The client server model provides an effective general purpose approach to the

The client server model provides an effective general

This preview shows page 7 - 9 out of 22 pages.

The client-server model provides an effective general-purpose approach to the sharing of information and resources in distributed computing systems It is not only meant for use with the workstation-server model but also can be Implemented in a variety of hardware and software environments. The computers used to run the client and server processes need not necessarily be workstations and minicomputers. They can be of many types and there is no need to distinguish between them It is even possible for both the client and server processes to be run on the same computer. Moreover some processes are both client and server processes That is, a server process may use the services of another server, appearing as a client to the latter 5. A user has guaranteed response time because workstations are not used for executing remote processes. However the model does not utilize the processing capability of idle workstations. 4. Processor Pooled Model Processor-pool model is based on the observation that most of the time a user does not need any computing power but once m a while he or she may need a very large amount of computing power for a short time. Therefore, in the processor-pooled model the processors are pooled together to be shared by the users as needed. The pool of processors consists of a large number of microcomputer and minicomputers attached to the network. Each processor m the pool has its own memory to load and run a system program or an application program of the distributed computing system 7
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Unit 1 Architecture of Distributed Systems Figure 5: A distributed computing system based on processor-poor model In the pure processor's model, the processors m the pool have no terminals attached directly to them, and users access the system from terminals that are attached to the network via special devices. These terminals are either small diskless workstations or graphic terminals. A special server, called a run server, manages and allocates the processors in the pool to different users on a demand bases. When a user submits a Job for computation, an appropriate number of professors are temporarily assigned to the job by the run server. For Example If the user's computation job is the compilation of a program having n segments, Each of the segments can be compiled independently to produce separate releasable object files; n processors from the pool can be allocated to this job to compile all the segments in parallel. When the computation is completed, the processors are returned to the pool for use by other users In the processor-pool model there is no concept of a home machine. That is, a user does not log onto a particular machine but to the system as a whole This is in contrast to other models in which each user has a home machine (e.g., a workstation or minicomputer) onto which he or she logs and runs most of his or her programs they by default.
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