Certified Information Systems Security Professional (CISSP) Practice Exam

What is the function of a system call in an operating system?

1. To initiate hardware diagnostics

2. To allow processes to communicate with the kernel

3. To manage user file permissions

4. To encrypt sensitive information

The correct answer is: To allow processes to communicate with the kernel

The function of a system call in an operating system is fundamentally to enable processes to communicate with the kernel. The kernel is the core component of an operating system that manages interactions between hardware and software. Since user applications typically run in user mode with restricted access to hardware resources, system calls serve as an interface that allows these applications to request services and access hardware resources securely. When a process requires services provided by the kernel—such as reading from a disk, creating a new process, or allocating memory—it makes a system call. This call effectively transitions the process from user mode to kernel mode, allowing it to execute the requested operation safely and efficiently. This mechanism is essential for resource management, security, and maintaining system stability. While other functions such as managing user file permissions and encrypting sensitive information are vital roles within an operating system, they do not encapsulate the primary purpose of a system call. This functionality specifically focuses on the interaction between user applications and the system kernel.