DECENTRALIZED COMPUTING

A decentralized computer system, as opposed to a centralized one, is collection of autonomous computers which communicate with one another to perform a common service. A decentralized system might occupy a single room, but more typically decentralized systems have geographic and organizational diversity.

The world telephone system is the biggest and best example of a decentralized system. It consists of thousands of computers, and almost a billion terminals. Some of the nodes of the system are tiny local PBX's while others are quite large, able to handle many calls per second. Different parts of the system are operated by cooperating organizations with different hardware, different languages and different ideologies. They have agreed to protocols which allow direct dialing from anywhere to anywhere and the consequent automatic routing and billing.

Other examples of decentralized systems can be found in the world travel industry system, inter-connecting travel agents with hotels, airlines, and other reservation systems, and the emerging electronic financial system, connecting financial institutions, businesses and governments.

These systems have the following common features:

* Diverse organizations and organizational procedures,

* Diverse computer architectures, both hardware and software,

* Diverse terminal types,

* Diverse system sizes, from tiny to large, and

* Diverse site environments.

Decentralized computing is a trend in modern day business environments. On the other hand centralized computing was prevalent during the early days of computers. Decentralized computing involves allocation of resources, both hardware and software, to each workstation. In contrast, centralized computing exists when the majority of functions are carried out, or obtained from a remote centralized location.

A decentralized computer system has many benefits over a conventional centralized network. Desktop computers have advanced so rapidly, that their potential performance far exceeds the requirements of most business applications. This results in most desktop computers remaining idle (in relation to their full potential). A decentralized system can utilize the potential of these systems to maximize efficiency. However, it is debatable whether these networks increase overall effectiveness.

All computers have to be updated individually with new software, unlike a centralized computer system. Decentralized systems still enable file sharing and all computers can share peripherals such as printers and scanners as well as modems, allowing all the computers in the network to connect to the internet.

A collection of decentralized computers systems are components of a larger computer network, held together by local stations of equal importance and capability. These systems are capable of running independently of each other.

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DEBUGGING

Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware thus making it behave as expected.

The debugging skill of the programmer is probably the biggest factor in the ability to debug a problem, but the difficulty of software debugging varies greatly with the programming language used and the available tools, such as debuggers. Debuggers are software tools which enable the programmer to monitor the execution of a program, stop it, re-start it, set breakpoints, change values in memory and even, in some cases, go back in time. The term debugger can also refer to the person who is doing the debugging.

Generally, high-level programming languages, such as Java, make debugging easier, because they have features such as exception handling that make real sources of erratic behaviour easier to spot. In lower-level programming languages such as C or assembly, bugs may cause silent problems such as memory corruption, and it is often difficult to see where the initial problem happened. In those cases, memory debugger tools may be needed.

In certain situations, general purpose software tools that are language specific in nature can be very useful. These take the form of static code analysis tools. These tools look for a very specific set of known problems, some common and some rare, within the source code. All such issues detected by these tools would rarely be picked up by a compiler or interpreter, thus they are not syntax checkers, but more semantic checkers.

Often the first step in debugging is to attempt reproduce the problem. This can be a non-trivial task

After the bug is reproduced, the input of the program needs to be simplified to make it easier to debug. For example, a bug in a compiler can make it crash when parsing some large source file. However, after simplification of the test case, only few lines from the original source file can be sufficient to reproduce the same crash

After the test case is sufficiently simplified, a programmer can use a debugger to examine program states (values of variables, the call stack) and track down the origin of the problem. Alternatively tracing can be used. In simple case, tracing is just a few print statements, which output the values of variables in certain points of program execution.

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