<operating system, programming> The mechanism used by an application program to request service from the operating system. System calls often use a special machine code instruction which causes the processor to change mode (e.g. to "supervisor mode" or "protected mode"). This allows the OS to perform restricted actions such as accessing hardware devices or the memory management unit.
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Nearby terms: system analysis « system analyst « system board « system call » system catalog » System Control Language » Systeme International