USB standards and connectors

Although most people are familiar with the USB standard, there tends to be some confusion regarding the USB naming system. In this article, we will discuss the differences between USB standards, name revisions and connector types to clear up some of the confusion surrounding USB nomenclature.


USB (Universal Serial Bus) is a standard established for cables, connectors and protocols that are used for communication and power delivery between computers and peripherals. The USB standards are defined by the USB-IF (Universal Serial Bus Implementer’s Forum), which regulates the requirements for each standard and oversees the naming process. To date, there have been four major generations of USB standards.

USB Standards


First two generations

The naming system for the earlier generations of USB standards was fairly straightforward. The first generation of USB was launched as USB 1.0 in 1996. USB 1.0 featured transfer rates of 1.5 Mbps but was not widely adopted until a revision to the standard (USB 1.1) introduced 12 Mbps speeds.

USB 2.0 was released in 2000, vastly speeding up the transfer rates to 40x that of USB 1.1 at 480 Mbps. It has become one of the most widely adopted standards used by computing and connecting devices worldwide today.


Third generation

While the earlier generations had a very clear naming structure, the third generation is where the naming standards would start to deviate from the original USB nomenclature.

USB 3.0

Initially, USB 3.0 followed the naming system for USB 1.0 and USB 2.0 by adding a 3.0 moniker to indicate that it was the third-generation edition of the USB standard. It was introduced in 2008 as a full duplex connection and featured an upgraded protocol and electrical interface. With these new changes, USB 3.0 delivered 10x the transfer rate of the previous generation at 5 Gbps speeds. It was also backwards compatible with USB 2.0 and 1.1 ports.

USB 3.1

Things would get a bit interesting when USB-IF launched a new standard that doubled transfer rates to 10 Gbps in 2013. While the expectation at the time was that it would be named USB 4.0, it was instead named USB 3.1.

Now normally, this wouldn’t be much of a cause for confusion. There was already some precedence for this naming pattern when USB 1.1 was released as an update to USB 1.0. What made things confusing, however, was that a full name revision was subsequently made to both the 3.0 and 3.1 standards. USB 3.0 was retroactively changed to USB 3.1 Gen 1 while the new USB 3.1 standard was renamed USB 3.1 Gen 2, as shown below.

First naming scheme change:

Old Name New Name
USB 3.0 USB 3.1 Gen 1
USB 3.1 USB 3.1 Gen 2

USB 3.2

To further complicate things, another new standard was released in 2019 and it doubled transmission speeds to a rate of 20Gbps. Going by the naming logic of the first revision, one would expect the new standard to be named USB 3.1 Gen 3. In true USB naming fashion, however, that was not the case. Because USB 3.2 introduces dual lane operation, USB-IF added a “x2” denotation to the new standard to indicate its support for two lanes.

Adding to the chaos, the USB-IF made another retroactive revision to the older naming schemes. A “x1” denotation was affixed to the labels of single lane USB 3.1 Gen 1 and USB 3.1 Gen 2 while a “x2” was added to dual lane USB 3.1 Gen 1 and USB 3.1 Gen 2. To top it all off, all third generation USB standards were also changed from USB 3.1 to 3.2 as shown below:

Second naming scheme change:

Old Name New Name
USB 3.1 Gen 1 USB 3.2 Gen 1x1
USB 3.1 Gen 2 USB 3.2 Gen 2x1
USB 3.2 USB 3.2 Gen 1x2 or USB 3.2 Gen 2x2

Although these name changes were likely implemented to differentiate between the standards, the new changes may have inadvertently introduced more confusion by revising names not once, but twice. It’s a huge reason why to this day, there is still a great deal of confusion for many users regarding the naming system!

Fourth generation

The fourth generation of USB finally brought back some normality. USB 4.0 was released in 2019 and delivered speeds of 40Gbps. The newest standard was designed to work with USB Type-C connectors exclusively. The standard supports tunneling of USB 3.2, DisplayPort, as well as PCIe devices, meaning that it’s able to take a signal and convert it into packets that can be sent via the USB Type-C cable simultaneously, with multiple types of data.

So, for those keeping score, the following chart summarizes the naming scheme (and their revisions) and transfer rates for all generations of USB to date:

Specification First Change Second Change Transfer Rate
USB 1.0 - - 12 Mbps
USB 1.1 - - 12 Mbps
USB 2.0 - - 480 Mbps
USB 3.0 USB 3.1 Gen 1 USB 3.2 Gen 1x1 5 Gbps
USB 3.1 USB 3.1 Gen 2 USB 3.2 Gen 2x1 10 Gbps
USB 3.2 - USB 3.2 Gen 2x2 20 Gbps
USB 4.0 - - 40 Gbps

USB Connectors

Now that we’ve discussed the standards, let’s take a closer look at USB connectors, which are a different altogether from USB standards. Standards are designations that indicate the specifications of which USB devices must meet. USB connectors are the plugs that are slotted into compatible receptacles to connect peripherals to computing devices.

There are three main USB connector types:


Type-A connectors are by far the most commonly used USB connectors. The easily recognizable, elongated rectangular plug comes with a four-pin design, which has been in use since the launch of the first-generation USB standard. Type-A connectors can carry both data as well as power. They are usually color coded to indicate the versions as well as their functions.

Although the third generation of USB easily has the most confusing nomenclature, most USB 3.2 series connectors will have a blue outline on the slot itself. This isn’t standardized by USB-IF, however, so it’s more common etiquette for manufacturers as opposed to an actual requirement.


Type-B connectors are less commonly found on computers/laptops and instead are primarily used on printers and hard drives. The squarish shaped with sloped edges connector also comes with a four-pin design. As is the case with Type-A, there are an assortment of mini connectors, including Type mini-A, Type mini-B, Type micro-A, and Type Micro-B that support a number of larger peripheral devices. Type-B also comes with various color designations.


Type-C connectors are the newest USB connectors. They feature a much different design from its predecessors. Slimmer and more compact, the newest 24-pin connector is used on a wide assortment of newer computing devices. A new feature of Type-C that differentiates it from its predecessors is that the new connector is reversible, meaning it is symmetrical and can be plugged in regardless of its top/down orientation. Type-C connectors also have higher durability ratings than its predecessors, offering 10,000 insertion cycles.


Count on Axiom Upgrades

Axiom supports USB devices from all generations and standards as well a multitude of connector types. Axiom solutions such as Axiom’s 12-in-1 adapter offers four USB slots which support multiple USB connector types and standards. With the 12-in-1 adapter, users can connect compatible devices through the USB Type-C 24-pin connector and leverage the USB 3.0 bus interface for more efficient data transfer at transmission speeds of up to 5Gbp/s. Users are able to connect a diverse assortment of peripherals to the dual USB 3.0 ports, which also have backwards compatibility with USB 2.0 devices. The hub also comes with a classic USB 2.0 slot which provides stable and reliable transmission speeds.

Axiom is a leading provider of third-party upgrades in server and data center hardware. With a cost-effective approach for our customers, businesses are able to retool data centers to address key IT needs. To learn more about how Axiom third-party upgrades can optimize your servers and data centers, contact an Axiom sales representative or visit our website for more details at