Despite the name, USB, or Universal Serial Bus, has a far from universal product stack. There are multiple different connectors, protocol levels and maximum speeds. The exact differences between different versions can be hard to understand – however, it isn’t as complicated as it might seem at a glance.
USB connectors
USB 2.0 (the kind you’re most likely using for devices older than a few years) specifies six standard connectors; A, B, and then both a Mini and Micro version of each. USB 3.0 simplifies this down to three connectors that are all backwards compatible with their previous counterparts. The primary advantage (and difference) of USB 3.0 over USB 2.0 is the increased speed. USB 2.0 was able to transmit data at a maximum speed of 480Mb/s while the USB 3.0 connectors can reach speeds of up to 5Gb/s. Other advantages include the reduced number of connector standards and backwards compatibility.
The Type-A connector is the standard rectangular one that everyone should recognize when they see a ‘USB stick’. It’s typically used for devices such as USB memory sticks, cable-to-socket connectors and data transfer cables. The USB 2.0 connector has 4 connector pins, the USB 3.0 version increases this to 9, allowing faster speeds but supporting full compatibility.
The Type-B connector is much more square in appearance, with the top two corners angled for USB 2.0. Type-B connectors are typically used for devices such as printers. In USB 3.0 the top of the connector has been redesigned to be taller to add five new pins. The redesign means that USB 3.0 Type B cables cannot fit in USB type 2.0 ports. USB 2.0 cables are, however, capable of fitting in USB 3.0 connectors.
The Micro-B connector is a much flatter rectangle than the Type-A connector and has two angled corners at the top. The Micro-B connector was typically used in mobile devices such as phones and tablets, however more recently, the USB-C connector is used instead. In the USB 3.0 specification, the connector for Micro-B has been redesigned to add an extra block to the side of the connector with five extra pins. The redesign of the physical connector means than USB 3.0 cables are unable to use USB 2.0 ports, however, USB 2.0 cables can use USB 3.0 ports.
The Mini-A, Mini-B and Micro-A connectors were all discontinued in the USB 3.0 specification as they were rarely used at all.
USB 3.1 and 3.2
The USB 3.1 and 3.2 both add support for even faster data transfer speeds with the same connectors. The naming schemes, however, are decidedly confusing and have lead to less reputable sellers using vague naming to imply their products offer top speeds when they really run slower than that.
USB 3.1 renames the original USB 3.0 connection to USB 3.1 Gen 1. No changes were made, it was just rebranded. A second faster speed was also standardized called USB 3.1 Gen 2 – it allowed for double the transfer speeds, at up to 10 Gb/s.
USB 3.2 renames the two modes from USB 3.1 to USB 3.2 Gen 1×1 and USB 3.2 Gen 2×1 respectively. It also allows for two new modes that use two previously unused pins to transmit twice the data. These are referred to as USB 3.2 Gen 1×2 and USB 3.2 Gen 2×2.
USB 3.2 Gen 1×2 runs at essentially the same 10 Gb/s as USB 3.2 Gen 2×1. USB 3.2 Gen 2×2 offers double the speed at 20 Gb/s.
Tip: To summarise: USB 3.1 and 3.2 use the same physical connector shapes, however more recent versions such as the Gen2x2 offer higher data transfer speeds than USB 3.0.
USB Type-C
The USB Type-C connector was developed by the USB Implementers Forum independently of the development of earlier USB protocols. It addresses a common complain about USB connectors in that the connector is reversible, meaning you no longer have to try multiple times to get the cable the right way around. You’re probably familiar with the pain of having to flip a USB stick 3+ times until it fits – USB-C eliminates this, while also being smaller and thus more versatile, for example for use in ultra-flat smartphones.
USB Type-C connectors are backwards compatible with USB 2.x and 3.x when using an adaptor to fit the physical socket. The newest USB protocol, USB 4.0 which was standardised in August 2019, requires the use of the USB Type-C connector and offers speeds of up to 40 Gb/s, with support for at least 20 Gb/s being required.
Yes, very useful, thanks.