Microsoft says it plainly: wiping files off a PC may not remove them
Straight from Microsoft's documentation this month, describing what happens when you tell Windows to clear your files before reinstalling: "This option is faster, but files might be recoverable using specialized recovery tools."
The context is Cloud rebuild, a Windows 11 recovery feature currently in preview for Insiders. It reinstalls Windows by pulling the image and your drivers straight from Windows Update, with no USB stick and no dependence on the installed copy of Windows still working, which makes it useful on a machine that will not boot. When it reaches the point of clearing your data it offers two paths. "Remove files" reformats the system disk and is the quick one. "Remove & sanitize files" asks the drive's own hardware to securely erase itself before Windows goes back on, and Microsoft points you at it for a PC being recycled, returned or reassigned. With more than one drive in the machine, you choose between the Windows disk and all of them.
Microsoft is unusually frank about the limits. Windows asks the storage device to erase itself and reports back whatever the drive says, but, in Microsoft's words, it "cannot independently verify what the storage device did." If the erase fails, the screen offers to skip it and carry on regardless, and the documentation says not to take that offer if the machine is leaving your hands. The operation is irreversible, it can run for a long time on a large drive, and the PC must stay on mains power throughout. There is also a standalone DataSanitization.exe in the recovery environment for wiping a drive without reinstalling anything.
None of this has reached most people yet: Windows 11 only, preview only, and it needs a healthy recovery environment plus an internet connection. The principle travels anyway. Reformatting a drive is not the same as erasing what was on it, and "I reset it" is not the same as "it is gone." Whatever you do with an old PC, get your files off it first, which is what Tendvane's one-click backup of Documents, Pictures and Desktop is there for.