USB? A Comprehensive Guide to Universal Serial Bus

by Joost Nusselder | Updated on:  May 3, 2022

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Isn’t USB just a universal standard for connecting devices? Well, not quite.

Universal Serial Bus (USB) is an industry-standard developed in the mid-1990s using communications protocols in a bus for connection. It was designed to standardize the connection of computer peripherals (including keyboards and printers) to personal computers, both to communicate and to supply electric power.

But how does it do that? And why do we need it? Let’s look at the technology and find out.

What is usb

Understanding the Meaning of Universal Serial Bus (USB)

The Standardized Connection for Devices

USB is a standardized connection that allows devices to connect to a computer or other devices. It is intended to enhance the connectivity of a wide range of devices and allow them to communicate with each other. USB is widely used in the industry and is the preferred method of connecting devices to personal computers.

Establishing Protocols for USB Devices

USB establishes protocols for devices to communicate with each other. It allows devices to request and receive data in large quantities. For example, a keyboard can send a request to the computer to type a letter, and the computer will send the letter back to the keyboard to display it.

Connecting a Range of Devices

USB can connect a wide range of devices, including media devices like hard drives and flash drives. It is also intended to allow for the spontaneous configuration of devices. This means that when a device is connected, the computer can automatically discover and configure it without the need for a restart.

The Physical Structure of USB

USB consists of a flat, rectangular connector that inserts into a port on a computer or hub. There are different types of USB connectors, including square and slanted exterior connectors. The upstream connector is usually removable, and a cable is used to connect it to the computer or hub.

USB Voltage and Maximum Bandwidth

The latest generation of USB supports a maximum voltage of 5 volts and a maximum bandwidth of 10 Gbps. The structure of USB includes the following interfaces:

  • Host Controller Driver (HCD)
  • Host Controller Driver Interface (HCDI)
  • USB Device
  • USB Hub

Managing Bandwidth and Meeting Customer Requirements

The USB protocol handles the interconnection between devices and manages the bandwidth to ensure that data is transmitted as quickly as possible. The bandwidth that is available depends on the technical specifications of the USB device. The USB software manages and controls the data flow and realizes the communication between the concealed parts of the USB.

Facilitating Data Transfer with USB Pipes

USB consists of pipes that facilitate the transfer of data between devices. A pipe is a logical channel that is used to transfer data between software and hardware. USB pipes are used to transfer data between devices and software.

The Evolution of USB: From Basic Connectivity to Global Standard

The Early Days of USB

USB devices were originally developed as a way of setting up a computer with a multitude of peripherals. In the early days, there were two basic varieties of USB: parallel and serial. The development of USB began in 1994, with the goal of fundamentally making it easier to connect PCs to a multitude of devices.

The addressing and usability issues that plagued parallel and serial connections were simplified with USB, as it allowed for software configuration of connected devices, permitting greater plug and play functionality. Ajay Bhatt and his team worked on the integrated circuits supporting USB, which were produced by Intel. The first USB interfaces were sold globally in January 1996.

USB 1.0 and 1.1

The earliest revision of USB was widely adopted, and it led to Microsoft designating USB as the standard connection method for PCs. The USB 1.0 and 1.1 specifications allowed for low bandwidth connections, with a maximum transfer rate of 12 Mbps. This was a significant improvement over parallel and serial connections.

In August 1998, the first USB 1.1 devices appeared, conforming to the new standard. However, the design was hampered by treating peripherals as tethered to the connection receptacle, which was known as the “A” connector. This led to the development of the “B” connector, which allowed for a more flexible connection to peripherals.

USB 2.0

In April 2000, USB 2.0 was introduced, adding support for higher bandwidth connections with a maximum transfer rate of 480 Mbps. This led to the development of smaller designs, such as miniaturized connectors and USB flash drives. The smaller designs allowed for greater portability and convenience.

USB 3.0 and Beyond

USB 3.0 was introduced in November 2008, with a maximum transfer rate of 5 Gbps. This was a significant improvement over USB 2.0 and allowed for faster data transfer rates. USB 3.1 and USB 3.2 were later introduced, with even higher transfer rates.

