Lecture 1.pptx - DISTRIBUTED SYSTEMS Dr. Saddaf Rubab...

DISTRIBUTED SYSTEMS
Dr. Saddaf Rubab
NATIONAL UNIVERSITY OF SCIENCES AND TECHNOLOGY, PAKISTAN
SPRING, 2020
[email protected]

DISTRIBUTED SYSTEM

Definitions
1.
“A distributed system is a collection of independent computers that
appear to the users of the system as a single computer.”
[Tanenbaum]
2.
“A distributed system is a collection of autonomous computers
linked by a network with software designed to produce an
integrated computing facility.”
3.
“A system in which hardware or software components located at
networked computers communicate and coordinate their actions
only by message passing.” [Coulouris]
4.
“A system that consists of a collection of two or more independent
computers which coordinate their processing through the exchange
of synchronous or asynchronous message passing.”

ADVANTAGES OF DISTRIBUTED SYSTEMS OVER
INDEPENDENT PCS
Item Description
Data sharing Allow many users access to a common data base
Device sharing Allow many users to share expensive devices
Communication Make human-to-human communication easier
Flexibility Spread the workload over available machines in
the most cost effective way

DISTRIBUTED SYSTEM VS.
COMPUTER NETWORKS

Computer Network: Computers are connected generally in the same physical location, using
different styles e.g. Token ring, Star, Serial connection, etc. Also called as LAN, Local Area
Network.

We ll find it in a library, small offices, in the same building, computer labs, cyber cafe's etc,
etc. or computer network can be set up in your home

Also the autonomous computers are explicitly visible (have to be explicitly addressed)

Distributed System: Also can be considered as a type of computer network but in a much large
scale. Generally called as WAN,

Different computers are connected at different physical locations across cities, states, etc.

Using distributed systems, various computer programs can be run or executed remotely
irrespective of physical locations, so as to use the more memory and processing power of other
computers.

Existence of multiple autonomous computers is Transparent

DISTRIBUTED SYSTEMS VS. PARALLEL
COMPUTING

Parallel computing is related to tightly-coupled applications,
and is used to achieve one of the following goals:

Solve compute-intensive problems faster;

Solve larger problems in the same amount of time;

Solve same size problems with higher accuracy in the
same amount of time.

Distributed computing is related to loosely-coupled
applications, in which the goal (for distributed
supercomputing) is to solve problems otherwise too large or
whose execution may be divided on different components that
could benefit from execution on different architectures.

client-server,

peer-to-peer etc.

EXAMPLE 1
Automatic banking (teller machine) system

Each ATM has the ability to talk to all other networked
banks

Transactions can be done without regard to where a customer
or account is

Primary requirements: security and reliability.