A Basic Guide to USB

By Ashley Awalt

Contributed By Digi-Key Electronics

What is USB (Universal Serial Bus)? USBs are rectangular-shaped connectors used for data transfer and power administration. They are most commonly used for charging devices or transferring data from a storage device to a viewing device. USBs were originally created to help simplify the connection of computers with peripheral devices.

The female connector (receptacle) is typically embedded into a device while the male connector (plug) is generally free-hanging so it can be placed on the end of a cable assembly for two or more devices to be interconnected at a time.

USB versions

USB 1.0 was introduced in 1996. Not many were utilized in new products until 1998 when USB 1.1 was released. This version only included standard A and B type connectors. At this point, with a speed of 12 Mbit/s, USB 1.1 was becoming more widely adopted.

USB 2.0 boasted a speed of 480 Mbit/s when it was released in 2000, the same year the Mini-A and Mini-B connector types were released. After many upgrades and improvements, including battery charging capabilities, the Micro USB connector type was released in 2007.

USB 3.0, released in 2008, also came with the new SuperSpeed transfer mode that reached a signaling rate of 5 Gbit/s. The SuperSpeed connectors are marked with a special logo while the standard receptacles have blue inserts to help identify those capabilities.

USB 3.1 was revealed in 2013 to upgrade the speed to 10 Gbit/s, thus passing the original SuperSpeed transfer mode. The new logo to distinguish this from the old SuperSpeed is SUPERSPEED+.

Connector types

There are quite a few styles of USB connectors; the images and descriptions below will go over the most common types.

Type A (Figure 1): This is the most commonly utilized USB style. It is found in a multitude of places such as: computers, flash drives, cars, wall converters, etc. This type has four contact points, two for data and two for negative and positive power. They are all positioned alongside each other. 

Image of male/plug and female/receptacle USB Type A connectors

Figure 1: Male and female USB Type A connectors.

Type B (Figure 2): This style of USB was designed for peripheral device connection to computers. Peripheral device examples include keyboard, mouse, scanner, etc. This type has four contact points, just like Type A. Two are for data and two for negative and positive power. Two are positioned on the top, and two on the bottom.

Image of male/plug and female/receptacle USB Type B connectors

Figure 2: Male and female USB Type B connectors.

Type Mini A (Figure 3): This is not one of the more commonly used styles. This type has five contact points. All positioned in a straight line. 

Image of male/plug and female/receptacle USB Type Mini A connectors

Figure 3: Male and female USB Type Mini A connectors.

Type Mini B (Figure 4): This style was previously used in cell phones for charging capabilities. This type has five contact points. All positioned in a straight line.

Image of male/plug and female/receptacle USB Type Mini B connectors

Figure 4: Male and female USB Type Mini B connectors.

Type Micro A (Figure 5): The Micro A is not as common as the Micro B. This type has five contact points. All positioned in a straight line.

Image of male/plug USB Type Micro A connector

Figure 5: Male USB Type Micro A connector.

Type Micro B (Figure 6): This style is very common. It is currently used for most major cell phone charging connectors. This type has five contact points. All positioned in a straight line.

Image of female/receptacle and male/plug USB Type Micro B connector

Figure 6: Female and male USB Type Micro B connector.

Micro B SuperSpeed (Figure 7): This is becoming more popular as it claims to have faster data transfer and charging rates. This type has 10 contact points, five in the standard Micro B portion and 5 in the additional portion. This receptacle is backwards compatible with all Micro B plugs.

Image of male/plug and female/receptacle USB Type Micro B SuperSpeed connectors

Figure 7: Male and female USB Type Micro B SuperSpeed connectors.

Type C (Figure 8): This style is reversible. It is starting to be utilized by certain phone companies due to claims of faster data and charging rates. This type has twenty-four contact points. Aside from the standard data transfer and power pins, this also has one configuration pin to determine the cable orientation.

Image of male/plug and female/receptacle USB Type C connectors

Figure 8: Male and female USB Type C connectors.

Looking for a specific USB cable assembly or connector? Digi-Key has a wide variety to offer:

USB cable assemblies

USB connectors

USB adapters

References

  1. Wikipedia USB,” last modified February 7, 2017
  2. USB Connector Guide – Guide to USB Cables,” Cables To Go, accessed February 14, 2017,

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

Ashley Awalt

Ashley Awalt is a Technical Content Developer that has been with Digi-Key Electronics since 2011. She earned her Associate of Applied Science degree in Electronics Technology & Automated Systems from Northland Community & Technical College through the Digi-Key scholarship program. Her current role is to assist in creating unique technical projects, documenting the process and ultimately participating in the production of video media coverage for the projects. In her spare time, Ashley likes to – oh, wait, is there such a thing as spare time when you’re a mom?

About this publisher

Digi-Key Electronics

Digi-Key Electronics, based in Thief River Falls, Minn., is a global, full-service provider of both prototype/design and production quantities of electronic components, offering more than six million products from over 750 quality name-brand manufacturers at Digi-Key.