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عندي بحث او بمعنى اصح تقرير عن النظم الموزعة واود مساعدتكم لي فيه ...
*حسنات وسيئات النظم الموزعة*
وجدت هذه
لل DITRIBUTED SYSTEM
ADV
Cheaper and easier to build lots of simple computers
Easier to add power incrementally
Machines may necessarily be remote, but system should work together
Higher availability - one computer crashes, others carry on working
Better reliability - store data in multiple locations
More security - each piece easier to secure to right level.
DIS
Its difficult to design a good distributed system: there are a lot of problems in getting ``good'' characteristics, not the least of which is people
وهذه ..
ولكنا لل DITRIBUTED COMPUTING
[edit] Goals and advantages
There are many different types of distributed computing systems and many challenges to overcome in successfully designing one. The main goal of a distributed computing system is to connect users and resources in a transparent, open, and scalable way. Ideally this arrangement is drastically more fault tolerant and more powerful than many combinations of stand-alone computer systems.
[<a href="http://en.wikipedia.org/w/index.php?title=Distributed_computing&action=edit§ion=3" target="_blank">edit] Openness
Openness is the property of distributed systems such that each subsystem is continually open to interaction with other systems (see references). Web services protocols are standards which enable distributed systems to be extended and scaled. In general, an open system that scales has an advantage over a perfectly closed and self-contained system. Openness cannot be achieved unless the specification and documentation of the key software interface of the component of a system are made available to the software developer.
Consequently, open distributed systems are required to meet the following challenges:
Monotonicity Once something is published in an open system, it cannot be taken back. Pluralism Different subsystems of an open distributed system include heterogeneous, overlapping and possibly conflicting information. There is no central arbiter of truth in open distributed systems. Unbounded Nondeterminism Asynchronously, different subsystems can come up and go down and communication links can come in and go out between subsystems of an open distributed system. Therefore the time that it will take to complete an operation cannot be bounded in advance. </a>
[<a href="http://en.wikipedia.org/w/index.php?title=Distributed_computing&action=edit§ion=4" target="_blank">edit] Drawbacks and disadvantages
See also: Fallacies of Distributed Computing </a>
[<a href="http://en.wikipedia.org/w/index.php?title=Distributed_computing&action=edit§ion=5" target="_blank">edit] Technical issues
If not planned properly, a distributed system can decrease the overall reliability of computations if the unavailability of a node can cause disruption of the other nodes. Leslie Lamport famously quipped that: "A distributed system is one in which the failure of a computer you didn't even know existed can render your own computer unusable."[1]
Troubleshooting and diagnosing problems in a distributed system can also become more difficult, because the analysis may require connecting to remote nodes or inspecting communication between nodes.
Many types of computation are not well suited for distributed environments, typically owing to the amount of network communication or synchronization that would be required between nodes. If bandwidth, latency, or communication requirements are too significant, then the benefits of distributed computing may be negated and the performance may be worse than a non-distributed environment.
واحترت وش احط .. وهل فيه اختلاف بين المصطلحين ..
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STRIBUTED SYSTEM ISSUE:
واحترت ايضا بين هذا ..
Elements of a Distributed System
Another way to view a system...
Communications system
Messages
Machines
Processes on Machines
Programs
People
وهنا
Design issues: Transparency
High level: hide distribution from users
Low level: hide distribution from software
– Location transparency:
users don’t care where resources are
– Migration transparency:
resources move at will
– Replication transparency:
users cannot tell whether there are copies of resources
– Concurrency transparency:
users share resources transparently
– Parallelism transparency:
operations take place in parallel without user’s knowledge
Design issues
Reliability
– Availability: fraction of time system is usable
• Achieve with redundancy
– Reliability: data must not get lost
• Includes security
Performance
– Communication network may be slow and/or unreliable
Scalability
– Distributable vs. centralized algorithms
– Can we take advantage of having lots of computers?
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DISTRIBUTED SYSTEMS APPLICATIONS
هل هو المقصود بها TYPES ام EXAMPLE
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