A recent trend in computer systems is to distribute computation among several processors. In contrast to the tightly coupled systems, the processors do not share memory or a clock. Instead, each processor has its own memory and clock. The processors communicate with one another through various communication lines These systems are usually referred to as loosely coupled systems, or distributed systems. The processors in a distributed system may vary in size and function. They may include small microprocessors, workstations, minicomputers, and large general-purpose computer systems. These processors are referred to by a number of different names, such as sites, nodes, computers, and so on, depending on the context in which they are mentioned.

1. Operating System 09
Distributed Operating System
Prof Neeraj Bhargava
Vaibhav Khanna
Department of Computer Science
School of Engineering and Systems Sciences
Maharshi Dayanand Saraswati University Ajmer

2. Distributed Operating Systems
• A recent trend in computer systems is to distribute
computation among several processors.
• In contrast to the tightly coupled systems, the processors do
not share memory or a clock.
• Instead, each processor has its own memory and clock.
• The processors communicate with one another through
various communication lines
• These systems are usually referred to as loosely coupled
systems, or distributed systems.
• The processors in a distributed system may vary in size and
function.
• They may include small microprocessors, workstations,
minicomputers, and large general-purpose computer systems.
• These processors are referred to by a number of different
names, such as sites, nodes, computers, and so on,
depending on the context in which they are mentioned.

3. Reasons for building distributed
systems
• Resource sharing.
• Computation speedup.
• Reliability.
• Communication.

4. Resource sharing.
• If a number of different sites (with different capabilities)
are connected to one another, then a user at one site
may be able to use the resources available at another.
• For example, a user at site A may be using a laser
printer available only at site B. Meanwhile, a user at B
may access a file that resides at A.
• In general, resource sharing in a distributed system
provides mechanisms for sharing files at remote sites,
processing information in a distributed database, printing
files at remote sites, using remote specialized hardware
devices (such as a high-speed array processor), and
performing other operations.

5. Computation speedup.
• If a particular computation can be partitioned
into a number of sub computations that can
run concurrently, then a distributed system
may allow us to distribute the computation
among the various sites — to run that
computation concurrently.
• In addition, if a particular site is currently
overloaded with jobs, some of them may be
moved to other, lightly loaded, sites. This
movement of jobs is called load sharing.

6. Reliability.
• If one site fails in a distributed system, the remaining
sites can potentially continue operating.
• If the system is composed of a number of large
autonomous installations (that is, general-purpose
computers), the failure of one of them should not affect
the rest.
• If, on the other hand, the system is composed of a
number of small machines, each of which is responsible
for some crucial system function (such as terminal
character I/O or the file system), then a single failure
may effectively halt the operation of the whole system.
• In general, if sufficient redundancy exists in the system
(in both hardware and data), the system can continue
with its operation, even if some of its sites have failed.

7. Communication.
• There are many instances in which programs
need to exchange data with one another on one
system.
• Window systems are one example, since they
frequently share data or transfer data between
displays.
• When many sites are connected to one another
by a communication network, the processes at
different sites have the opportunity to exchange
information.
• Users may initiate file transfers or communicate
with one another via electronic mail.

8. Distributed OS
• Distributed systems use multiple central
processors to serve multiple real-time
applications and multiple users.
• Data processing jobs are distributed among the
processors accordingly
• These are referred as loosely coupled systems or
distributed systems.
• Processors in a distributed system may vary in
size and function. These processors are referred
as sites, nodes, computers, and so on.

9. Advantages of distributed systems
• With resource sharing facility, a user at one site may be
able to use the resources available at another.
• Speedup the exchange of data with one another via
electronic mail.
• If one site fails in a distributed system, the remaining
sites can potentially continue operating.
• Better service to the customers.
• Reduction of the load on the host computer.
• Reduction of delays in data processing.

10. Assignment
• Explain Distributed Operating System