🧠 What is Multiprogramming?
Multiprogramming is an operating system technique where multiple programs are kept in memory at the same time, and the CPU switches between them to improve utilization.
The key idea:
While one program waits (e.g., for I/O), the CPU executes another.
⚙️ Why Do We Need Multiprogramming?
In early systems:
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Programs used to run one at a time.
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If one program had to wait for I/O (e.g., read a file), the CPU would sit idle.
Multiprogramming solves this by keeping multiple programs in memory so:
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CPU stays busy
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System throughput increases
📦 How It Works (High-Level Steps)
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Several programs are loaded into RAM.
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OS keeps track of each program’s state (running, waiting, etc.).
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CPU executes one, until it needs to wait (e.g., I/O).
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Then OS switches to another ready program.
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Cycle continues, ensuring no idle CPU time.
🖼️ Visual Analogy
Think of a chef (CPU) cooking for 4 customers (programs).
While one dish is baking (waiting for I/O), the chef starts chopping veggies for the next one.
No downtime. Everyone gets served faster.
🔁 Multiprogramming vs Multitasking vs Multiprocessing
| Feature | Multiprogramming | Multitasking | Multiprocessing |
|---|---|---|---|
| 🚀 Goal | Maximize CPU use | Make system responsive | Use multiple CPUs |
| 🧠 Mechanism | Switch between processes on I/O wait | Switch quickly between tasks | Run parallel tasks on multiple CPUs |
| ⚙️ Execution | Sequential, interleaved | Fast switching | Actual parallel execution |
| 🖥️ Hardware Needed | Single CPU is enough | Single CPU is enough | Requires multiple CPUs/cores |
🔐 Requirements for Multiprogramming
| Component | Purpose |
|---|---|
| 👨⚖️ CPU Scheduling | Decide which program runs next |
| 🧠 Memory Management | Keep multiple programs safely in memory |
| 📊 Job Scheduling | Choose which jobs to load into memory |
| 🛡️ Protection | Prevent one program from corrupting others |
| 📦 Context Switching | Save/restore process state during switches |
📈 Benefits
| Benefit | Why It Matters |
|---|---|
| 💯 Better CPU Utilization | CPU rarely idle |
| 🚀 Higher Throughput | More jobs completed per unit time |
| 🧠 Efficient Resource Use | Balances CPU and I/O tasks |
🧠 Interview-Ready Definition:
Multiprogramming is an operating system strategy where multiple programs are loaded into memory simultaneously, and the CPU switches between them to maximize utilization. It improves system throughput by ensuring the CPU stays busy while individual programs wait for I/O.