Make sure you have an external USB (also called a thumb drive or flash drive) ready. If not, you’ll need to create a bootable Windows USB drive. If you have a Windows 10 or Windows 7 startup DVD, you can skip the next paragraph. Note that this process will delete the OS and all files, but it won’t permanently erase them.
That means your primary drive won’t be in use, so we’re able to work on it. To get around that, we’ll run Windows from an installation DVD or a USB drive. You can’t format the primary drive while it’s running, for the same reason that you can’t repair a car engine while driving. Your C drive (C:) is your primary drive where the operating system (OS) is located. How to format a primary drive (C:) on Windows But it’s a little different if you’re formatting the primary drive, a secondary internal drive, or an external hard drive. Formatting a hard drive on Windows is largely the same whether you’re using Windows 10 or 7.
