protected mode An operating mode of x86 chips that lets the PC access the largest possible amount of memory. In protected mode, different parts of memory are assigned to different programs. This way, memory is "protected" in the sense that only the assigned program can access it. The phrase is often used to describe device drivers that operate in this mode. Windows and OS/2 run primarily in protected mode, but can switch between the use of protected-mode and real-mode applications. See also: device driver, real mode