Formatting C means formatting the C drive, or the primary partition where Windows or your other operating system is installed. When you format C, you erase the operating system and other information on that drive.

Unfortunately, it’s not an easy process at all. You can’t format C drive like you can format any other drive in Windows, because you’re in Windows when you do it. Doing it from Windows would be like trying to lift a chair into the air while sitting on it — it just can’t be done.

The solution is to format C from outside of Windows, which means you need a way to do it from a location other than your Windows installation. The easiest method is to boot from an operating system (with formatting capabilities) via a CD/DVD/BD drive, flash drive, or floppy drive.

While that all sounds very complicated, it is actually very easy to do. Below are several completely free ways to format your C drive, all of which we have linked to extensive instructions.