When To Remove Usb While Installing Windows 10. Early on in the process Windows will copy all the files it needs from the USB drive to your hard drive. If there are any write operations in progress, Windows will make sure that everything is complete before ejecting the drive.
One of the first thing the update does is copy over the needed files from the installer location, whether it be a USB, DVD, local, or whatever you use.
In the Update & Settings window, on the left-side, click on Recovery.
Click the "I don't have a product key" option. Here, you can see all the partitions and drives from your PC, including external ones. Once you have a backup of your files, you can install Windows from a USB drive without any worries.