Modifications to the engineering of USB have been made over the years, with change notices and important engineering change notices (ECNs) included in the package. USB cables have also evolved, with the introduction of interchip cables that make it possible to communicate between devices without requiring a separate USB connection.

USB has also added support for dedicated chargers, which allow for faster charging of devices. USB has become a global standard, with billions of devices sold worldwide. It has revolutionized the way we connect and communicate with our devices, and it continues to evolve to meet the needs of the modern world.

USB Connector Types


USB connectors are an essential part of the USB system, providing a means of connecting USB devices to a computer or other device. There are several different types of USB connectors, each with its own specific configuration and designation.

USB Plug and Connector Types

The USB plug is the male connector that is typically found on USB cables, while the USB connector is the female receptacle found on USB devices. There are several different types of USB plugs and connectors, including:

  • Type A: This is the most common type of USB plug, typically found on USB devices such as keyboards, memory sticks, and AVR devices. It is terminated on the other end with a Type A connector that plugs into a USB port on a computer or other device.
  • Type B: This type of USB plug is typically found on USB devices that require more power than a Type A connector can provide, such as printers and scanners. It is terminated on the other end with a Type B connector that plugs into a USB port on a computer or other device.
  • Mini-USB: This type of USB plug is a smaller version of the Type B plug and is typically found on digital cameras and other small devices. It is terminated on the other end with a Type A or Type B connector that plugs into a USB port on a computer or other device.
  • Micro-USB: This type of USB plug is even smaller than the Mini-USB plug and is typically found on newer devices such as smartphones and tablets. It is terminated on the other end with a Type A or Type B connector that plugs into a USB port on a computer or other device.
  • USB Type-C: This is the newest type of USB plug and is becoming increasingly ubiquitous. It is a rotationally symmetrical plug that can be inserted either way, making it easier to use. It also features a lot of pins and shielding, making it more robust and able to operate in harsh environments. It is terminated on the other end with a Type A or Type B connector that plugs into a USB port on a computer or other device.

USB Connector Features

USB connectors have several features that are designed to make them easier to use and more reliable. These include:

  • Polarization: USB plugs and connectors are nominally inserted in a specific orientation to avoid confusion and ensure that the correct lines are connected.
  • Molded relief: USB cables are often molded with a plastic overmolding that provides relief and potentially adds to the robustness of the cable.
  • Metal shell: USB connectors often have a metal shell that provides shielding and helps to keep the circuit intact.
  • Blue color: USB 3.0 connectors are often colored blue to designate their higher transfer speeds and compatibility with USB 2.0 devices.

Understanding USB Transfer Speeds

USB Generations and Speeds

USB has undergone multiple iterations since it first came out, and each version has its own transfer speed. The main USB ports found on modern laptops and devices are USB 2.0, USB 3.0, and USB 3.1. Here are the transfer rates for each generation:

  • USB 1.0: 1.5 megabits per second (Mbps)
  • USB 1.1: 12 Mbps
  • USB 2.0: 480 Mbps
  • USB 3.0: 5 gigabits per second (Gbps)
  • USB 3.1 Gen 1: 5 Gbps (formerly known as USB 3.0)
  • USB 3.1 Gen 2: 10 Gbps

It’s important to note that the transfer rates are limited by the slowest device connected to the USB port. So if you have a USB 3.0 device connected to a USB 2.0 port, the transfer rate will be limited to 480 Mbps.

USB Cables and Transfer Speeds

The type of USB cable you use can also affect transfer speeds. USB cables are defined by their ability to transmit data and power. Here are the common USB cables and their defined transfer speeds:

  • USB 1.0/1.1 cables: Can transmit data at up to 12 Mbps
  • USB 2.0 cables: Can transmit data at up to 480 Mbps
  • USB 3.x cables: Can transmit data at up to 10 Gbps

USB Superspeed and Superspeed+

USB 3.0 was the first version to introduce “Superspeed” transfer rates of 5 Gbps. Later versions of USB 3.0, known as USB 3.1 Gen 2, introduced “Superspeed+” transfer rates of 10 Gbps. This means that USB 3.1 Gen 2 doubles the transfer rate of USB 3.1 Gen 1.

