USB 2 Hub: What Actually Happens When You Split One Port
A USB 2.0 hub does not create bandwidth. It splits a single 480 Mbps channel across every connected device, and the shared channel is the reason a hub that works perfectly for a keyboard and mouse can make an external drive crawl.
Quick Answer
Use a USB 2.0 hub for low bandwidth, low power devices: keyboards, mice, printers, audio interfaces and dongles. Do not use one for external SSDs, capture cards or gigabit network adapters, which need USB 3.0. Choose a self powered hub whenever more than two devices draw more than 100 mA each.
Bandwidth Sharing
| Device | Typical sustained demand | Fine on a USB 2.0 hub |
|---|---|---|
| Keyboard and mouse | Under 1 Mbps | Yes |
| USB 2.0 webcam at 720p | 30 to 60 Mbps | Yes, one device only |
| Audio interface, 2 channels | 2 to 5 Mbps | Yes |
| Colour inkjet printer | Up to 100 Mbps burst | Yes, but slow with simultaneous use |
| External SSD | 400 Mbps and above | No |
| Gigabit network adapter | Up to 940 Mbps | No |
Power Budgets
Bus powered hubs
They borrow their power from the host port, which supplies 500 mA to the hub itself at minimum and 900 mA on newer ports. After the hub controller overhead, each downstream port usually gets 100 mA unless the hub reports a higher aggregate.
Self powered hubs
They include a power adapter and can deliver the full 500 mA per port to four or seven ports simultaneously. This is the only reliable way to run several bus powered devices together.
Physical Span and Cascading
The USB 2.0 specification allows five tiers of hubs between the host and a device. In practice, chaining more than two hubs behind a single host port introduces enumeration delays and intermittent dropouts, especially with devices that renegotiate power.
Real-World Applications
- Desk tidy up for keyboard, mouse and a wireless dongle: a four port bus powered hub is enough.
- Point of sale station with a scanner and receipt printer: self powered hub for current headroom.
- Rack mount server with USB licence dongles: powered industrial hub with screw mounts.
- Workshop bench with test instruments on USB serial: hub keeps a single host port free.
Choosing a Hub
- Count the devices and total their current draw.
- Pick USB 3.0 for any storage or network device.
- Choose self powered if three or more bus powered devices share the hub.
- Prefer a metal housing for installations that run warm.
- Check for over current protection, which prevents one faulty device from taking down the hub.
Related Guides
If you need SuperSpeed, read 2 port USB 3.0 hub. For extending a single port over distance instead of multiplying it, see USB cable extension. For high speed devices that should never share a hub channel, start with USB 3.0 A to B cable.
FAQ
Does a USB 2.0 hub slow down all connected devices?
All devices share one 480 Mbps channel. If a single device demands most of that, everything else on the hub slows accordingly.
Can I plug a USB 3.0 device into a USB 2.0 hub?
Yes, but it operates at USB 2.0 speed. A USB 3.0 SSD would fall from hundreds of megabytes per second to roughly 40 MB/s.
Why does my hub disconnect when I plug in a hard drive?
The drive exceeds the hub power budget. Use a self powered hub or a drive with its own power supply.
Are USB 2.0 hubs still worth buying?
Yes, for peripherals. They are inexpensive and entirely adequate for input devices, printers and USB serial adapters.