A resident monitor is a piece of system software that was used in many early computers from the 1950s to 1970s. It can be considered a primitive precursor to the operating system. The name is derived from a program which is always in the computers memory thus being "resident".
On a general-use computer using punched card input, the resident monitor governed the machine before and after each job control card was executed, loaded and interpreted each control card, and acted as a job sequencer for batch processing operations. The functions that the resident monitor could perform were: clearing memory from the last used program (with the exception of itself), loading programs, searching for program data and maintaining standard IO routines in memory.