What is the difference between multiprogramming, multitasking, and multiprocessing?

These terms describe different aspects of concurrent execution: Multiprogramming: multiple programs are kept in memory simultaneously. When one process waits for I/O, the CPU switches to another instead of idling. Goal: maximize CPU utilization. CPU runs ONE program at a time, but multiple programs are loaded. Single-CPU system. Without: CPU → Run P1 → Wait I/O (idle) → Run P1 → ... With: CPU → Run P1 → Wait I/O → Run P2 → Wait I/O → Run P3 → ... Higher CPU utilization!. Multitasking (time-sharing): extension of multiprogramming where the OS rapidly switches among multiple jobs — giving each a small time slice (quantum). Users feel all programs are running simultaneously. Interactive response time is important. Same single CPU — context switching creates the illusion of parallelism. Focus: responsiveness, user experience. Multiprocessing: system has MULTIPLE physical CPUs (or cores). Processes genuinely run simultaneously on different CPUs — true parallelism. Types: Symmetric Multiprocessing (SMP — all CPUs equal, share memory, run OS and user processes); Asymmetric (one master CPU runs OS, others run user processes); NUMA (Non-Uniform Memory Access — CPUs have local fast memory and slower remote memory). Summary: multiprogramming = multiple programs in memory (CPU efficiency); multitasking = rapid switching between programs (responsiveness); multiprocessing = multiple physical CPUs (true parallelism). Modern systems have all three: multiple CPUs, each rapidly switching among many programs all loaded in memory.