🧩 Introduction to Multiprocessor Operating System
A Multiprocessor Operating System (MPOS) is designed to manage two or more CPUs within a single computer system. These CPUs share memory and I/O devices and work together to improve performance, reliability, and throughput.
✅ Key Goals:
- Efficient parallel processing
- Load balancing across CPUs
- Resource sharing without conflicts
- Faster execution of processes
🏛️ Architecture of Multiprocessor Systems
Multiprocessor systems are broadly categorized into the following:
1. Tightly Coupled Systems
- Processors share single memory and are closely connected.
- Common bus or crossbar used for inter-CPU communication.
- Low communication latency.
2. Loosely Coupled Systems
- Each processor has its own memory.
- Communication via message passing.
- More like distributed systems, but in a single chassis.
🔄 Types of Multiprocessor Architectures
| Architecture Type | Description |
|---|---|
| SMP (Symmetric Multiprocessing) | All CPUs share a single OS and memory; equally capable. |
| ASMP (Asymmetric Multiprocessing) | One master CPU controls others (slaves). |
| NUMA (Non-Uniform Memory Access) | CPUs have local memory but can access others’ memory more slowly. |
| Clustered Systems | Several systems connected to work as one. Closer to distributed systems. |
🏗️ Structure of Multiprocessor Operating System
A multiprocessor OS has the following components:
1. Kernel
- Single or replicated kernel depending on system design.
- Manages hardware, processes, memory, and I/O devices.
2. Processor Management
- Tracks which CPU runs which process.
- Handles CPU allocation and load balancing.
3. Memory Management
- Ensures safe sharing of memory among multiple CPUs.
- May use cache coherence protocols (MESI, MOESI).
4. Process Synchronization
- Manages concurrent access to shared resources using semaphores, mutexes, and monitors.
🔁 Synchronization in Multiprocessor OS
Synchronization is crucial to prevent race conditions and inconsistent data when multiple CPUs access shared memory.
🧩 Techniques Used:
| Technique | Description |
|---|---|
| Locks (Mutex) | Allows only one thread to access critical section. |
| Semaphores | Signal-based mechanism for managing access to resources. |
| Spinlocks | Busy-waiting lock used in SMP systems for short waits. |
| Barriers | Force threads to wait until all have reached the same point. |
| Atomic Operations | Operations like test-and-set, compare-and-swap ensure synchronization at hardware level. |
🔧 Example Use Case:
If two CPUs try to update the same variable, a mutex lock ensures that only one can do so at a time.
🧮 Scheduling in Multiprocessor OS
Scheduling in MPOS deals with deciding which CPU runs which process and when.
🔁 Types of Scheduling:
1. Asymmetric Scheduling
- One master CPU does all the scheduling.
- Other CPUs execute tasks assigned by the master.
2. Symmetric Scheduling
- Every CPU runs its own scheduler.
- More complex but scalable.
📊 Load Balancing Techniques
| Method | Description |
|---|---|
| Static | Load is distributed at start time. |
| Dynamic | Load is adjusted at runtime based on current load. |
| Task Migration | Move processes from busy CPUs to idle ones. |
🧠 Processor Affinity
- Scheduler keeps a process on the same CPU it previously ran on.
- Improves cache performance and reduces context switching.
✅ Advantages of Multiprocessor OS
- High performance due to parallel execution.
- Increased reliability (failure in one CPU doesn’t halt system).
- Better resource utilization.
- Scalability for complex computing needs.
❌ Challenges
- Synchronization overhead.
- Cache coherence problems.
- Increased complexity in scheduling and memory management.
🖥️ Examples of Multiprocessor Operating Systems
| System | Notes |
|---|---|
| Linux SMP | Supports multiple processors natively. |
| Windows NT/10 | Supports SMP and modern multicore systems. |
| UNIX (Solaris) | Designed for symmetric multiprocessor systems. |
| MacOS X | Supports multicore and SMP architectures. |
📌 Conclusion
A Multiprocessor Operating System is essential for efficiently managing multi-core or multi-CPU systems. Its design must address:
- Synchronization,
- Scheduling,
- Memory sharing,
- And inter-processor communication
to fully exploit hardware potential and deliver high performance and reliabilit