فریاد Faryad

At the heart of the Internet Protocol (IP) portion of TCP/IP is a concept called the Internet address. This 32-bit coding system assigns a number to every node on the network. There are various types of addresses designed for networks of different sizes, but you can write every address with a series of numbers that identify the major network and the sub-networks to which a node is attached. Besides identifying a node, the address provides a path that gateways can use to route information from one machine to another.

Although data-delivery systems like Ethernet or X.25 bring their packets to any machine electrically attached to the cable, the IP modules must know each other"s Internet addresses if they are to communicate. A machine acting as a gateway connecting different TCP/IP networks will have a different Internet address on each network. Internal look-up tables and software based on another standard - called Resolution Protocol - are used to route the data through a gateway between networks.

Another piece of software works with the IP-layer programs to move information to the right application on the receiving system. This software follows a standard called the User Datagram Protocol (UDP). You can think of the UDP software as creating a data address in the TCP/IP message that states exactly what application the data block is supposed to contact at the address the IP software has described. The UDP software provides the final routing for the data within the receiving system.

The Transmission Control Protocol (TCP) part of TCP/IP comes into operation once the packet is delivered to the correct Internet address and application port. Software packages that follow the TCP standard run on each machine, establish a connection to each other, and manage the communication exchanges. A data-delivery system like Ethernet doesn"t promise to deliver a packet successfully. Neither IP nor UDP knows anything about recovering packets that aren"t successfully delivered, but TCP structures and buffers the data flow, looks for responses and takes action to replace missing data blocks. This concept of data management is called reliable stream service.

After TCP brings the data packet into a computer, other high-level programs handle it. Some are enshrined in official US government standards, like the File Transfer Protocol (FTP) and the Simple Mail Transfer Protocol (SMTP). If you use these standard protocols on different kinds of computers, you will at least have ways of easily transferring files and other kinds of data.

Conceptually, software that supports the TCP protocol stands alone. It can work with data received through a serial port, over a packet-switched network, or from a network system like Ethernet. TCP software doesn"t need to use IP or UDP, it doesn"t even have to know they exist. But in practice TCP is an integral part of the TCP/IP picture, and it is most frequently used with those two protocols.

The application layer is the only part of a communications process that a user sees, and even then, the user doesn"t see most of the work that the application does to prepare a message for sending over a network. The layer converts a message"s data from human-readable form into bits and attaches a header identifying the sending and receiving computers.

Linux has its roots in a student project. In 1992, an undergraduate called Linus Torvalds was studying computer science in Helsinki, Finland. Like most computer science courses, a big component of it was taught on (and about) Unix. Unix was the wonder operating system of the 1970s and 1980s: both a textbook example of the principle of operating system design, and sufficiently robust to be the standard OS in engineering and scientific computing. But Unix was a commercial product (licensed by AT&T to a number of resellers), and cost more than a student could pay.

Data mining is simply filtering through large amounts of raw data for useful information that gives businesses a competitive edge. This information is made up of meaningful patterns and trends that are already in the data but were previously unseen.

The most popular tool used when mining is artificial intelligence (AI). AI technologies try to work the way the human brain works, by making intelligent guesses, learning by example, and using deductive reasoning. Some of the more popular AI methods used in data mining include neural networks, clustering, and decision trees.

Neural networks look at the rules of using data, which are based on the connections found or on a sample set of data. As a result, the software continually analyses value and compares it to the other factors, and it compares these factors repeatedly until it finds patterns emerging. These patterns are known as rules. The software then looks for other patterns based on these rules or sends out an alarm when a trigger value is hit.

Clustering divides data into groups based on similar features or limited data ranges. Clusters are used when data isn"t labelled in a way that is favorable to mining. For instance, an insurance company that wants to find instances of fraud wouldn"t have its records labelled as fraudulent or not fraudulent. But after analyzing patterns within clusters, the mining software can start to figure out the rules that point to which claims are likely to be false. Decision trees, like clusters, separate the data into subsets and then analyze the subsets to divide them into further subsets, and so on (for a few more levels). The final subsets are then small enough that the mining process can find interesting patterns and relationships within the data.

Once the data to be mined is identified, it should be cleansed. Cleansing data frees it from duplicate information and erroneous data. Next, the data should be stored in a uniform format within relevant categories or fields. Mining tools can work with all types of data storage, from large data warehouses to smaller desktop databases to flat files. Data warehouses and data mars are storage methods that involve archiving large amounts of data in a way that makes it easy to access when necessary.

When the process is complete, the mining software generates a report. An analyst goes over the report to see if further work needs to be done, such as refining parameters, using other data analysis tools to examine the data, or even scrapping the data if it"s unusable. If no further work is required, the report proceeds to the decision makers for appropriate action.

