A USB hub splits one USB port into multiple ports using a chipset that manages data routing and power distribution between your computer and connected devices.
- You use a bus-powered hub for low-power devices like mice and keyboards
- You use a self-powered hub for high-draw devices like hard drives or printers
- Your hub and devices use compatible USB speeds (USB 3.x is backward compatible)
- A bus-powered hub is overloaded by high-power devices, causing disconnects
- Too many hubs are daisy-chained together
- Bandwidth-hungry devices share a single hub and slow each other down
The basics: upstream and downstream
Every USB hub has one upstream port that plugs into your computer and two or more downstream ports for your devices. The hub’s internal chipset acts as a traffic controller — it forwards data from the host to the right device and signals the host whenever a new device is plugged in so the computer can recognise and set it up.
USB 2.0 hubs broadcast host data to all downstream ports at once. USB 3.0 and later hubs route data point-to-point, which is more efficient and reduces interference between devices.
Bus-powered vs self-powered hubs
This is the most important distinction when choosing a hub.
- Bus-powered (unpowered): draws all power from your computer’s USB port. Limited to around 500 mA (USB 2.0) or 900 mA (USB 3.0) total. Fine for mice, keyboards, and flash drives.
- Self-powered: uses its own AC adapter for power. Can supply the full 500–900 mA per port, making it suitable for external hard drives, printers, and phone charging.
Plugging a power-hungry device into a bus-powered hub is the most common cause of random disconnections and data errors. If devices drop out unexpectedly, switching to a self-powered hub usually fixes it.
Bandwidth sharing
All devices on a hub share the upstream connection’s bandwidth. If you plug a USB 3.0 SSD and a webcam into the same USB 2.0 hub, both are capped at 480 Mbps total — split between them. For file transfers or video capture, use a USB 3.x hub and avoid mixing slow and fast devices on the same hub when speed matters.
Multi-TT (multi-transaction translator) hubs handle this better by giving each port its own transaction translator, allowing concurrent transfers rather than forcing devices to take turns. See the USB hub overview on Wikipedia for a deeper technical breakdown.
Common setups at a glance
| Setup | Works? | Need | Note |
|---|---|---|---|
| Mouse + keyboard on bus-powered hub | Yes | Any USB hub | Low power draw, no issues |
| External HDD on bus-powered hub | No | Self-powered hub | Insufficient power causes drops |
| USB 3.0 drive on USB 2.0 hub | Yes | — | Speed capped at USB 2.0 |
| Multiple SSDs transferring at once | Partial | USB 3.x multi-TT hub | Bandwidth shared without multi-TT |
If you’re also dealing with video output from a USB-C port, check out our guides on whether USB-C can connect to HDMI and why USB-C to HDMI stops working — the power and bandwidth principles are closely related.
Bottom line: USB hubs work by routing data and sharing power from a single host port across multiple devices. Choose a self-powered hub for anything that charges or spins, use USB 3.x for speed-sensitive devices, and avoid overloading bus-powered hubs to keep everything connected and stable.