Every time you open a file, access the internet, allocate memory, or create a new process, something important happens behind the scenes. Your application does not directly control the hardware. It asks the operating system to do it. That request is called a system call . System calls are the controlled communication bridge between user applications and the operating system kernel. Understanding them is key to understanding how an OS really works. Why Applications Cannot Access Hardware Directly Applications run in a restricted environment. They cannot: Access physical memory directly Control the CPU scheduler Communicate with hardware devices Modify kernel memory Execute privileged instructions Related: User Mode vs Kernel Mode This restriction exists for security and stability. If every application could directly access hardware, the system would become: Unstable Vulnerable to attacks Prone to crashes The operating system protects itself by forcing applications to request services s...
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