Which statement best describes a key characteristic of a multiprogramming operating system in which CPU time is shared among jobs?

Introduction / Context:
Multiprogramming is an operating system technique that keeps multiple jobs in memory and switches the CPU among them to improve utilization and responsiveness. It is foundational to time-sharing and modern multitasking, allowing many programs to appear to make progress even on a single processor core.

Given Data / Assumptions:

• A single CPU can switch rapidly among multiple ready processes.
• Context switching creates the illusion of simultaneous progress.
• True simultaneous instruction execution requires multiple CPUs or cores, which is not a requirement for multiprogramming.

Concept / Approach:
Multiprogramming emphasizes concurrency (interleaving) rather than parallelism. The scheduler selects which process runs next, using policies like round-robin, priority, or shortest job first. While multi-CPU systems can execute instructions in parallel, multiprogramming does not mandate multiple processors; it simply requires the OS to manage multiple runnable jobs and switch among them efficiently.

Step-by-Step Solution:

Verification / Alternative check:
Historical time-sharing systems (e.g., on mainframes and minicomputers) implemented multiprogramming well before symmetric multiprocessing was common. Modern desktops still rely on this concept even when multiple cores are present—each core also multiprograms among threads.

Why Other Options Are Wrong:

• (a) Simultaneous instruction execution on one CPU is not possible; it is time-sliced.
• (c) Multiple CPUs are not required for multiprogramming; they enable parallelism, not mere concurrency.
• (d) “All of the above” fails because (a) and (c) are not accurate requirements.
• (e) Not applicable because a correct statement exists in (b).

Common Pitfalls:
Confusing concurrency (interleaving) with parallelism (true simultaneity); assuming that “multi-” in multiprogramming implies multiple CPUs; neglecting the role of context switching and CPU scheduling policy.

Final Answer:
Concurrent processing of two or more programs by interleaving their execution on one CPU