Universal Serial Bus, or USB for short provides a single, standardized, easy to use way to connect devices to a computer. It uses a much higher data transfer rate than many common serial data formats. You can attach up to 127 individual devices to your computer using USB. USB can also supply enough power to smaller USB devices taking away the need to plug them into an external power source. This makes USB the primary connection for mobile workstations and smartphones.
Beyond its convenience, USB has evolved over time to support faster speeds and a wider range of uses. Early versions of USB were designed mainly for basic peripherals, but newer standards allow for high‑speed data transfers capable of handling large files, high‑resolution video, and advanced external storage devices. This evolution has made USB a reliable choice not just for simple input devices, but also for demanding tasks such as backups, multimedia editing, and device synchronization across multiple platforms.
Some common examples of USB devices include:
- Printers
- Scanners
- Mice
- Keyboards
- Joysticks
- Digital cameras
- Webcams
- Speakers
- External hard drives
If the device you are installing is new to the computer, Windows will auto detect it and automatically installs the necessary drivers via Windows Update. If the device has already been installed, the computer will start using the device right away. USB devices can be connected and disconnected at any time making them hot swappable.
Modern USB Connectors
While the classic rectangular Type-A port is still common on PCs, the industry has shifted to USB-C as the universal standard.
- USB-C: A small, reversible connector that supports high-speed data, video output (DisplayPort), and high-wattage power delivery.
- USB-A: The traditional port used for mice, keyboards, and older flash drives.
- Micro-USB: A legacy connector still found on older cameras and budget electronics.
Typical USB C cable
The PC host typically has connections for two or more external USB ports. Each of these connectors on the PC is actually a connection to a separate root hub inside the PC. A USB host controller in the PC is integrated into the chipset on newer systems and orchestrates the sending and receiving of data between the PC and an external device. When the host powers up, it queries all of the devices connected to the bus and assigns each one an address. The host keeps track of the total bandwidth that all of the isochronous and interrupt devices are requesting.
If you don’t have enough USB ports on your computer to accommodate all of your devices then you can buy a USB hub. Hubs can be powered or unpowered. Hubs can be part of the device such as a keyboard or monitor with USB connections on it. Modern USB-C hubs often feature Pass-Through Charging, allowing you to charge your laptop using the same hub that connects your peripherals. The USB standard allows for devices to draw their power from their USB connection. A high power device like a printer will have its own power supply, but low power devices like mice and cameras can get their power from USB bus so you don’t need external power. Passive USB 3.0 cables are typically limited to 3 meters to maintain speed, while high-quality USB-C cables vary depending on their Power Delivery (PD) rating.
USB Performance Standards
USB naming conventions can be confusing. Here is a breakdown of the speeds you will encounter today:
- USB 2.0 (High Speed): 480 Mbps — Standard for mice and keyboards.
- USB 3.2 Gen 1 (SuperSpeed): 5 Gbps — Common for external hard drives.
- USB 3.2 Gen 2×2: 20 Gbps — High-end external SSDs.
- USB4 / USB4 v2: 40 to 80 Gbps — The latest standard, primarily using the USB-C connector for massive data throughput.
Many USB devices can be put to sleep by the host computer when the computer enters a power saving mode. There is a set of drivers included in the newer versions of Windows that support certain devices called human interface devices or HIDs. These devices don’t require much data to be transferred to or from the host computer. The firmware inside these peripheral devices must support the Windows HID protocol if you want to use the existing HID drivers.
USB Support in Windows 10 & 11
Modern Windows operating systems include a “USB Stack” that supports almost all devices natively. If a device isn’t recognized, it is usually due to a physical port failure or an “Unknown USB Device” error in Device Manager, which can often be fixed by uninstalling the Root Hub and restarting the computer.
Here is an updated article about USB cables and connectors.
