transp-dist-OS1 - DISTRIBUTED SYSTEMS Computer Node...

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DISTRIBUTED SYSTEMS A distributed system refers to a system that consists of several computers that do not share a memory or a clock and communicate with each other by exchanging messages over a communication network. A distributed operating system runs on multiple independent computers but appears to its users as a single machine. Motivations 1. Improved price/performance -- with the exception of certain special computation intensive applications, equivalent computing power may be obtained with a network of workstations at a much lower cost than a traditional time-sharing system. 2. Resource sharing -- requests of services may be satisfied using hardware/software resources on other computers on the communication network. 3. Enhanced performance -- concurrent execution of tasks and load distributing can lead to improved response time. 4. Improved reliability and availability -- fault tolerance can be achieved through the replication of data and services. 5. Modular expandability -- new hardware and software resources can be added without replacing the existing resources. Computer Node Computer Node Computer Node Computer Node Computer Node Communication Network Architecture of a Distributed System Legend : Each computer node has its own memory and runs its own OS.
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Issues in distributed operating systems 1. Global knowledge -- global state of the system is hard to acquire due to the unavailability of a global memory and a global clock and the unpredictability of message delays. 2. Naming -- the directory of all the named objects in the system (services, files, users, printers, etc.) must be maintained to allow proper access. Both schemes of replicated directories and partitioned directories have their strengths and weaknesses. 3. Scalability -- any mechanisms or approaches adopted in a system must not result in badly degraded performance when the system grows. 4. Compatibility -- the interoperability among the resources in a system must be an integral part of the design of a distributed system. Three levels of compatibility exist: 5. Process synchronization -- especially difficult in distributed systems due to the lack of shared memory and a global clock. 6. Resource management -- refers to schemes and methods devised to make local and remote resources available to users in an effective and transparent manner. Three 7. Security -- two issues are relevant: authentication (verifying claims) & authorization (deciding the and authorizing the proper amount of privileges). 8. Structuring -- defines how various parts of the operating system are organized. Three general organizations exist: Monolithic kernel -- a traditional method with the kernel consisting of all the services to be provided in the system which may be wasteful in a distributed environment. Collective kernel structure
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This note was uploaded on 04/11/2010 for the course CECS 526 taught by Professor Nguyen,t during the Spring '08 term at CSU Long Beach.

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transp-dist-OS1 - DISTRIBUTED SYSTEMS Computer Node...

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