Different machines need different goals: a batch server wants the CPU busy, a laptop wants fast response, and an airbag controller wants a guaranteed deadline. OS types (batch, multiprogramming, time-sharing, real-time and others) are named by how they share the machine to meet that goal. Use the goal to classify a system in an MCQ. A common confusion is treating multiprogramming and multitasking as the same, or calling a phone OS real-time when it gives no hard deadline guarantee.