🌐 Introduction to Distributed Operating System
A Distributed Operating System (DOS) is a type of OS that manages a group of independent computers and makes them appear to users as a single coherent system.
It coordinates and manages hardware and software resources across multiple computers, enabling resource sharing, computation speedup, reliability, and scalability.
🧠 Definition
A Distributed Operating System is software that manages a collection of independent computers and makes them appear to users as a single computer.
✳️ Characteristics of Distributed Operating Systems
| Characteristic | Description |
|---|---|
| Transparency | Hides the complexity of the distributed environment from users. |
| Resource Sharing | Enables sharing of files, devices, and computation among systems. |
| Concurrency | Supports multiple users/processes running simultaneously across nodes. |
| Scalability | Easy to scale up by adding more machines. |
| Fault Tolerance | The system continues to function even if some components fail. |
| Openness | Easily integrated with other hardware/software platforms via standard APIs. |
| Security | Ensures secure communication and data access across networks. |
🏛️ Architecture of Distributed Operating Systems
1. Client-Server Model
- Clients request services (e.g., file access).
- Servers provide services (e.g., file servers, compute servers).
🔁 Example: NFS (Network File System)
2. Peer-to-Peer Model (P2P)
- All nodes are equal; each acts as both client and server.
- More robust and fault-tolerant than client-server.
🔁 Example: BitTorrent
3. Hybrid Model
- Combines client-server and P2P.
- Used in systems where critical services are centralized but still support peer interactions.
4. Middleware-Based Architecture
- Uses a middleware layer between OS and applications.
- Provides communication, naming, synchronization, and security services.
🧩 Types of Transparency in DOS
| Type | Description |
|---|---|
| Access Transparency | Remote and local resources appear the same to users. |
| Location Transparency | Users don’t need to know the physical location of resources. |
| Concurrency Transparency | Multiple users can access shared resources concurrently. |
| Replication Transparency | System hides the existence of multiple copies of data. |
| Failure Transparency | The system continues to operate despite failures. |
| Migration Transparency | Processes can move between nodes without affecting execution. |
❗ Issues in Distributed Operating Systems
1. Communication
- Requires reliable message-passing between distributed components.
- Protocols like TCP/IP, RPC (Remote Procedure Call), RMI (Remote Method Invocation) used.
2. Resource Management
- Resources (CPU, memory, I/O devices) are distributed.
- System must allocate them efficiently while maintaining fairness and transparency.
3. Process Management
- Processes may run on different machines.
- OS must manage creation, scheduling, synchronization, and termination across nodes.
4. Security
- Ensuring secure communication and access control is challenging in a distributed setting.
- Threats include eavesdropping, impersonation, and data tampering.
5. Fault Tolerance
- The system should detect and recover from hardware/software failures without major disruption.
- Redundancy, checkpointing, and replication techniques are used.
6. Naming
- Global naming scheme needed to identify resources and processes across the network.
- Must be unique, location-independent, and persistent.
7. Synchronization
- Clocks on different systems may not be synchronized.
- Time-stamping, logical clocks (Lamport Clock, Vector Clock) are used.
8. Transparency
- All complexities (location, migration, replication, concurrency) should be hidden from the user.
9. Load Balancing
- Dynamically distribute workload among various nodes to avoid bottlenecks and improve performance.
🖥️ Examples of Distributed Operating Systems
| System | Description |
|---|---|
| Amoeba | Developed at Vrije University – supports P2P model. |
| Mach | Microkernel-based distributed OS. |
| Chorus | Focuses on real-time and embedded systems. |
| LOCUS | Provides transparent access to distributed files. |
| Plan 9 | Developed by Bell Labs – everything is a file. |
| Google File System (GFS) | Proprietary DFS for Google’s distributed applications. |
📌 Conclusion
A Distributed Operating System is a powerful and scalable way to harness the power of multiple machines as a single system. It must address key issues like transparency, synchronization, security, resource allocation, and fault tolerance to function effectively.