external drive with 2 USB plugs

November 23, 2012 9:26 AM

I don't get it. If my external storage drive has two USB cables, do they both need to be plugged in? It seems to work with just one plugged in. Is it that one uses both when one wants extra speed?
posted by gnossie to Computers & Internet (10 answers total)

Nope, just one. Plugging in two doesn't make it any faster. Can't say for sure without looking at it, but it might just have an extra port on it so you can plug more drives in.
posted by empath at 9:27 AM on November 23, 2012

One uses both plugs when one's device needs more electricity than is provided by a single USB port. In the real world, that's almost never as far as I can tell.
posted by chudmonkey at 9:29 AM on November 23, 2012 [8 favorites]

If it works with one plugged in you're fine. You use the second one when a single USB port is not pumping out enough current to power the drive.
posted by griphus at 9:30 AM on November 23, 2012 [1 favorite]

The USB spec only required the host device to provide power output at 500mA. This was roundly exceeded by motherboard manufacturers. If your device needs more than 500mA a doubled headed cable may allow it to work on some hosts where it would otherwise fail. Sometimes it is possible to tell from the cabling which connector is power and which is power+data, but usually only one is wired for data.
posted by samworm at 9:54 AM on November 23, 2012 [1 favorite]

How would one be able to tell, specifically? (I assume they're not labeled "DATA+POWER" and "POWER" or something.)
posted by griphus at 9:58 AM on November 23, 2012

They are daisy-chained. The one closest to the drive is data + power usually.
posted by turkeyphant at 10:11 AM on November 23, 2012 [1 favorite]

One uses both plugs when one's device needs more electricity than is provided by a single USB port. In the real world, that's almost never as far as I can tell.

I've got an aging MacBook that sometimes needs both plugs to power a particular external drive, and I'm pretty sure I live in the real world.
posted by philip-random at 11:08 AM on November 23, 2012

Second vote for power requirements. Assuming your drive doesn't already have a second cable for power from the wall the second USB is for extra power. My personal experience is that laptops don't give enough juice for my drive but with desktops I'm ok just using one cable.

I've also got a drive that has two USB cables but where one actually ends in a pin at the hard drive end and is therefore very clearly power only.
posted by tiamat at 11:11 AM on November 23, 2012

The new Wii U requires you to use a hard drive in both USB ports for the power reasons mentioned above. If you use a hard drive at all.
posted by tacodave at 12:13 AM on November 24, 2012

Yeah, my enclosure has two cables, both of which are standard USB on the computer side, but which have different connectors ("power" and "data") on the drive side. Connecting the "data" cable without first connecting the "power" cable to my 4 year old laptop has the same results as if I simultaneously pulled both the laptop battery and power cord.
posted by anaelith at 12:18 AM on November 26, 2012