What is USB?
USB is an industry standard for connecting computers and other devices. Many Mac computers have USB-A ports (sometimes referred to as USB 3 ports), which look like this:
USB 3.0 and USB 3.1 Gen 1 can transfer data up to 5 Gbps, and USB 3.1 Gen 2 can transfer data up to 10 Gbps.
What is USB-C?
USB-C describes the shape and style of a port on your computer and the connectors that you can plug into the port. USB-C ports look like this:
Several different data transfer standards, like USB 3 and Thunderbolt 3, can flow through a USB-C port and connector. You can also connect your computer's AC power adapter to a USB-C port with a compatible USB-C charging cable.
USB-C ports are reversible, so you don't have to worry about which side of the connector is up when you plug it in.
These Mac computers have Thunderbolt 3 (USB-C) ports that support USB 3.1 Gen 2 and Thunderbolt 3:
- iMac (Retina 5K, 27-inch, 2017)
- iMac (Retina 4K, 21.5-inch, 2017)
- iMac (21.5-inch, 2017)
- MacBook Pro (2016 and later)
These Mac notebooks have USB-C ports that support USB 3.1 Gen 1:
- MacBook (2015 and later)
You can use your USB 3 devices with the above Mac models using an appropriate adapter.
What version of USB does my Mac support?
You can use System Information or System Profiler to see what type of USB ports your Mac has, how fast these ports are, and what's currently connected to them. Learn more about identifying USB ports on your Mac.
What transfer rates does USB offer?
USB 3.1 Gen 2 can transfer data up to 10 Gbps. Newer Mac models with Thunderbolt 3 (USB-C) ports support these speeds.
Speeds of previous USB versions:
- USB 3 and USB 3.1 Gen 1 can transfer data up to 5 Gbps.
- USB 2 can transfer data up to 480 Mbps.
- USB 1.1 can transfer data up to 12 Mbps.
Does USB 3 offer more power than USB 2?
USB 3 devices can use up to 900mA of power (compared to 500mA used by USB 2 devices). You'll need to use a USB 3 cable to use the 900mA of power available. USB 2 cables don't support 900mA.
Why don't I see blue inserts on the USB ports of my Mac?
Some manufacturers use a blue insert to designate a USB 3 port or device. All USB ports on Mac computers that support USB 3 are USB 3 capable and don't have blue inserts.
What USB 3 devices are supported?
All devices that conform to what is commonly referred to as the "2008 version 1 USB 3.0 specification" are supported.
Are USB 3 hubs supported?
Hubs that conform to what is commonly referred to as the "2008 version 1 USB 3.0 specification" are supported.
How do I get the best performance from the USB 3 ports?
The first device you plug in will configure the port, so always connect USB 3-capable hubs or devices first.
What happens if I plug in a USB 2 device into the USB 3 port first?
If you plug in a USB 2 hub first, all devices connected or "daisy-chained" to that hub will operate up to the maximum transfer rate of USB 2 speed (480 Mbps).
What happens if I plug my USB 3 device into a USB 2 port?
Your device should be backwards-compatible with USB 2 ports. However, you won't get USB 3 speed and power may be limited to 500mA.
Is USB 3 supported in Windows 7 and 8 using Boot Camp?
Yes. USB 3 is supported natively in Windows 8. See Boot Camp: Frequently asked questions about installing Windows 8 for more information.
To implement USB 3 support on Windows 7 using Boot Camp, download and install the Windows Support Software (drivers). See Boot Camp: Installing Windows 7 Frequently Asked Questions for more information.
Are there differences between USB 3 cables and other USB cables?
Yes. USB 3 cables:
- Use more wires than other USB cables. This makes USB 3 cables a bit thicker than other USB cables.
- Usually have a blue insert.
- Have an "SS" symbol on the connector that plugs into the computer.
- Use a different connector on the device end than USB 2 cables.
- Can deliver more power to an attached device (900mA).
Can I use a USB 2 cable to connect a USB 3 device to my computer?
If the device end of the cable fits into the connector on the device, yes. However, because it has fewer wires, you won't get USB 3 speed and power may be limited to 500 mA.
How can I determine if my device is connected as a USB 3 device?
Use the System Information utility:
- From the Apple () menu, choose About This Mac.
- Click System Report.
- Under the Hardware heading on the left side of the System Information window, click USB.
USB 3 devices appear under USB 3.0 Bus, and USB 2 devices appear under USB 2.0 Bus. Click the device names to learn more about each one.
Why do my USB 3 devices seem to only work at USB 2 speed when I use virtualization software on my Mac?
Some virtualization software doesn't yet support USB 3. Contact the manufacturer of your virtualization software for more information.
Why don't some USB 3 devices activate or appear on the USB 3 bus?
Try these tips if a USB 3 device doesn't activate or appear on the USB 3 bus:
- Be sure you've installed the latest software updates available for your computer. To check, choose App Store from the Apple menu and see if any updates are available.
- Sometimes unplugging and plugging the device back in can resolve the issue.
- Try plugging the device into another USB port on the computer.
- Check to see if a firmware update is available for your device from the manufacturer.
- If the device came with an AC adapter, use it.
- Restart your computer.
- Try a different USB 3 cable.
- Try a different USB 3 hub.
Why do I have difficulty with Wi-Fi or Bluetooth devices when USB 3 devices are attached to my computer?
Some USB 3 devices can generate radio frequency interference that can cause Wi-Fi and Bluetooth devices operating in the 2.4GHz band to have issues communicating with your computer. Here are some tips to avoid this issue:
- If your USB device has a cable long enough that you can move the device, place it away from your Mac—and make sure not to place it behind your Mac, or near the hinge of its display. The antennas for Wi-Fi and Bluetooth are located there, and USB 3 devices placed there might interfere with your wireless connections.
- If you're using adapters or dongles on a Mac computer with Thunderbolt 3 (USB-C) ports, plug them into the front port on the left side of your Mac, or into the ports on the right side (if your computer has them). These ports are the farthest away from the antennas, making interference less likely.
- To avoid interference on the 2.4GHz band using Wi-Fi, try using the 5GHz band instead. You can change this on your wireless base station. Bluetooth always uses 2.4GHz, so this alternative isn't available for Bluetooth.