The operating system's file system knows where the data are physically stored (which sectors), and interaction between the app and operating system is through the programming interface (API).

Fortunately, Windows 2000, XP, and Server 2003 use a mechanism called Windows File Protection (WFP) to prevent critical system files from being overwritten.

Logical file protection is provided by the operating system, which can designate files as read only. This allows both regular (read/write) and read only files to be stored on the same disk volume.

How to run sfc /scannow command? System File Checker or sfc.exe scans for, restores corrupt Windows system files protected by Windows File Protection (WFP).

Some software you may know and lean on won't work in El Capitan due to a new security feature that locks down system files and directories. Here's how to modify that.