--- title: "Define DS and its requirements" subject: "Distributed System" chapter: 1 key: "semester_7/distributed_system:define-ds-requirements" source: https://www.bctengineer.com/q/semester_7/distributed_system/define-ds-requirements site: BCT Engineering --- # Define DS and its requirements Distributed System · Chapter 1: Introduction - Asked in: 2076 Chaitra, 2+8 marks; 2072 Kartik, 2+6 marks; Model question (asked 3 times) - Video: [1.1 Define distributed systems and their goals](https://www.youtube.com/watch?v=TP__yw30ax4) — OU Education - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/distributed_system/define-ds-requirements - Whole chapter: https://www.bctengineer.com/md/semester_7/distributed_system/chapter-1 ## Question Define Distributed System (DS). Explain the requirements to successfully implement DS to suit modern computing. ## Short answer A distributed system is a collection of independent computers connected by a network and middleware that appears as a single coherent system. Requirements include resource sharing, transparency, openness, scalability, concurrency, fault tolerance, heterogeneity support, security, QoS, and manageability/mobility. ## Answer #### Definition A **distributed system** is a collection of independent computers, connected by a network and running distribution middleware, that appears to its users as a single coherent system. Its components communicate and coordinate their actions only by passing messages (Tanenbaum; Coulouris). Examples: the World Wide Web, banking networks with ATMs, cloud services, online reservation systems. #### Requirements for modern computing To succeed in modern computing a distributed system must satisfy the following. 1. **Resource sharing:** hardware, data and services are available to all authorised users. 2. **Transparency:** access, location, migration, replication, concurrency and failure are hidden so users see one system. 3. **Openness:** published interfaces and standards (IDL, protocols) let different vendors' components work together and let the system be extended. 4. **Scalability:** it must grow in size (users and resources), geography and administration without loss of performance. Use replication, caching, partitioning and avoid centralised services. 5. **Concurrency:** many users and processes access resources at once, so synchronisation (locks, transactions) is required. 6. **Fault tolerance and availability:** detect failures, mask them by redundancy and recover. 7. **Heterogeneity support:** different hardware, OS, networks and languages are linked by middleware. 8. **Security:** confidentiality, integrity, authentication, access control and protection against denial of service. 9. **Performance and quality of service:** low latency, high throughput and timeliness, especially for multimedia. 10. **Manageability and mobility:** easy to configure, monitor and extend; supports mobile and ubiquitous devices. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which statement correctly defines a distributed system? A. Computers sharing one memory and clock to run one program B. Independent networked computers with middleware that appear as a single coherent system, coordinating by message passing C. A single mainframe serving many terminals D. A network of computers that each run unrelated programs Answer: B. Distributed system components are independent, networked and coordinate only by messages, yet present one system view. (Key point: Definition) 2. In which ways must a distributed system be able to scale without loss of performance? A. Size (users and resources), geography and administration B. Only in the number of CPUs C. Only in disk capacity D. Only in the number of programming languages supported Answer: A. Scalability covers size, geographic spread and administrative domains. (Key point: Scalability requirement) 3. Why is synchronisation (locks, transactions) required in a distributed system? A. Because there is only one user B. Because clocks are perfectly synchronised C. Many users and processes access shared resources at the same time D. To make messages travel faster Answer: C. Concurrent access to shared resources needs locks or transactions to keep data consistent. (Key point: Concurrency requirement) 4. How are different hardware, operating systems, networks and languages linked in a distributed system? A. By rewriting every program in one language B. By middleware C. By removing the network D. By using only one vendor's hardware Answer: B. Middleware provides a uniform layer hiding heterogeneity. 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