I’m in the market for a usb-powered external hard drive. Several of the reviews I’ve read warn the buyer to check to see that their USB port provides enough power. The drive I’m looking at requires 1000 milliamps and some USB ports only deliver 500.
That’s all well and good, but when I go into the USB root hub properties, there is no power tab. WTF? I’m running XP on a year-old HP laptop with all the updates. Any ideas?
You should lookup your laptop model number on the manufactures web site and see if you can find the information there.
The USB spec calls out a maximum of 500mA per USB port. There might have been amendments to the standard that I am unaware of. But a quick web search still shows 500mA as the maximum.
I just checked and my machine (high spec, about a week old) only offers 500mA through the USB but I bet if I plugged a 1Amp device it would work 
I can’t see why a manufacturer would put a 0.5A regulator in, just for it to melt when somebody uses a slightly over-power device.
As for why your tab is no longer appearing, have you tried uninstalling the device in Device Manager, rebooting and checking whether it reappears? Right click the USB device, Uninstall… and (hopefully) voila!
tim
Some USB devices use two adjacent ports to acquire the 1000mA. Others have their own power supply.
Trying to draw 1000mA from a 500mA supply would not be a good idea.
I ended up getting a 160GB Maxtor Mini, which has a Y-cable with two USB plugs. The Western Digital I was originally looking at came with just a single USB cable.
I checked the HP laptops at the store, they had power tabs that indicated 500 mAh, as you have said. I just thought it was very peculiar that those tabs are missing on my system.
Thanks for your replies!
It would be a pretty piss poor out of USB spec computer that was damaged by a USB device drawing too much power. The device probably won’t work but the laptop should not be damaged. The USB spec calls for over current protection on the data and power pins.
I finally found these power tabs you are talking about. On my machine they all say 500mA.
I also am unaware of an increase in the standard 500mA USB supply.
My friend and I once mis-wired a component in a USB device we were building, resulting in a large power draw. In Linux, the USB port being used was turned on and off rapidly. In Windows, an informative message box appeared indicating the excessive draw, and the USB port was disabled until next reboot.