Understanding USB-C, USB-B and USB-A ports

This article provides a good overview of the most popular USB ports and connectors in the market. It helps you understand USB-C (or USB Type-C), USB-B (or USB Type-B) and USB-A (or USB Type-A) ports. We also discuss some basic information on each of the USB type’s features, compatibility and provide technical details on the USB versions available, their supported speeds, current, voltage and wattage.

What is USB?

USB stands for Universal Service Bus. USB was originally intended to be a data transfer standard between computers and their peripherals. Later, it was expanded and adopted by numerous manufacturers for electronic devices such as mobile phones, digital cameras, gaming consoles, TVs, etc.

USB Implementers Forum, Inc., better known as USB-IF has developed the USB standard. USB-IF is a consortium of some of the top companies in the industry which produce electronics products, such as Apple, HP, Intel and Microsoft, among others. For more detailed technical information, you may visit their official website.

While it is debatable on how universal it has been in the past decades, USB-IF has done an excellent job with the standard. The standard is now the most popular connection mechanism and has truly become universal. Manufacturers of electronic devices have started adopting and implementing the standard on various devices. Today, it is hard to find an electronic device without a USB port. Consumers making a purchase decision should pay attention to the USB connector type (USB-A, USB-B, USB-C, etc.) and the version (2.0, 3.0, 3.2, etc.) implemented on an electronic device.

Terminology

Before we go too deep into the weeds, lets make sure we understand some basics on USB. Some of these terms are used differently by other sources, but we will use common industry definitions.

  • A connector is usually a cable that ends with a metal structure that we plug into a device’s port. A connector is usually male.
  • A port is usually a female on a device such as a laptop or a phone.
  • There are female connectors that accept a male connector to extend the cord.
  • USB Specification (or USB Version) is a standard defined and published by USB-IF. Manufacturers of electronic devices with USB port implement one of the USB specifications.

What is USB Type-C?

At the time of this writing (December 2024), USB Type-C is the most popular USB connector/port standard with most new products such as mobile phones, laptops, and other electronic devices supporting/implementing USB-C. Note that USB-C is another popular term for USB Type-C and we will use them interchangeably throughout this article.

Physical characteristics

USB Type-C has an elongated oval shape and it is physically symmetrical, which means you can plug it in anyway. USB-C is relatively thinner and designed for modern and slim devices like laptops, smartphones, etc.

USB Type-C

USB-C Features

The most basic feature of USB Type-C is data transfer. However, USB-C has become standard connector or port to deliver power to charge portable devices like smartphones, laptops, etc. Additionally, a USB-C can also be used to transmit video/audio and connect a laptop to a display device.

USB-C Data transfer speeds

Different versions of USB-C implementations support different speeds. It is currently not possible to look at a USB-C port and tell the speed at which it operates. Note that to transfer data at a given speed, everything in the chain of the data transfer – the port, the connector and the cable – need to support the speed we need.

USB-C Power delivery

Older USBs have capabilities to transfer a small amount of current, but the newer USB Type-C has the capability to transfer up to 240W, enough to charge powerful laptops. The USB PD (power delivery) specification released by USB-IF has made this possible. The implementation of this specification in ports and devices allows consumers to use USB-C to power larger devices.

At the time of this writing, the latest version of USB PD spec is revision 3.1(which is not the same as USB 3.1). This has pushed the boundaries of power delivery of USB to 240W. While it is best to ensure that the connector and port support the minimum power required by the device being charged, using an adapter is ideal to regulate the power delivery correctly and prevent damage to the devices. For more details see the official USB PD page.

USB-C compatibility

One would think that as long as the hardware connector/port are physically compatible, everything should just work, right? Wrong! Not all USB-C ports or connector cables are created equal. This is because different USB-C ports/connectors may implement different versions of the standard. Which means, you can have a computer with a USB-C port that may support version 2.0 and a webcam connected to that port, which may support USB 3.0. Physically, they are compatible, i.e., the connector cable fits into the port, but the features available will be that of the lowest version, i.e., 2.0. So the data transfer rate, power delivery, etc. will be of 2.0 spec.

The various versions available on USB-C port currently are USB 2.0, 3.0, 3.1, 3.2 and newest USB 4.0. These versions have differences in speeds and power delivery capabilities.

What is USB Type-A?

USB-A (or USB Type-A) is one of the older versions of USB and was the most popular USB type until recently, however USB-C has gained more popularity and acceptance due to its data transfer speed and power delivery capabilities. Hence, if you are considering buying a computer you might want to make sure you have this port. Today, most common devices using this port are flash drives, keyboards, mice, printers, TVs, etc. But if you are purchasing a laptop or any other electronic device, you really should give preference to USB-C port.

Physical Characteristics

USB-A port or connector is rectangular in shape with a blue, white or black tongue. A USB-A connector can only be plugged in one way only unlike the newer USB-C connector.

USB Type-A

USB-A Features

A USB-A connector’s main purpose is data transfer. Just like any other USB type, depending on the connector a Type-A may implement one of the number of USB specifications or versions. The speed at which data transfer can happen depends on the USB spec version implemented by the connector. The maximum speed USB Type-A can support is 10Gbps. It does transfer a small amount of power as well, again depending on the USB version implemented.

