Resident monitor
A resident monitor was a piece of system software in many early computers from the 1950s to 1970s. It can be considered a primitive precursor to the operating system.
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.
Similar very primitive system software layers were typically in use in the early days of the later minicomputers and microcomputers before they gained the power to support full operating systems.
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