Files sizes are getting bigger and bigger, and we have more and more that we need to carry around. A portable hard disk is a great way to transfer files from one computer to another. Powered through your computer's USB port, you can carry these small and cheap portable hard disks anywhere. They make a great accessory for your laptop since many laptops have limited storage space. The best portable hard disks can transfer files at high speeds through USB 3.0 compatible ports. You can even use them to backup your entire computer hard drive for extra security.