The power of data mining is being used for many purposes, such as analyzing Supreme Court decisions, discovering patterns in health care, pulling stories about competitors from newswires, resolving bottlenecks in production processes, and analysing sequences in the human genetic makeup. There really is no limit to the type of business or area of study where data mining can be beneficial.

The basic components of a computer system, the input, the output, the memory, and the processor operate only in response to commands from the control unit. The control unit operates by reading one instruction at a time from memory and taking the action called for by each instruction. In this way it controls the flow between main storage and the arithmetic-logical unit.

A control unit has the following components:

 It is common practice in computer science for the words ‘computer‘ and ‘processor‘ to be used interchangeably. More precisely, ‘computer‘ refers to the central processing unit (CPU) together with an internal memory. The internal memory or main storage, control and processing components make up the heart of the computer system. Manufacturers design the CPU to control and carry out basic instructions for their particular computer.

It also performs some kinds of logical operations such as comparing or selecting information. All the operations of the ALU are under the direction of the control unit.

Programs and the data on which the control unit and the ALU operate, must be in internal memory in order to be processed. Thus, if located on secondary memory devices such as disks or tapes, programs and data are first loaded into internal memory.

 Until the mid1960s, digital computers were powerful, physically large and expensive. What was really needed though, were computers of less power, a smaller memory capacity and without such a large array of peripheral equipment. This need was partially satisfied by the rapid improvement in performance of the semiconductor devices (transistors), and their incredible reduction in size, cost and power; all of which led to the development of the minicomputer or mini for short. Although there is no exact definition of a minicomputer, it is generally understood to refer to a computer whose mainframe is physically small, has a fixed word length between 8 and 32 bits and costs less than U.S. $100,000 for the central processor.

 Many minicomputers are used merely for a fixed application and run only a single program. This is changed only when necessary either correct errors or when a change in the design of the system is introduced. Since the operating environment for most minis is far less varied and complex than large mainframes, it goes without saying that the software and peripheral requirements differ greatly from those of a computer which runs several hundred ever-changing jobs a day. The operating systems of minis also usually provide system access to either a single user or to a limited number of users at a time. Since many minis are employed in real-time processing, they are usually provided with operating systems that are specialized for this purpose.

 For example, most minis have an interrupt feature which allows a program to be interrupted when they receive a special signal indicating that any one of a number of external events, to which they are preprogrammed to respond, has occurred. When the interrupt occurs, the computer stores enough information about the job in process o resume operation after it has responded to the interruption. Because minicomputer systems have been used so often in real-time applications, other aspects of their design have changed; that is, they usually possess the hardware capability to be connected directly to a large variety of measurement instruments, to analog and digital converters, to microprocessors, and ultimately, to an even larger mainframe in order to analyze the collected data.

Large computer systems, or mainframes, as they are referred to in the field of computer science, are those computer systems found in computer installations processing immense amounts of data. These powerful computers make use of very high-speed main memories into which data and programs to be dealt with are transferred for rapid access. These powerful machines have a larger repertoire of more complex instructions which can be executed more quickly. Whereas smaller computers may take several steps to perform a particular operation, a larger machine may accomplish the same thing with one instruction.

These computers can be of two types: digital or analog. The digital computer or general-purpose computer as it is often known, makes up about 90 per cent of the large computers now in use. It gets its name because the data that are presented to it are made up of a code consisting of digits single character numbers. The digital computer is like a gigantic cash register in that it can do calculations in steps, one after another at tremendous speed and with great accuracy. Digital computer programming is by far the most commonly used in electronic data processing for business or statistical purposes.

Really powerful computers continue to be bulky and require special provision for their housing, refrigeration systems, air filtration and power supplies. This I because much more space is taken up by the input/output devices the magnetic tape and disk units and other peripheral equipment than by the electronic components that do not make up the bulk of the machine in a powerful installation . The power consumption of these machines is also quite high , not to mention the price that runs into hundreds of thousands of dollars . The future will bring great developments in the mechanical devices associated with computer systems . For a long time these have been the weak link , from the point of view of both efficiency and reliability .

In order to use computers effectively to solve problems in our environment, computer systems are devised. A ‘system‘ implies a good mixture of integrated parts working together to form a useful whole. Computer systems may be discussed in two parts.

Like all machines, a computer needs to be directed and controlled in order to perform a task successfully. Until such time as a program is prepared and stored in the computer’s memory, the computer ’knows’ absolutely nothing, not even how to accept or reject data. Even the most sophisticated computer, no matter how capable it is, must be told what to do. Until the capabilities and the limitations of a computer are recognized, its usefulness cannot be thoroughly understood.