System vs Procedure Call

Understanding the distinction between system calls and procedure calls

This easy question tests your grasp of a fundamental operating-systems concept: the boundary between user-space and kernel-space execution, and how control flows differently depending on whether you're invoking a procedure or making a system call.

The question asks you to identify which statement about these two mechanisms is incorrect. To answer it well, you need to understand the key differences in how they operate—including privilege levels, context switching, performance implications, and the role of traps or interrupts. Many candidates conflate properties of one with the other, or misremember the exact semantics of how the CPU transitions between modes.

• User-space vs. kernel-space execution context
• Privilege levels and mode switching
• Cost and overhead differences
• Control transfer mechanisms (call/return vs. trap/return)