USB 3.2, unveiled by the USB Implementers Forum in September 2017, identifies two transfer rates:

  • USB 3.2 Gen 1: 5 Gbps (formerly known as USB 3.0 and USB 3.1 Gen 1)
  • USB 3.2 Gen 2: 10 Gbps (formerly known as USB 3.1 Gen 2)

USB Power Delivery (PD) and Charging Speeds

USB also has a specification called USB Power Delivery (PD), which allows for faster charging speeds and power transfer. USB PD can deliver up to 100 watts of power, which is more than enough to charge a laptop. USB PD is prevalent in newer laptops and devices, and you can identify it by looking for the USB PD logo.

Identifying USB Transfer Speeds

Knowing the different USB transfer speeds can help you identify and diagnose potential problems with your devices. Here are some ways to identify USB transfer speeds:

  • Look for the USB logo on your device or cable. The logo will indicate the USB generation and speed.
  • Check your device’s specifications. The specifications should list the USB version and transfer speed.
  • Spend some time moving files between devices. This will give you an idea of the transfer speed you can expect.

Understanding USB transfer speeds can be complicated, but it’s important to comprehendible if you’re stuck naming the maxes of your devices. By taking advantage of the latest USB technologies, you can achieve higher transfer rates and gain higher efficiency.


USB Power Delivery (PD)

USB Power Delivery (PD) is a request-and-delivery technology based on certain USB connectors and cables that provides higher performance and charging capabilities. PD is a standard that allows for up to 100W of power delivery, which is enough to charge a laptop. PD is supported by certain Android devices and laptops, as well as by some USB charger brands.

USB Charging

USB charging is a feature that allows USB devices to be charged through a USB port. USB charging is supported by most USB devices, including smartphones, tablets, and cameras. USB charging can be done through a USB cable connected to a charger or a computer.

USB Tools and Test Labs

USB tools and test labs are resources that developers can use to test their USB products for compliance with the USB specification. The USB-IF provides a document library, product search, and contact information for USB compliance testing.

USB Proprietary Charging

USB proprietary charging is a variant of USB charging that has been developed by certain companies, such as Berg Electronics, a subsidiary of NCR, and Microsoft. This charging method uses a proprietary connector and charging protocol that is not endorsed by the USB-IF.

USB Licensing and Patents

The USB-IF owns patents related to USB technology and charges a licensing fee to manufacturers who want to use the USB logo and vendor ID. The USB-IF also licenses the PoweredUSB standard, which is a proprietary charging and data transfer standard developed by the USB-IF. USB compliance testing is required for PoweredUSB products.

USB Compliance and Press Releases

USB compliance testing is required for all USB products, including those that use proprietary charging methods. The USB-IF issues press releases and provides resources for members and implementers of the USB specification. The USB-IF also provides a logo and vendor ID for compliant USB products.

Understanding USB Version Compatibility

Why is USB version compatibility important?

When trying to utilize USB devices, it is important to consider the compatibility of the USB version of the device and the port it will be plugged into. If the USB version of the device and the port are not compatible, the device may not run or run at a lower speed than desired. This means that the device will not be able to perform to its fullest potential.

What are the different USB versions?

USB versions include USB 1.0, USB 2.0, USB 3.0, USB 3.1, and USB 3.2. The USB version is determined by the transfer rates, power output, and physical connectors.

What is the biggest issue with USB version compatibility?

The biggest issue with USB version compatibility is that the USB connectors have changed over time, albeit for good reasons. This means that even if a computer or host device supports a certain USB version, the physical port may not be the correct type to fit the plug of the device.

How can you make sure your USB devices are compatible?

To make sure your USB devices are compatible, you need to consider the following variables:

  • USB version of the device and the port
  • Type of USB connector (Type-A, Type-B, Type-C, etc.)
  • USB transfer rates
  • Power output of the USB port
  • Desired capabilities of the USB device
  • Highest capability of the USB port
  • Type of USB device (flash drive, hard drive, charging device, etc.)

You can use a compatibility chart to find out which USB versions and plugs are compatible with each other.

What does USB version compatibility mean for transfer speed?

USB version compatibility means that the transfer speed of the device will be limited to the lowest USB version of the two components. For example, if a USB 3.0 device is plugged into a USB 2.0 port, the transfer speed will be limited to the USB 2.0 transfer rates.

