operating systems

Most candidates say 'rings' and stop. The interviewer is listening for who enforces the boundary, where the kernel must distrust its caller, and why one kernel bug undoes every process boundary at once.

Isolation is enforced by page tables and credentials, then deliberately punched through by debuggers, shared memory and IPC. A strong answer names both the wall and the doors.

The definition takes one sentence. The interview is about the four ways privilege actually moves, and why most escalations are misconfigurations rather than exploits.

Typing a command sets off a chain: a system call, a permission check, a loader, dynamic linking and memory protections. Every step is a place security is enforced, and a place it can be bypassed.