System Calls and How Software Interacts with Hardware
System Calls and How Software Interacts with Hardware System calls are the bridge between most software and the computer’s hardware. They let programs ask the operating system to perform tasks that require privileged access, such as opening a file, sending data over the network, or talking to a printer. Without system calls, software would be limited by what a user process can safely do. Inside the operating system, a protected boundary separates user space from kernel space. A program uses a system call to enter kernel mode, where the OS checks permissions, switches the CPU to a higher privilege level, and schedules work. This switch keeps programs safe and the system responsive. ...