USB Devices

Introduction to USB Devices

USB devices are external peripherals designed to attach to a computer via USB connectors. They offer a quick and easy solution for expanding a computer’s functionality and power. USB devices come in various shapes and sizes, and their number keeps increasing every year. Nowadays, USB devices are an essential part of modern computing, and it’s hard to imagine a computer without them.

Examples of USB Devices

Here are some examples of USB devices:

  • USB disk: A small device that contains flash memory for storing data. It’s a modern alternative to the old floppy disk.
  • Joystick/Gamepad: A device used for playing games on a computer. It offers a lot of buttons and fast reaction times.
  • Headset: A device used for listening to audio and recording vocals. It’s a popular choice for podcasting or giving interviews.
  • iPod/MP3 Players: A device used for storing and playing music. It can fill up with thousands of songs and can be attached to a computer for syncing.
  • Keypad: A device used for inputting numbers and text. It’s a good alternative to a full-size keyboard.
  • Jump/Thumb Drive: A small device that contains flash memory for storing data. It’s a modern alternative to the old floppy disk.
  • Sound Card/Speakers: A device used for playing audio. It offers better sound quality than a computer’s built-in speakers.
  • Webcam: A device used for recording video and taking pictures. It’s a popular choice for video conferencing and streaming.
  • Printers: A device used for printing texts and images. It offers various ways of printing, such as inkjet, laser, or thermal.

USB OTG Devices

USB On-The-Go (OTG) is a feature that some USB devices offer. It allows a device to act as a host and communicate with other USB devices. Here are some examples of USB OTG devices:

  • Mobile phone: A device that offers USB OTG functionality. It can be used for attaching USB peripherals, such as a keyboard or a mouse.
  • Camera: A device that offers USB OTG functionality. It can be used for attaching a USB flash drive for storing pictures and videos.
  • Scanner: A device that offers USB OTG functionality. It can be used for converting scans of documents or images into digital files.

Locating USB Ports on Your Devices

Typical Locations of USB Ports

USB ports are like bulk cable interfaces that allow modern personal and consumer electronics to connect with each other. They can be found in a variety of locations on your devices, including:

  • Desktop computers: usually located on the back of the tower
  • Laptops: typically located on the sides or back of the device
  • Tablets and smartphones: additional USB ports may be located on charging blocks or stands

How USB Enumeration Works

When you connect a USB device to your computer, a process called enumeration assigns a unique address to the device and begins the process of identifying it. This is called being enumerated. The computer then finds out what type of device it is and assigns the appropriate driver to control it. For example, if you connect a mouse, the computer sends little commands to the device, asking it to send back information about its parameters. Once the computer has verified that the device is a mouse, it assigns the appropriate driver to control it.

USB Speeds and Bandwidth

USB 2.0 is the most common type of USB port, with a maximum speed of 480 Mbps. USB 3.0 and 3.1 are faster, with speeds up to 5 and 10 gigabits per second, respectively. However, the speed of a USB port is not guaranteed, as it is divided among all connected devices. The host computer controls the flow of data by dividing it into frames, with each new frame starting in a new time slot. This ensures that each device is given a fair amount of space to send and receive data.

Keeping Track of Your USB Devices

With lots of USB devices to choose from, it can be hard to keep track of which one is which. Many manufacturers clearly mark their devices with logos or labels, but if you have a lot of devices, it can still be difficult to determine which one is which. To help with this, you can use a USB manager to open a list of all installed USB devices and determine which one you want to use. Simply click on the device you want to use, and it will be assigned to the appropriate port.


So there you have it, everything you need to know about USB. It’s a protocol that allows you to connect and communicate with a wide range of devices, and it’s been around for almost 25 years.

It’s changed the way we connect and use computers and it’s here to stay. So don’t be afraid to dive in and get your feet wet! It’s not as scary as it sounds!

I'm Joost Nusselder, the founder of Neaera and a content marketer, dad, and love trying out new equipment with guitar at the heart of my passion, and together with my team, I've been creating in-depth blog articles since 2020 to help loyal readers with recording and guitar tips.

Check me out on Youtube where I try out all of this gear:

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