Which of the following is an example of a real-time operating system?

A real-time operating system (RTOS) is built to process inputs and deliver outputs within a strict, deterministic time bound, or deadline, so that timing is guaranteed and not just fast on average. A general-purpose operating system instead optimizes for overall throughput and fair multitasking, where occasional delay is acceptable.

QNX is a microkernel-based RTOS engineered from the ground up for deterministic, low-latency task scheduling. This is why it is widely used in embedded, automotive, and industrial control systems, where missing a timing deadline can cause the system to fail.

• Windows 10: a general-purpose desktop operating system optimized for interactive multitasking, not for deterministic timing guarantees.

• UNIX: a general-purpose multi-user, multitasking operating system; standard UNIX does not provide the deterministic guarantees of a true RTOS (separate real-time UNIX variants exist but are not standard UNIX itself).

• Linux: a general-purpose operating system; although real-time patches or variants (such as PREEMPT_RT) exist, the standard/vanilla Linux kernel does not guarantee hard real-time deadlines.

Among the given options, only QNX is built as a true real-time operating system, so QNX is the correct answer.