Checking how much power a USB device requires

I have a number of USB-attached hard disks that I use for portable mass storage, backups, etc. Very occasionally, Windows XP will report that there has been a power surge on the USB port and that it has been shut down. This can happen when the total number of devices attached to a USB hub (internal or external) exceeds the total power available. I’ve always treated that as a minor annoyance (and as these disks have two USB connections and a Y-shaped cable, I can simply use two ports) but then a few days back I noticed something I’ve never see before – the ability to view power details for (or more precisely current drawn through) a USB root hub:

USB device power draw

As can be seen in the example above, my scanner is using the full 500mA on its port, but there is still a port available which could potentially provide another 500mA. To view this information, open Device Manager from the Computer Management MMC snap-in and expand the Universal Serial Bus Controllers node. There will normally be a number of controllers listed, along with some devices and USB root hubs. Each USB root hub should have include power details within its properties.

Checking my IEEE 1394 (FireWire/i.Link) controller doesn’t seem to offer the same facilities, presumably because it doesn’t have the same concept of a root hub.

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