Distributed Operating system

1. DISTRIBUTED
OPERATING
SYSTEM
Sidra Naz 1743

2. CONTENT LIST
 Introduction
 Types of distributed OS
 Communication structure

3. INTRODUCTION
 Distributed operating system is a model where
distributed applications are running on multiple
computer linked by communication.
 These systems are referred as loosely coupled
systems where each processor has its own local
memory and processors communicate with one
another through various communication lines,
such as high speed buses or telephone lines.
 This system looks to its users like an ordinary
centralized operating system but runs on multiple,
independent CPU.

4. INTRODUCTION (CONT)
 The users of a true distributed system should not
know, on which machine their programs are running
and where their files are stored. LOCUS and
MICROS are the best examples of distributed
operating systems.

6. DISTRIBUTED SYSTEM

7. TYPES OF DISTRIBUTED OPERATING
SYSTEM
 There are two types of operating system
 Networking operating system
 Distributed operating system
 Advantages
 Disadvantages

8. NETWORKING OPERATING SYSTEM
 A Network Operating System runs on a server and
provides the server the capability to manage data, users,
groups, security, applications, and other networking
functions.
 The primary purpose of the network operating system is
to allow shared file and printer access among multiple
computers in a network, typically a local area network
(LAN), a private network or to other networks.
 Examples of network operating systems include
Microsoft Windows Server 2003, Microsoft Windows
Server 2008, UNIX and Linux.

9. DISTRIBUTED OPERATING SYSTEM
 Users not aware of multiplicity of machines.
 Data Migration – transfer data by transferring entire
file, or only portion of file.
 Computation Migration – transfer the computation,
rather than the data across file.
 Process Migration – execute an entire process, or parts
of it, at different sites.

10. COMMUNICATION STRUCTURE
 Communication Structure is the pattern of
interaction. The design of a communication network
must address four basic issues:
 Naming and Name Resolution
 Routing strategies
 Connection strategies
 Contention

11. Naming and Name Resolution
 The first component of network communication is the
naming of the systems in the network.
 Processes are generally identified by the pair host name,
identifiers.
 Domain name service (DNS) – specifies the naming
structure of the hosts, as well as name to address
resolution.

12. Routing strategies
 Fixed routing-A path from A to B is specified in advance
and does not change unless a hardware failure disables
it.
 Virtual routing-A path from A to B is fixed for the
duration of one session.
 Dynamic routing-The path used to send a message
from site A to site B is chosen only when a message is
sent.

13. Connection strategies:
 Circuit switching - A permanent physical link is
established for the duration of the communication.
 Message switching - If two processes want to
communicate, a temporary link is established for the
duration of one message transfer.
 Packet switching-One message is to be divided into a
number of packets. Each packet is sent to its destination
separately, and each therefore must include a source and
destination address with its data.

14. Contention:
 Techniques to avoid repeated collisions include:
 CSMA/CD - Carrier sense with multiple access
(CSMA); collision detection (CD) -Before transmitting a
message over a link, a site must determine whether
another message is currently being transmitted over that
link. If two or more sites begin transmitting at exactly the
same time, then they will register a CD and will stop
transmitting.
 Token passing - A unique message type, known as a
token, continuously circulates in the system, a site that
wants to transmit information must wait until the token
arrives and when the site completes its round of
message passing, it retransmits the token for other sites
to transmit messages.

15. Communication Protocol:
The communication network is partitioned into the
following multiple layers:
 Physical layer – handles the mechanical and electrical
details of the physical transmission of a bit stream.
 Data-link layer – handles fixed-length parts of packets,
including any error detection and recovery that occurred
in the physical layer.
 Network layer- The network layer is responsible for
providing connections and for routing packets in the
communication network, including handling the
addresses of outgoing packets, decoding the addresses
of incoming packets.

16.  Transport layer – responsible for low-level network
access and for message transfer between clients,
including partitioning messages into packets, controlling
flow, and generating physical addresses.
 Session layer – implements sessions, or process-to-
process communications protocols.
 Presentation layer – resolves the differences in formats
among the various sites in the network, including
character conversions.
 Application layer – The application layer is responsible
for interacting directly with users. This layer deals with file
transfer, and electronic mail.

17. ADVANTAGES
 Give more performance than single system
 If one pc in distributed system malfunction or corrupts
then other node or pc will take care of
 More resources can be added easily
 Resources like printers can be shared on multiple pc’s

18. DISADVANTAGES
 Security problem due to sharing
 Some messages can be lost in the network system
 Bandwidth is another problem if there is large data then
all network wires to be replaced which tends to become
expensive
 Overloading is another problem in distributed operating
systems
 If there is a database connected on local system and
many users accessing that database through remote or
distributed way then performance become slow
 The databases in network operating is difficult to
administrate then single user system