The trouble is that the presence of such zones very often makes it absolutely impossible not only to restore the OS, but even its final installation with the formatting of the media. Such zones in the environment of professional 'computer specialists' are called 'Bad sector' or 'Bad block' (from the English word Bad, that is bad). The cause is damage to hard disk sectors. Even a backup copy of the system does not always save. The thing is that such an unfortunate outcome is greatly contributed by the incredible density of recording on modern hard drives, as well as the complexity of modern SATA interfaces.
Oddly enough, sometimes the 'fall' of the operating system does occur without user intervention.
