Apple Support Document: Powering a Peripheral Through USB


The USB ports on Apple computers provide 5 V (Volts) and 500 mA (Milliamps) to each port, regardless of whether the port is USB 1.1 or USB 2.0. This is in compliance with USB specifications. On some newer Intel-based Macs, such as the MacBook (13-inch, Late 2007), when a device requiring more than 5V and 500mA is connected, the port with that device connected to it becomes a high-powered port capable of offering up to 1100 mA at 5 V. That port will continue to operate as a high-powered port until the device is removed. 

Sunday, 4 April 2010