Apple's USB power famine

By Stephen Withers
Thursday, 01 May 2008 05:37

Opinion and Analysis

What's happening with USB power on the iMac?

Back on the iMac G5, each of the three USB ports could supply 500mA - plenty for any bus-powered device, and enough to allow the connection of an unpowered hub with multiple devices that only require the normal 100mA or less.

Fast forward to the "April 2008" iMacs, and things have changed. There are still three USB ports, but only one of them can be used as a high-power port at any given time (source: iMac Developer Note, Apple).

So if you upgrade to the new model, you may find that your old set of peripherals may not work correctly without the addition of a powered hub. This is especially likely to affect devices such as bus-powered hard drives (including iPods) and cameras, or configurations with multiple low-power devices connected via an unpowered hub.