System Call

Problem

Applications need to read disks, create network connections and allocate resources. But letting every application directly control hardware would destroy isolation and security.

Solution — System Calls

Applications request privileged operations from the kernel.

Application
    ↓ read()
Kernel
    ↓
Disk

The kernel decides whether and how the operation may happen.

Core idea: system calls are the controlled boundary between applications and the operating-system kernel.