the landscape of the technology as USBs are now being used outside of its initial intended applications.


USB 3.2

You might be wondering why the title says USB 3.2 and not USB 3.0, well this is where it gets tricky!

The USB 3.0 specification was released on November 2008 with a maximum bandwidth speed of 5Gbps; labeled as SuperSpeed which is about 10 times faster than the USB 2.0 standard. As the third major version to be added to the USB standards, not only did it see an increase in speed, but to differentiate from USB 2.0, manufacturers were recommended to use blue colored connectors for the Standard-A receptacles and plugs.

A new revision was released in 2013, named USB 3.1 which was to include a new version that doubled the speed of the original from 5Gbps to 10Gbps. This is where the confusion began for a lot of people.

At the time of USB 3.1 release, USB-IF also decided to rename the original USB 3.0 specification, changing from original USB 3.0 to USB 3.1 Gen 1 and adding the new version as USB 3.1 Gen 2.

Original Bandwidth speed Renamed
USB 3.0 5Gbps USB 3.1 Gen 1
- 10Gbps USB 3.1 Gen 2

Making matters worse, another revision was released in September 2017 which doubled the speed again to 20Gbps over USB-C connectors by utilizing dual data lane operation. You’d think that the 20Gbps variation under the new naming scheme would be called USB 3.1 Gen 3, which wasn’t the case as USB-IF decided to change the names once again, resulting in USB 3.1 Gen 1 as USB 3.2 Gen 1, USB 3.1 Gen 2 as USB 3.2 Gen 2, and the new 20Gbps revision as USB 3.2 Gen 2x2.

Original Bandwidth speed Renamed Renamed again
USB 3.0 5Gbps USB 3.1 Gen 1 USB 3.2 Gen 1
- 10Gbps USB 3.1 Gen 2 USB 3.2 Gen 2
20Gbps USB 3.2 Gen 2x2

USB4

USB4 is the most recent version of the USB standard released in August 2019, which is based on the Thunderbolt 3 protocol. The main characteristics of USB4 includes a maximum bandwidth speed of 40Gbps, USB PD, protocol tunneling and backward compatibility.

40Gbps bandwidth speed – By utilizing dual-lane operation, USB4 can reach a maximum speed of 40Gbps throughput and mandatory 20Gbps throughput operating over USB-C connector.

Thunderbolt 3 protocol – Allows (some, but not all) devices with USB4 ports to be compatible with Thunderbolt 3 devices, and vice versa. Great news for users with Thunderbolt 3 laptops who are looking for an eGPU solution.

USB PD (Power Delivery) – All USB4 devices must comply with USB PD, which allows for higher wattages and better power management.

Protocol tunneling – USB4 allows for protocol tunneling of USB bus architecture for USB 3 (Enhanced SuperSpeed tunneling), DisplayPort (display tunneling), and PCI Express, aggregating different protocols in order to share bandwidth between them. These protocol tunnels operate independently over the USB4 transport and physical layers.

Backward compatibility – USB4 is backwards compatible with USB 3.2, USB 2.0 and Thunderbolt 3.

Even though USB4 can hit a theoretical speed of up to 40Gbps, not all USB devices and hosts supports this standard, but soon, it will become available in consumer products and become the standards in the near future. So for now, expect small devices such as phones and different gadgets to use the 20Gbps version of USB4.