Everything you need to know about Universal Serial Bus, aka USB
USB, short for Universal Serial Bus, is a standard type of connection for many kinds of devices. Generally, USB refers to the types of cables and connectors used to connect these many types of external devices to computers.
What is USB?
The Universal Serial Bus standard has been extremely successful. USB ports and cables are used to connect hardware such as printers, scanners, keyboards, mice, flash drives, external hard drives, joysticks, cameras, monitors, and more to computers of all kinds, including desktops, tablets, laptops, netbooks, etc.
In fact, USB has become so common that you'll find the connection available on nearly any computer-like device such as video game consoles, home audio/visual equipment, and even in many automobiles.
Before USB, many of those devices would attach to a computer over serial and parallel ports, and others like PS/2.
Many portable devices, like smartphones, eBook readers, and small tablets, use USB primarily for charging. USB charging has become so common that it's now easy to find replacement electrical outlets at home improvement stores with USB ports built in, negating the need for a USB power adapter.
USB Versions
There have been several major USB standards, USB4 being the newest:
- USB4: Based on the Thunderbolt 3 specification, USB4 supports 40 Gbps (40,960 Mbps).
- USB 3.2 Gen 2x2: Also known as USB 3.2, compliant devices are able to transfer data at 20 Gbps (20,480 Mbps), called Superspeed+ USB dual-lane.
- USB 3.2 Gen 2: Previously called USB 3.1, compliant devices are able to transfer data at 10 Gbps (10,240 Mbps), called Superspeed+.
- USB 3.2 Gen 1: Previously called USB 3.0, compliant hardware can reach a maximum transmission rate of 5 Gbps (5,120 Mbps), called SuperSpeed USB.
- USB 2.0: USB 2.0 compliant devices can reach a maximum transmission rate of 480 Mbps, called High-Speed USB.
- USB 1.1: USB 1.1 devices can reach a maximum transmission rate of 12 Mbps, called Full Speed USB.
Most USB devices and cables today adhere to USB 2.0, and a growing number to USB 3.0.
The parts of a USB-connected system, including the host (like a computer), the cable, and the device, can all support different USB standards so long as they are physically compatible. However, all parts must support the same standard if you want it to achieve the maximum data rate possible.
USB Connectors
A number of different USB connectors exist, all of which we describe below.
The male connector on the cable or flash drive is typically called the plug. The female connector on the device, computer, or extension cable is typically called the receptacle.
- USB Type C: Often referred to simply as USB-C, these plugs and receptacles are rectangular with four rounded corners. Only USB 3.1 Type C plugs and receptacles (and thus cables) exist, but adapters for backward compatibility with USB 3.0 and 2.0 connectors are available. This latest USB connector has finally solved the problem of which side goes up. Its symmetrical design allows it to be inserted in the receptacle in either fashion, so you never have to try again (one of the biggest peeves about earlier USB plugs). These are being widely adopted on smartphones and other devices.
- USB Type A: Officially called USB Standard-A, these plugs and receptacles are rectangular and are the most commonly seen USB connectors. USB 1.1 Type A, USB 2.0 Type A and USB 3.0 Type A plugs and receptacles are physically compatible.
- USB Type B: Officially called USB Standard-B, these plugs and receptacles are square shaped with an extra notch on top, most noticeable on USB 3.0 Type B connectors. USB 1.1 Type B and USB 2.0 Type B plugs are physically compatible with USB 3.0 Type B receptacles but USB 3.0 Type B plugs are not compatible with USB 2.0 Type B or USB 1.1 Type B receptacles.
- A USB Powered-B connector is also specified in the USB 3.0 standard. This receptacle is physically compatible with USB 1.1 and USB 2.0 Standard-B plugs, and of course, USB 3.0 Standard-B and Powered-B plugs as well.
- USB Micro-A: USB 3.0 Micro-A plugs look like two different rectangular plugs fused together, one slightly longer than the other. USB 3.0 Micro-A plugs are only compatible with USB 3.0 Micro-AB receptacles.
- USB 2.0 Micro-A plugs are very small and rectangular, resembling in many ways a shrunken USB Type A plug. USB Micro-A plugs are physically compatible with both USB 2.0 and USB 3.0 Micro-AB receptacles.
- USB Micro-B: USB 3.0 Micro-B plugs look almost identical to USB 3.0 Micro-A plugs in that they appear as two individual, but connected, plugs. USB 3.0 Micro-B plugs are compatible with both USB 3.0 Micro-B receptacles and USB 3.0 Micro-AB receptacles.
- USB 2.0 Micro-B plugs are very small and rectangular, but the two corners on one of the long sides are beveled. USB Micro-B plugs are physically compatible with both USB 2.0 Micro-B and Micro-AB receptacles, as well as USB 3.0 Micro-B and Micro-AB receptacles.
- USB Mini-A: The USB 2.0 Mini-A plug is rectangular, but one side is more rounded. USB Mini-A plugs are only compatible with USB Mini-AB receptacles. There is no USB 3.0 Mini-A connector.
- USB Mini-B: The USB 2.0 Mini-B plug is rectangular with a small indention on either side, almost looking like a stretched out piece of bread when looking at it head-on. USB Mini-B plugs are physically compatible with both USB 2.0 Mini-B and Mini-AB receptacles. There is no USB 3.0 Mini-B connector.
Just to be clear, there are no USB Micro-A or USB Mini-A receptacles, only USB Micro-A plugs and USB Mini-A plugs. These "A" plugs fit in "AB" receptacles.
USB Troubleshooting
Using a USB device is usually pretty straightforward: just plug it in. Unfortunately, it's not always that simple.
Some brand-new USB-connected hardware need special device drivers to fully function. Other times, a USB device that's been working normally for years might suddenly stop working without an obvious reason why.