USB-A Compatibility

As long as a USB-A port and connector physically fit, the basic feature such as data transfer should work. Again, a connection between a device and a port operates at the lowest supported version. To understand the exact data transfer speed capability, current, wattage and volts, you’ll need the USB spec version implemented. Please see the compatibility table below for more details.

What is USB Type-B?

USB Type-B was designed primarily for data transfer, but it can transfer a small charge as well. This is not very popular and is not designed to be a port to maximize compatibility and support. So, if you are purchasing an electronic product, you really shouldn’t care about this type of port, unless you have a special use case or need. This type of connector is most common in old printers or other older devices.

Physical Characteristics

A USB Type-B port is non-symmetrical, which means it can only be plugged in one way. There is something interesting and unique about USB Type-B connectors in that there are two physically different USB-B connectors such as:

  1. 1.1/2.0 connector
  2. 3.0 connector

USB Type-B 1.1/2.0 connector has a square-shape with top two corners flattened, like below:

USB Type-B v1.1 or V2.0

USB Type-B 3.0 connector looks like USB Type-B 1.1/2.0 with a smaller square extension on top like below:

USB Type-B 3.0

Image source: eu.shi.com

Note that physically USB 1.1/2.0 connector should fit into USB 3.0 port as well, although it will be limited to USB 1.1/2.0 spec. However the USB 3.0 connector will NOT fit into USB 1.1/2.0 port.

USB-B Features

USB-B is one of the older connectors and some old devices with USB-B ports support USB 1.0. At the time of this writing, the newest version USB-B can support is 3.2. Since most manufacturers moved on to either USB-A or USB-C, it is not easy to find a USB-B that supports 3.2. Use the table below to find the speeds and power transfer supported for your USB-B port/connector but you will need to know the USB spec version implemented.

USB-B Compatibility

Other than the physical compatibility limitation upwards between the two USB-B connectors, there is nothing special. Similar to other USB types, they are generally backward compatible as long as they are physically compatible. However the data transfer speed or power will fall back to the lowest USB spec in the connection.

USB versions, speeds and maximum current.

USB Spec StandardSpeedOfficial NameConnectors supportedMax. WattageMax. VoltsMax. Current
USB 1.01.5 MbpsLow SpeedUSB-A (USB Type-A)
USB-B (USB Type-B)
2.5W5V500 mA
USB 1.112 MbpsFull SpeedUSB-A (USB Type-A)
USB-B (USB Type-B)
2.5W5V500 mA
USB 2.0480 MbpsHigh SpeedUSB-A (USB Type-A)
USB-B (USB Type-B)
USB Micro-A
USB Micro-B
USB Mini-A
USB Mini-B
USB-C (USB Type-C)
2.5W5V500 mA
USB 3.05 GbpsSuperSpeed
or USB 5 Gbps
USB-A (USB Type-A)
USB-B (USB Type-B)
USB Micro-A
USB Micro-B
USB-C (USB Type-C)
4.5W5V900 mA
USB 3.1 Gen 1,
USB 3.2 Gen 1
5 GbpsSuperSpeed
or USB 5 Gbps
USB-A (USB Type-A)
USB-B (USB Type-B)
USB-C (USB Type-C)
4.5W5V900 mA
USB 3.1 Gen 2
USB 3.2 Gen 2
10 GbpsSuperSpeed+
or SuperSpeed 10 Gbps
or USB 10 Gbps
USB-A (USB Type-A)
USB-B (USB Type-B)
USB-C (USB Type-C)
100W
(with USB PD)
20V
(with USB PD)
5A
(with USB PD)
USB 3.2 Gen 2×220 GbpsSuperSpeed 20 Gbps
or USB 20 Gbps
USB-C (USB Type-C)100W
(with USB PD)
20V
(with USB PD)
5A
(with USB PD)
USB 4.0 or USB440 GbpsUSB 40 GbpsUSB-C (USB Type-C)240W48V5A
USB4 Version 280 GbpsUSB 80 GbpsUSB-C (USB Type-C)240W48V5A
USB Battery Charging (USB BC)N/AN/AUSB-A (USB Type-A)
USB-B (USB Type-B)
USB-C (USB Type-C)
7.5W5V1.5A
USB-C non-PD (power delivery)N/AN/AUSB-C (USB Type-C)15W5V3A
USB-C PD (power delivery)N/AN/AUSB-C (USB Type-C)240W48V5A
NOTES:
1. The above table shows what’s supported for a given USB spec but manufacturers can choose to support a specific spec which may always be the highest spec for the port or connector in question.
2. When two devices are connected through a cable, an adapter, and the connector types on either side of the cable, the lowest USB spec version supported in this chain will apply. For example, if we connect a laptop to an external storage with a USB-A connector (implementing USB spec 2.0) to USB-C connector (implementing USB spec 3.0), the data transfer speeds of USB 2.0 will apply.

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