For example:

Once the installation is complete and you have reached the new desktop screen, shut down your PC and plug your secondary internal and external drives back in. When you boot back up, Windows will automatically assign drive letters to them, and your data will be right where you left it. What Happens to Games and Apps on Secondary Drives?

For Windows users, this means that when you boot from installation media and reach the "Custom install" screen, you have full control over which drive and which partitions get modified. The installer presents a list of all connected drives and their existing partitions. You then select which partitions to delete or format on the drive where Windows will be installed. Other drives—even other partitions on the same physical disk that are separate from your system drive—remain untouched as long as you do not intentionally delete or format them.

When you perform a clean install using a USB boot drive, you eventually reach a screen asking,

This is a built-in software feature. Depending on your manufacturer or OS settings, a factory reset might give you an explicit choice to wipe "all drives" or "only the drive where Windows is installed."

The partition you select will be wiped (or data moved to a Windows.old folder if you don't format) to make room for the new OS.

For users with multiple physical drives, several best practices can ensure that your data remains safe during a clean installation.

Back up all important files from your system partition, including user directories, to external storage or cloud services before beginning the process. Note that while you can back up your personal files, programs cannot be backed up in a way that preserves their functionality—they must be reinstalled after the clean installation.

If you want, tell me which OS installer you're using (Windows, macOS, Ubuntu, etc.) and whether you have multiple drives; I’ll give step-by-step instructions for a safe clean install in that environment.

The safest method for desktop PCs is to power down the computer and unplug the SATA or NVMe cables from your secondary internal storage drives. Leave only the target boot drive connected. If the installer cannot see the drives, it cannot wipe them. Reconnect them after the installation finishes. 2. Unplug External Storage

Sometimes, users realize their files were only on the desktop (C: drive), which is wiped. Even if the secondary drives are safe, your primary user profile data is gone. How to Ensure "Exclusive" Wiping