Distributed System Concepts and Architectures

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Distributed System Concepts and Architectures

• Services
• Emailhbajpai1_at_student.gsu.edu

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Overview

• Service provider?
• Who are involved in providing the services?
• Types of services
• Basic services
• Fundamental services
• References

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Service provider?

• Operating system is the service provider. An
  operating system is a program that acts as an
  intermediary between the user of a computer and
  the computer hardware.

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Continued

• The purpose of an operating system is to provide
  an environment in which a user can execute
  programs in a convenient and efficient manner.
• Thus we can say that
• An OS is?

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Continued.

• Tool to make programmer's job easy
• Resource allocator
• Must be fair not partial to any process,
  specially for process in the same class
• Must discriminate between different class of jobs
  with different service requirements
• Control program
• Layered architecture

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Layer structure of a computer system
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Overview

• Service provider?
• Who are involved in providing the services?
• Types of services
• Basic services
• Fundamental services
• References

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Who are involved in providing the services?

• Since I am describing all the things here taking
  Unix as standard operating system. I would like
  to discuss here Shell and Kernel.

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Shell

• Unix command interpreter
• Interprets the first word of a command line as a
  command name
• Is a user program and not part of the kernel
• Redirection of input and output
• Background jobs

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Kernel

• Permanently resides in the main memory
• Controls the execution of processes by allowing
  their creation, termination or suspension, and
  communication
• Schedules processes fairly for execution on the
  CPU
• Allocates main memory for an executing process

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Continued

• File system maintenance
• Allows processes controlled access to peripheral
  devices such as terminals, tape drives, disk
  drives, and network devices.

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Overview

• Service provider?
• Who are involved in providing the services?
• Types of services
• Basic services
• Fundamental services
• References

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Basic Services

• Program execution
• I/O operations
• File-system manipulation
• Communications
• Error detection

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Program execution

• The system must be able to load a program into
  memory and to run that program. The program must
  be able to end its execution, either normally or
  abnormally (indicating error).

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I/O operations

• A running program may require I/O. This I/0 may
  involve a file or an I/O device. For specific
  devices, special functions may be desired (such
  as to rewind a tape drive, or to blank a CRT
  screen). For efficiency and protection, users
  usually cannot control I/0 devices directly.

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Continued

• Therefore, the operating system must provide a
  means to do I/O.

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File-system manipulation

• The file system is of particular interest.
  Obviously, programs need to read and write files.
  Programs also need to create and delete files by
  name.

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Communications

• In many circumstances, one process needs to
  exchange information with another process. Such
  communication can occur in two major ways. The
  first takes place between processes that are
  executing on the same computer

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Continued

• the second takes place between processes that are
  executing on different computer systems that are
  tied together by a computer network.
  Communications may be implemented via shared
  memory,

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Continued

• or by the technique of message passing, in which
  packets of information are moved between
  processes by the operating system.

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Error detection

• The operating system constantly needs to be aware
  of possible errors. Errors may occur in the CPU
  and memory hardware, in I/O devices and in the
  user program. For each type of error, the
  operating system should take the appropriate
  action to ensure correct and consistent
  computing.

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Overview

• Service provider?
• Who are involved in providing the services?
• Types of services
• Basic services
• Fundamental services
• References

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Fundamental services

• Primitive services
• Services by the system servers
• Value added services

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Primitive services

• Primitive services are those that must be
  implemented on kernel of each node in the system.
  In Distributed system when communication is done
  through message passing, a set of primitives for
  send and receive must be defined and implemented.
  Send and receive can be

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Continued.

• either synchronous or asynchronous. Synchronous
  communication, in addition to serving
  communication purposes, carries the side benefit
  of achieving internodes inter process
  synchronization.

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Services by the system servers

• The services which can be implemented anywhere in
  the system and performs the functions which is
  basic to the operation of a distributed system.
  To achieve transparency in Distributed System
  server mappes physical objects with logical
  system names.

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Continued.

• Name server
• Used to locate users, processes and machines.
• Directory Server
• It is used in conjunction with files and
  communication ports.
• Network server
• Name server translation, selection of paths,
  actual routing of information is done by network
  server.

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Value added services

• Services that are not needed in the
  implementation of a Distributed System But useful
  in supporting Distributed Application.
• It is Used To increase the computational
  performance and enhancement of fault tolerance or
  by need for cooperative activities.

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Continued.

• Group Server
• It manages the creation and termination of group
  activities. It is also responsible for Group
  addressing, communication, contain information
  about membership, member privileges and admission
  policies.
• Web server is also the good example of a value
  added server.

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References

• Distributed operating systems Algorithms, By
  Randy chow, Theodore Johnson. 1998
• Operating System Concepts 6th ed - Silberschatz
  Galvin, ch -3 operating System structure. 2003
• Advanced UNIX- A Programmers Guide, By Stephen
  Prata. 1997
• Computer science illuminated, second edition, By
  Nell dale, John Lewis. 2004
• http//ieeexplore.ieee.org/xpl/freeabs_all.jsp?arn
  umber138323

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Thankyou