What is the primary purpose of a system call in an operating system ?

A system call serves as the fundamental interface between a user application and the operating system kernel. Its primary purpose is to allow programs to request access to protected system resources, such as files, memory, or network connections, in a controlled and secure manner. This mechanism ensures that user code cannot directly manipulate hardware or access critical data without permission, maintaining system stability and security. Option A is incorrect because user code runs in a restricted mode (user space) and cannot have full system access without transitioning to kernel mode via a system call. Option C is wrong because direct hardware communication bypasses the OS, which violates security and stability principles; the OS must mediate all hardware interactions. Option D describes process management functions, which are tasks performed by the OS itself rather than the specific purpose of a system call interface. Therefore, Option B accurately defines the core function of system calls as controlled resource requests.