An external hard drive is a device you can use to save files like photos, movies, and videos. You can use an external hard drive as an external memory device for your computer or laptop, or if you want to safely store your files or transfer them to a different device. The 2.5-inch drives only use 1 cable for file transfer and power, which makes them suitable for on the go. A 2.5-inch hard drive needs a separate power cable and a socket, and work optimally with desktops.