By, Naga Manojna Chintapalli. CHAPTER 2.2 TRANSPARENCY

OVERVIEW Evolution of Modern Operating systems Distributed Operating System Goals of DOS Definition of Transparency Types of transparency and their categorizations Distributed System issues & Transparencies DOS projects References

EVOLUTION OF MODERN OPERATING SYSTEMS 1 st Generation: Centralized Operating System 2 nd Generation: Network Operating System 3 rd Generation: Distributed Operating System 4 th Generation: Cooperative autonomous System

DISTRIBUTED OPERATING SYSTEM A collection of independent computers that appear to the system users as a single computer presenting a transparent view of a multiple computer system with distributed resources and control.

GOALS OF DOS Efficiency Flexibility Consistency Robustness

TRANSPARENCY “ Is defined as the concealment from the user and the application programmer of the separation of components in a DS, so that the system is perceived as a whole rather than as a collection of independent components ”

TRANSPARENCY (CONTD.,) Goal motivated by the desire to hide all irrelevant system-dependent details from the user, whenever possible. It is more important in distributed systems due to higher implementation complexities. Shielding the system-dependent information from the users is a trade-o ff between simplicity and e ff ectiveness.

TYPES OF TRANSPARENCY We have 10 types of transparencies. Let us see them in detail.

ACCESS TRANSPARENCY Access transparency - accessing both local and remote system objects in a uniform way.

LOCATION TRANSPARENCY Location transparency - no awareness of object locations. Sometimes called name transparency. Users of a Distributed System are not aware where a resource is physically located. The resources are referred by logical names. Example: area codes

MIGRATION TRANSPARENCY Migration transparency - ability to move an object to a di ff erent location without changing its name; also called location independence.

CONCURRENCY TRANSPARENCY Concurrency transparency - allow the sharing of objects without interference. Multiple users sharing a resource without any interference. It is similar to the time sharing concept.

REPLICATION TRANSPARENCY Replication transparency - consistency of multiple instances (or partitioning) of files and data

PARALLELISM TRANSPARENCY Parallelism transparency - parallel activities without users knowing how, when and where they are taking place.

FAILURE TRANSPARENCY Failure transparency - fault tolerance. Despite any failures in the system the task needs to be completed successfully i.e., it ensures graceful performance and minimum damages to the user.

PERFORMANCE TRANSPARENCY Performance transparency - attempts to achieve a consistent and predictable performance level even with changes of the system structure or load distribution.

SIZE TRANSPARENCY Size transparency - modularity and scalability. The system can expand in size without the knowledge of the user. It pertains to the incremental growth of the hardware.

REVISION TRANSPARENCY Revision transparency - vertical growth of the system This transparency refers to the software revisions which are not visible to the users.

CATEGORIZATION OF TRANSPARENCIES Transparencies can be categorized based on the goals of the distributed operating systems.

Concurrency Transparency Parallelism Transparency Performance Transparency Efficiency

Failure Transparency Replication Transparency Size Transparency Revision Transparency Robustness

Access Transparency Location Transparency Migration Transparency Size Transparency Revision Transparency Flexibility

Access Transparency Replication Transparency Performance Transparency Consistency

DISTRIBUTED SYSTEM ISSUES & TRANSPARENCIES

PROJECTS Example of projects based on distributed operating systems is E1  E1 is a distributed operating system project, based on the following concepts: object replication component model support Persistence  It Provides efficient access to the resources of computer network, implements a convenient programming model, isolating software developers from the intrinsic complexity of asynchronous distributed environment.  refer the link to know more about this project.

REFERENCES [1] A. S. Tanenbaum, “Distributed Operating Systems”, Prentice Hall, pp ,2001. [2] Y. Lu, “Distributed Operating Systems”, UNL. [3 ]R. Chow, T. Johnson, “Distributed Operating Systems & Algorithms”, Addison Weley, pp.29-32,1999. [4] B. Karp, “RPC & Transparency”,UCL Computer Science,2006. [5] Parallel and Distributed Operating System Group, MIT [6] IRIS: Infrastructure for Resilient Internet Systems [7] Systems)

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