--- title: "Heterogeneous model; DOS realization" subject: "Distributed System" chapter: 3 key: "semester_7/distributed_system:hetero-model-dos-realized" source: https://www.bctengineer.com/q/semester_7/distributed_system/hetero-model-dos-realized site: BCT Engineering --- # Heterogeneous model; DOS realization Distributed System · Chapter 3: Operating System Support - Asked in: 2070 Chaitra, 2+4 marks - Video: [Challenges in Distributed Systems : Heterogeneity Explained in Hindi](https://www.youtube.com/watch?v=lWwQzEfb05M) — 5 Minutes Engineering - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/distributed_system/hetero-model-dos-realized - Whole chapter: https://www.bctengineer.com/md/semester_7/distributed_system/chapter-3 ## Question Give an example of heterogeneous model of distributed application. How is distributed operating system realized in practical distributed systems? Explain. ## Short answer An online banking system with browser, mobile app, web server (Linux/Java), app server (Unix/C++), and mainframe database (Oracle) is heterogeneous. A true distributed OS is not used; instead middleware over network OS delivers naming, RPC, file system, and transactions, giving the illusion of a single system. ## Answer #### Example of a heterogeneous model of a distributed application A **heterogeneous** distributed application runs on components with different hardware, operating systems, languages and networks, joined by middleware. Example: an **online banking system**. ```text Browser (Windows) Mobile app (Android) \ / Web server (Linux, Java) | (CORBA / RMI / web services) Application server (Unix, C++) | Database (mainframe, Oracle) ``` - Clients on different devices, written in JavaScript or Kotlin. - A Java web server on Linux, and a C++ application server on UNIX. - An Oracle database on a mainframe. They communicate through middleware (CORBA with IDL, SOAP/REST web services), which converts data to a common format, so that the heterogeneity is hidden. #### Realisation of a distributed OS in practice A true distributed OS (one OS controlling all machines) is rarely used, because nodes are autonomous, heterogeneous and widely spread. Instead it is realised as **middleware over network operating systems**. 1. Every node runs its own local OS (kernel for local processes, memory, devices). 2. A middleware layer on top gives the global services of a distributed OS: naming, RPC/RMI communication, distributed file system, security, transactions, replication, load balancing. 3. Applications use the middleware API and see one system (transparency). 4. Microkernel-based designs put only basic IPC and scheduling in the kernel, and implement other services as servers that may be on any node. So the "distributed OS" is the combination of local OSs, the network and the middleware. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What makes the online banking example heterogeneous? A. All parts run Linux and Java B. Components use different hardware, OSs and languages joined by middleware C. It has only one client D. It runs on a single machine Answer: B. Browser, mobile app, Java web server, C++ application server and mainframe database differ in platform and language. (Key point: Heterogeneous application) 2. How does middleware such as CORBA or SOAP hide heterogeneity? A. It forces all nodes to use one language B. It removes the network C. It converts data to a common format D. It copies data to every node Answer: C. Middleware converts data to a common format so different platforms can communicate. (Key point: Role of middleware) 3. How is a distributed OS realised in practice? A. As middleware over network operating systems B. As one OS controlling all machines C. As hardware only D. As a single shared kernel Answer: A. A true DOS is rare; the global services are provided by middleware on top of local OSs. (Key point: DOS realisation) 4. In microkernel-based designs, what does the kernel contain? A. All services including file system B. Only basic IPC and scheduling, with other services as servers on any node C. Only device drivers D. Nothing Answer: B. Other services run as user-level servers that may be on any node. (Key point: Microkernel) ## Related in Distributed System - [Why NOS preferred over DOS](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Anos-vs-dos-realization) — Distributed System, chapter 3, asked 2× - [DOS; monolithic and microkernel](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Ados-monolithic-microkernel) — Distributed System, chapter 3 - [Operating system layers](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Aos-layers) — Distributed System, chapter 3 - [Heterogeneous vs homogeneous; CORBA](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Ahetero-homo-corba) — Distributed System, chapter 4 - [Homogeneous vs heterogeneous applications](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Ahomo-hetero-apps) — Distributed System, chapter 4 - [Autonomous vs distributed system](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Aautonomous-vs-distributed) — Distributed System, chapter 1 ## Related in other subjects - [ISI in baseband systems; ideal and practical solutions](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aisi-ideal-practical-solutions) — Communication Systems, chapter 6, asked 2× - [CMYK colour model and application](https://www.bctengineer.com/question.md?key=semester_8%2Fmultimedia_system%3Acmyk-colour-model) — Multimedia System, chapter 3 - [pipe(); semaphore in distributed systems](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Apipe-semaphore-distributed) — Operating System, chapter 3 - [Cascade form realization of second order system](https://www.bctengineer.com/question.md?key=semester_7%2Fdigital_signal_analysis_and_processing%3Acascade-form-3-4-1-8) — Digital Signal Analysis and Processing, chapter 4, asked 4×