Reference monitor
In operating systems architecture, a reference monitor is a tamperproof, always-invoked, and small-enough-to-be-fully-tested-and-analyzed module that controls all software access to data objects or devices (verifiable). The reference monitor verifies the nature of the request against a table of allowable access types for each process on the system. For example, Windows 3.x and 9.x operating systems were not built with a reference monitor, whereas the Windows NT line, which also includes Windows 2000 and Windows XP, was designed with an entirely different architecture and does contain a reference monitor.
The Reference Monitor concept was introduced in the Computer Security Technology Planning Study (Oct, 1972) by James Anderson & Co.
Systems evaluated at B2 and above by the TCSEC must enforce the reference monitor concept.