Execution Environments for Distributed Computing Distributed Systems EEDC 3 4 3 3 0 Master in Computer Architecture, Networks and Systems - CANS Homework number: 6 Group number: EEDC-1 Group members: Umit Cavus Buyuksahin Ziwei Chen Faik Aras Tarhan {umit.cavus.buyuksahin, zwei.chen, faik. aras.tarhan}@ac.upc.edu
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Execution Environments for Distributed Computing
Distributed Systems
EEDC 34330
Master in Computer Architecture, Networks and Systems - CANS
● Centralized & Decentralized Systems● Differences from centralized & decentralized systems
○ Differences from centralized system○ Differences from decentralized system
● Examples● Conclusion
Definition
● A distributed system is a piece of software that ensures that: a collection of independent computers appears to its users as a single coherent system.
● Two aspects: (1) Independent computers and (2) single system => middleware.
Brief history
● 1945 ~ 1985○ ... computers were large and expensive○ ... no way to connect them○ ... all systems were Centralized Systems.
● Resource Sharing○ ... with Distributed Systems, it is easier for users to access remote resources
and to share resources with other users.● Openness
○ ... the openness of DS is determined primarily by the degree to which new resource-sharing services can be added and be made available for use by a variety of client programs.
● Transparency○ ... it hides the fact that the processes and resources are physically distributed
across multiple computers.● Scalability
○ ... a system is described as scalable if it remains effective when there is a significant increase in the number of resources and the number of users.
● Concurrency ○ ... there is a possibility that several clients will attempt to access a
shared resource at the same time.
Architecture
A distributed system organized as middlewareThe middleware layer extends over multiple machines, and
offers each application the same interface.
Centralized & Decentralized Systems
● Centralized Systems○ ... designed around a central
workstation
(+) simple and ease to maintain (-) non-scalable, single point of failure
● Decentralized Systems○ ... have exact opposite
characteristics of centralized sys.
(+) self-regulating, faster decision, scalability (-) difficult to manage
Differences From Centralized Systems
● Concurrency ... runs in concurrent processes on different processors
● Authority ... gives less authority to make decision
● Interaction ... more interaction between parts of organization
● Applicability ... best-suited to large industries and companies
Differences From Centralized Systems
● Communication ... from top to bottom, bottom to top as well as across
● Points of Control ... multiple points of control
● Points of Failure ... multiple points of failure
Differences From Decentralized Systems
● The difference is subtle.● The terms are probably used more or less interchangeably by
many.
● Decentralized systems ○ ...not necessarily 'distributed'○ ... does not have spread of functionality○ ... less resilient
Examples
● The world wide web – information, resource sharing● Clusters, Network of workstations● It is easier for users to access remote resources and to
share resources with other users like○ printers, files, Web pages, etc
● Distributed manufacturing system (e.g., automated assembly line)
● Network of branch office computers - Information system to handle automatic processing of orders
● Network of embedded systems● New Cell processor (PlayStation 3)
Examples - Internet
● The Internet is a vast interconnected collection of computer networks of many different types. [Coulouris et al, p.3]
● World’s largest client/server application
● Giant virtual disk
● Giant hyperlinked document
Examples - Centralized & Decentralized
● Napster○ on startup, client contacts central server○ reports list of files to central server○ return someone that stores the requested file○ get the file directly from peer
● BitTorrent○ run a tracker server to publish ○ contact centralized “tracker”