Apple computers and displays with USB 1.1 or USB 2 ports provide:
- Up to 500 mA (Milliamps) at 5 V (Volts) to most Apple USB peripherals and all USB peripherals not made by Apple in compliance with USB specifications.
Apple computers with USB 3 ports provide:
- Up to 900 mA (milliamps) at 5 V (Volts) to most Apple USB peripherals and all USB peripherals not made by Apple in compliance with USB specifications.
Note: Some USB peripheral devices not manufactured by Apple may have unique power requirements. These may exceed the power allotment on an individual USB port. Those devices may require you connect them to multiple USB ports or may have external power sources that must be present for them to function.
Apple peripheral devices may request more than 500 mA (Milliamps) at 5 V (Volts) from a port to function or to allow for faster charging. Such Apple peripheral devices include:
- Apple MacBook Air SuperDrive (when connected to supported computers)
- Aluminum Wired Keyboard*
To meet requests for additional power from these Apple peripherals and devices, some Apple computers and displays can provide up to 1100 mA at 5 V through the port to which the Apple peripheral or device is connected. This power is available under certain conditions:
- An Apple peripheral device must be plugged directly into an Apple computer or display. Apple peripheral devices connected to hubs will not have access to extra power above the standard USB specification of the port the device is connecting to (500 mA for USB 1.1 or 2, 900 mA for USB 3).
- Your Apple computer or display must be powered on and must be awake. If your Apple computer or display is asleep, all ports will provide their normal maximum output. If your Apple computer or display is powered off, no power will be provided.
- The port providing extra power is determined by the first Apple peripheral or device to connect to the Apple computer or display that requires power beyond 500 mA for USB 1.1 or 2, or 900 mA for USB 3. The remaining ports will continue to offer their normal maximum output. Some Apple computer and displays may offer the ability to operate more than one USB port at 1100 mA at 5 V. On those computers, the second or third port is enabled when an appropriate device is connected.
- An Apple computer started up to Windows via BootCamp will not provide extra power.
*When connected to a computer that supports a connection of 1100 mA at 5 V, the first port on the keyboard to have a device or peripheral connected to it that requests standard 500mA power will receive that power. At that point, 100 mA at 5 V is available through the remaining port on this keyboard. This keyboard does not support extra power out of its two ports simultaneously; it requests extra power from the host computer to provide power out of either one of its two ports, then the second keyboard port receives the standard 500mA.
Note: Apple computers and displays that were introduced before 2007 support only 500 mA at 5 V from their ports and do not offer additional power.
How many devices can I connect?
Multiple devices can receive high power simultaneously until the extra power is consumed. If further devices are connected requesting additional power, they will default to the maximum the port allows or the device will not function until the original device (or devices) using the extra power is removed.
If you have multiple supported devices that require additional power, an Apple LED Cinema display can supply additional power to a device connected directly to the display.
Confirming power usage in System Profiler
Open System Profiler to find more information about peripheral power requirements, or contact the manufacturer of your peripheral. For the most accurate information about power usage, make sure your device is connected directly to your Apple computer or display before opening System Profiler.
In the example above, the USB port is offering the default 500 mA to the port, as shown in the Current Available (mA) entry. The Current Required (mA) entry indicates the current the device needs to operate. In this example, Extra Operating Current (mA) indicates that this USB port is providing an additional 500 mA for use with this device.
If you have a peripheral (such as a hard drive, audio device, or camera) that is acting unexpectedly—such as not turning on or not being recognized by the computer—the peripheral may require more power than is available. If you have a USB peripheral or a chain of devices, such as a joystick plugged into a keyboard, which requires more than the available power try one of these options:
- Use a USB hub that comes with a power adapter.
- Check that the peripheral offers the ability to connect to more than one USB port at once.
- Find out if the peripheral comes with a power adapter.
- If you cannot confirm your device's use with a hub, connect the device directly to the Apple computer.