WD Elements 640 GB USB 2.0 Portable External Hard Drive Easy to Use - Just plug it in and it's ready to receive your data. USB Powered - These drives require no power adapter--they are powered directly through the USB cable.* Compact Design - Weighing in at only a few ounces, these tiny drives fit easily into pocket or purse. Designed to protect your data and put through a comprehensive battery of tests before they are ready for market