The article explains that system calls are triggered by CPU‑provided privileged instructions (e.g., int 0x80, syscall, svc), with compilers translating high‑level calls into these instructions, and why user‑mode programs cannot access hardware directly for security reasons.
On modern operating systems, user‑mode programs are prevented from directly managing memory, executing privileged CPU instructions, or accessing hardware because such actions would break isolation, corrupt kernel data structures, and jeopardize system stability and security.
Attempting to bypass the operating system by directly managing memory, executing privileged CPU instructions, or performing raw hardware I/O from a user‑space application is prohibited; modern OS kernels enforce strict privilege levels, protecting critical data structures and ensuring system stability, and any such attempts are blocked or cause crashes.
Modern operating systems prevent user‑level programs from directly managing memory, executing privileged CPU instructions, or accessing hardware I/O, because such actions would break isolation, corrupt kernel data structures, and compromise system security, leading the OS to terminate the offending process.
