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I don't know about one that is powered through the USB cable, but if you want a great hard drive with a USB connection and an external power supply, I would recommend Other World Computing. Their best drives have multiple connections, so you would probably want to look under the Firewire section in addition to the USB section. They have some great ones that are USB/Firewire/eSATA.
 
You will need a 2.5" drive to have it be powered over USB. A Western Digital My Passport for instance.
 
oh i see. i have al macbook. no firewire.. 2.5 dont come in high capacity:(
thanx for the help

You can still get a 3.5" high-capacity hard drive with a USB connection and an external power supply. Also, if I am reading this one correctly, it is USB-powered (and very high-capacity.)
 
The ministack uses an external power supply

At the top of the webpage, it says, "Adds Hard Drive space + Powered FW/USB Hubs" and at the bottom, it says, "Plus, with its powered FireWire and USB hubs, you can connect multiple desktop devices including scanners, printers, memory card readers, digital cameras, and iPods® – all at once!"

Even if it does use an external power supply, I think that the OP is actually looking for a hard drive with a USB connection, not USB power. The OWC drives like the MiniStack would qualify.
 
At the top of the webpage, it says, "Adds Hard Drive space + Powered FW/USB Hubs" and at the bottom, it says, "Plus, with its powered FireWire and USB hubs, you can connect multiple desktop devices including scanners, printers, memory card readers, digital cameras, and iPods® – all at once!"

Even if it does use an external power supply, I think that the OP is actually looking for a hard drive with a USB connection, not USB power. The OWC drives like the MiniStack would qualify.

And at the bottom of the page, if you click the image it shows a DC in port. It's externally powered. The fact that it provides powered FW/USB hubs suggests that it needs to power these ports itself (ie via external power source) since there is no possible way to draw enough power from a computer's USB port to power the drive and the hubs.

The OP states in their first post that they want a USB powered HDD only.

To the OP: If you're looking for a USB powered drive, unfortunately they do not exist in a high enough capacity yet. 500GB is the highest you can go. How much storage space are you looking for?
 
"title says it all. im looking for an external hdd usb powered only. do they exist and if so where to find"

DON'T rely on an external drive that has "USB port power only". By that I mean the drive is designed to run using USB bus power, and has no provision for connecting an external power supply (usually a power supply block).

The reason you don't want a drive like this for use with the Mac, is that most Macs supply a LOWER LEVEL of USB power to the USB bus, than do PC's. I'm not sure why Apple chose to do this, but it definitely can be a problem when trying to get a USB drive up and running on the Mac using only USB power.

This will become even more problematic depending on if you have any other USB devices hooked up to your bus, as well. Each device will consume a little power, and if you try to plug in a power-hungry device like an external drive, you may either get a warning that there isn't enough power to connect the device, or, you may connect the drive, hear it spin a little, but it will never "mount up" on the desktop.

Having said that, there may in fact be a few external USB enclosures that are "power-miserly" enough to permit mounting on the Mac. The problem is finding the right one that you know will mount all the time and not give problems.

There is another work-around that may work sometimes. This involves a "dual-headed" USB cable shaped like a "Y". The "single end" goes to the USB powered drive, and the double-headed end goes to TWO USB ports on the Mac. This is because one port alone can't provide enough power, but using two ports might.

If you want a USB external drive that you KNOW will mount all the time, every time, get one that has an external power supply. That's the only way to be sure.

If you have a firewire port on the Mac in question, a firewire drive is the better solution. The Mac's firewire bus DOES provide enough power to mount firewire drives.
 
I have two WD Elements 750GB (They also have 1TB versions) drives that are USB 2.0-only powered. I found the older ones cable doesn't work so well and doesn't always like to mount. Because I have two I just use the other cable although I can no longer mount both of them at the same time with any consistency. Both are under the 1yr warranty period and I'll probably get the cables replaced soon. Other than the cable issue the drives have worked beautifully, and I think the 1TB ones are less than $100 on amazon now.
 
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