Windows 10 was originally launched in 2014, however was only available as Technical Preview. Since Microsoft changed a lot of things in the new Windows OS, they wanted to test it thoroughly before going for final release.
External storage has become a very common phenomenon. A lot of people are now opting for external storage devices like portable hard drives or USBs to store data instead of internal drives. It is because of its mobility as people can just take their external storage device with them anywhere they want to.