USB compatibility

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The developers of USB have launched a number of different versions over the years, usually accompanied by improvements in data transfer speeds, charging capabilities and other specifications.

For the USB Type B plug, the new versions came with subtle but important changes in shape which prevented them being used with earlier versions.

Fortunately, all the USB Type A designs (the classic shape that most people think of when imagining a USB plug) are ‘backwards compatible’ — meaning the USB plug can still fit into old Type A ports, and vice versa.

However, physical compatibility does not guarantee that the device will charge at the highest power or transfer data at the fastest speed.

The following page will clarify some of the confusion surround USB compatibility.

Which USB types are we comparing?

The first version of USB was launched in 1996. USB 1.0, and later USB 1.1, offered speeds of 12 Mbit/s. Since there are few, if any, computers in use that feature USB 1.0/1.1 we will ignore this version. However, all subsequent USB Type A plugs (right up to USB 3.2) still conform to the same basic rectangular shape of the original USB 1.0 Type A port and therefore can be used in the old USB 1.0 port, and vice versa.

We will consider the compatibility of the following versions:

Version Description Transfer speed

USB 2.0

The standard USB from 2000 until 2008. Many older computers feature USB 2.0 ports.

480 Mbit/s

USB 3.0

The first USB to feature the new SuperSpeed capability.

5.0 Gbit/s

USB 3.1

Introduced a data transfer speed equal to those achieved with an Ethernet cable.

10 Gbit/s

USB 3.2

The latest USB version designed to work with Type C cables to deliver SuperSpeed+ capabilities.

20 Gbit/s

USB 3.1 Gen 1 and Gen 2

There is understandably some confusion over what is meant by the following terms:

  • USB 3.0
  • USB 3.1 Gen 1
  • USB 3.1 Gen 2

The confusion arose after the creators of USB 3.0 decided to rename it USB 3.1 Gen 1 while simultaneously introducing a new SuperSpeed transfer rate of 10 Gbit/s under the name: USB 3.1 Gen 2.

Because the specifications for the new USB 3.1 Gen 1 are the same as those for USB 3.0, on this page we will simply refer to anything brought out under the name of either USB 3.0 or USB 3.1 Gen 1 as USB 3.0, while USB 3.1 Gen 2 will be called USB 3.1.

To clarify:

USB 3.0 = either USB 3.0 or USB 3.1 Gen 1

USB 3.1 = USB 3.1 Gen 2

Physical compatibility

One of the most user-friendly aspects of USB is that its primary shape — the Type A rectangle — is backwards compatible with all earlier versions. This means USB Type A plugs released under versions 3.0/3.1/3.2 will fit into old 2.0 ports and vice versa.

In most cases, plugs belonging to new versions of Type B, mini and micro will not fit into older ports.

The following table outlines the physical compatibility of the various USB versions:

Plug Receptacle

Type A 2.0

Type A 3.0

Type A 3.1

Type A 3.2

Type B 2.0

Type B 3.0

Type B 3.1

Type B 3.2

Type AB Micro 2.0

Type B Micro 2.0

B Micro 3.0/ 3.1/ 3.2

Type C

Type A 2.0













Type A 3.0













Type A 3.1













Type A 3.2













Type B 2.0













Type B 3.0













Type B 3.1













Type B 3.2













Type A Micro 2.0













Type B Micro 2.0













B Micro 3.0/3.1/3.2













Type C













Transfer speeds

Almost every new version of USB brought with it improved data transfer speeds. The backwards compatibility of the physical plugs and ports may mean that older versions can be used with newer equipment. However, achieving the latest speeds will not be possible if the host (PC or laptop), USB port, peripheral (keyboard, mouse etc.) or cable is not the latest version.

Rule of thumb

The best way to understand compatibility is to remember that your data transfer speed will always be the maximum speed that the oldest version of your equipment can achieve.

For example, if you are using a computer with USB 3.1 ports connected to a hard drive using a USB 2.0 cable, the data transfer speed will only be equivalent to the speed USB 2.0 provides.

Equally, if you have a USB 3.1 computer and a USB 3.1 webcam, but the webcam is connected via a USB 3.0 hub, you will have 3.0 speeds.

Power delivery

As well as increased data transfer speeds, each version usually comes with greater charging capacity. Recent times have seen a huge growth in devices that can charge via USB, with all smartphones now sold with a USB charging cable.

This has culminated in the new USB Power Delivery specification, which has increased the power available from 4.5W (900mA and 5V) to 100W (5A and 20V). However, as with the data speeds, this is only possible if the appropriate cable (PD-aware) is used alongside the correct type of port.

Related content

USB data transfer guide

Identifying your USB connector