What is a system call and give examples?

A system call is the interface between a user program and the operating system kernel, allowing programs to request privileged operations. When invoked, CPU switches from user mode to kernel mode. Categories include: Process control (fork, exec, exit), File management (open, read, write, close), Device management (ioctl), Information (getpid, time), Communication (pipe, socket). System calls provide controlled access to hardware and protected operations.