--- title: "DS vs centralized; layers of transparency" subject: "Distributed System" chapter: 1 key: "semester_7/distributed_system:ds-over-centralized-transparency" source: https://www.bctengineer.com/q/semester_7/distributed_system/ds-over-centralized-transparency site: BCT Engineering --- # DS vs centralized; layers of transparency Distributed System · Chapter 1: Introduction - Asked in: 2075 Chaitra, 4+4 marks - Video: [What are Distributed Systems | Centralized Systems | In 10 minutes](https://www.youtube.com/watch?v=NCptsas_rxc) — In 10 Minutes - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/distributed_system/ds-over-centralized-transparency - Whole chapter: https://www.bctengineer.com/md/semester_7/distributed_system/chapter-1 ## Question Why is a distributed system preferred over a centralized system? Explain the layers of transparency. ## Short answer Distributed systems are preferred for better price/performance, reliability, scalability, resource sharing, and geographic distribution without a single bottleneck. Transparency layers are network (access and location), system (migration, replication, concurrency, failure), and operational (performance and scaling). ## Answer #### Why a distributed system is preferred - **Better price/performance:** many low-cost machines are cheaper than one mainframe. - **Higher performance:** work is shared by parallel processing and load balancing. - **Reliability and availability:** failure of one node does not stop the whole system; replicas continue the service. - **Scalability:** capacity is increased by adding nodes, while a centralised system is limited by one machine. - **Resource sharing:** data and devices are shared across sites. - **Geographic distribution:** an organisation with branches (a bank) keeps data near its users, with low access delay. - **No single bottleneck or single point of failure.** #### Layers (levels) of transparency Transparency can be viewed at three layers. - **Network (access) layer:** *access transparency* (same operations for local and remote resources) and *location transparency* (names do not reveal location). - **System (resource management) layer:** *migration/relocation* (resources move), *replication* (copies), *concurrency* (shared use) and *failure* (recovery). - **Operational layer:** *performance* (reconfiguration to keep performance) and *scaling* (the system grows without changes to its structure). | Transparency | What is hidden | Example | |---|---|---| | Access | Differences in data representation and how a resource is accessed | Same call to read a local or remote file | | Location | Where the resource is physically located | URL does not show the server's place | | Migration | A resource may move to another location | A process moved to another host without the user noticing | | Relocation | Movement of a resource while it is in use | Mobile user keeps a call while moving between cells | | Replication | Existence of several copies | Many mirror servers behind one name | | Concurrency | Sharing of a resource by several users | Two users editing a database safely | | Failure | Failure and recovery of a component | Request is served by a backup when a server crashes | | Persistence | Whether the resource is in memory or on disk | Object is loaded from disk when needed | | Performance / scaling | System reconfigures to keep performance or grow | Load balancer adds servers | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is a distributed system more reliable than a centralized one? A. Failure of one node does not stop the whole system, and replication continues service B. It has a single point of failure C. It uses only one machine D. Its failure always stops all nodes Answer: A. No single point of failure means the remaining nodes continue to serve. (Key point: Reliability) 2. How is capacity increased in a distributed system compared with a centralized one? A. By replacing the single mainframe only B. By adding nodes, whereas a centralized system is limited by one machine C. It cannot be increased D. By removing nodes Answer: B. Incremental growth by adding machines is a key advantage. (Key point: Scalability) 3. Which transparency belongs to the network (access) layer? A. Access and location transparency B. Replication and failure transparency C. Performance and scaling transparency D. Migration and concurrency transparency Answer: A. The network layer covers access and location; system layer covers migration, replication, concurrency, failure; operational layer covers performance and scaling. (Key point: Layers of transparency) 4. Which transparencies belong to the operational layer? A. Access and location B. Migration and relocation C. Performance and scaling D. Concurrency and failure Answer: C. Performance (reconfiguration to keep performance) and scaling (growth without structural change) form the operational layer. (Key point: Operational layer) ## Related in Distributed System - [Centralized vs distributed; design issues](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Acentralized-vs-distributed) — Distributed System, chapter 1 - [Transparency properties of DS](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Ads-transparency-types) — Distributed System, chapter 1 - [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× - [Centralized vs Ricart-Agrawala algorithm](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Acentral-vs-ra-compare) — Distributed System, chapter 6 - [RPC vs RMI; modern RPC transparency](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Adifferentiate-rpc-modern-rpc) — Distributed System, chapter 2 - [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 - [Why serial transfer is preferred over parallel](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aserial-vs-parallel-preferred) — Instrumentation II, chapter 3 - [T/F: ACSR preferred over AAAC](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-acsr-vs-aaac) — Transmission and Distribution System Design, chapter 4 - [File system layers; linked list vs index](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Afs-layers-linked-list-vs-index) — Operating System, chapter 5 - [Distributed system in big data example](https://www.bctengineer.com/question.md?key=semester_8%2Fbig_data_technologies%3Adistributed-system-example) — Big Data Technologies, chapter 1