Basic concepts of computer science. computer network signal information. Search on the World Wide Web

Applied informatics a set of information technologies used to process information related to practical activities. Technology activities related to the application of scientific research results for the creation and use of material and spiritual values. Informatization of society the process of creating optimal conditions to meet the information needs of citizens and organizations based on the use of information technologies. Computer universal device for information processing.

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LOCAL COMPUTER NETWORKS. TOPOLOGY. FEATURES OF BUILDING AND MANAGEMENT

Local computing network unites subscribers located at a short distance from each other (within 10-15 km). Typically, such networks are built within the same enterprise or organization.

Information systems built on the basis of local computer networks provide solutions to the following tasks:

• data storage;
• data processing;
• organizing user access to data;
• transfer of data and the results of their processing to users.

Computer networks implement distributed data processing. Here, data processing is distributed between two entities: the client and the server. During data processing, the client generates a request to the server to perform complex procedures. The server executes the request and sends the results to the client. The server provides storage of public data, organizes access to this data, and transmits the data to the client. This model of a computer network is called client-server architecture.

Based on the distribution of functions, local computer networks are divided into peer-to-peer and two-peer (hierarchical networks or networks with a dedicated server).

In a peer-to-peer network, computers have equal rights in relation to each other. Each user on the network decides for himself which resources of his computer he will provide for public use. Thus, the computer acts both as a client and as a server. Peer-to-peer sharing of resources is quite acceptable for small offices with 5-10 users, combining them into a work group.

A two-rank network is organized on the basis of a server on which network users register.

For modern computer networks, a mixed network is typical, combining workstations and servers, with some of the workstations forming peer-to-peer networks, and the other part belonging to two-peer networks.

The geometric connection diagram (physical connection configuration) of network nodes is called network topology. Exists a large number of options network topologies, the basic ones being tire, ring, star.

1. Tire.The communication channel connecting nodes into a network forms a broken line - a bus. Any node can receive information at any time, and transmit only when the bus is free. Data (signals) are transmitted by the computer to the bus. Each computer checks them, determining who the information is addressed to, and accepts the data if it is sent to it, or ignores it. If computers are located close to each other, then organizing a network with a bus topology is inexpensive and simple - you just need to lay a cable from one computer to another. Signal attenuation with increasing distance limits the length of the bus and, therefore, the number of computers connected to it.
   Bus topology problems arise when a break occurs (contact failure) anywhere in the country; network adapter one of the computers fails and begins to transmit signals with noise to the bus; you need to connect a new computer.
2. Ring.The nodes are connected into a closed curve network. Data transmission is carried out in only one direction. Each node, among other things, implements the functions of a repeater. He receives and transmits messages, and perceives only those addressed to him. Using a ring topology, you can connect a large number of nodes to the network, solving the problems of interference and signal attenuation using the network card of each node.
   Disadvantages of a ring organization: a break at any point in the ring stops the operation of the entire network; the message processing time is determined by the time of sequential operation of each node located between the ruler and the message recipient; Due to the flow of data through each node, there is a possibility of unintentional distortion of information.
3. Star.The network nodes are connected to the center by rays. All information is transmitted through the center, making it relatively easy to troubleshoot and add new nodes without interrupting the network. However, the cost of organizing communication channels here is usually higher than for a bus and ring.
   The combination of basic topologies - hybrid topology - provides a wide range of solutions that accumulate the advantages and disadvantages of the basic ones.

In addition to the problems of creating local computer networks, there is also the problem of expanding (merging) computer networks. The fact is that a computer network created at a certain stage of development of an information system may, over time, cease to satisfy the needs of all users. At the same time, the physical properties of the signal, data transmission channels and design features of network components impose strict restrictions on the number of nodes and the geometric dimensions of the network.

The following devices are used to connect local area networks.

1. Repeater- a device that provides amplification and filtering of a signal without changing its information content. As the signals travel along communication lines, they fade. Repeaters are used to reduce the effect of attenuation. Moreover, the repeater not only copies or repeats received signals, but also restores the characteristics of the signal: it amplifies the signal and reduces interference.

2.Bridge- a device that performs the functions of a repeater for those signals (messages) whose addresses satisfy pre-imposed restrictions. One of the problems of large networks is the tension network traffic(message flow on the network). This problem can be solved as follows. A computer network is divided into segments. The transmission of messages from segment to segment is carried out only purposefully if a subscriber of one segment transmits a message to a subscriber of another segment. A bridge is a device that restricts movement across a network and prevents messages from passing from one network to another without confirming the right to cross.

Bridges can be local or remote.

Local bridges connect networks located in a limited area within an existing system.

Remote bridges connect geographically dispersed networks using communication channels and modems.

Local bridges, in turn, are divided into internal and external.

Internal bridges are usually located on one computer and combine the function of a bridge with the function of a subscriber computer. Expansion of functions is carried out by installing an additional network card.

External bridges involve the use of a separate computer with special software treatment.

3.Router is a device that connects networks of different types, but uses the same operating system. This is, in fact, the same bridge, but with its own network address. Using the addressing capabilities of routers, hosts on a network can send messages to a router that are intended for another network. Routing tables are used to find the best route to any destination on the network. These tables can be static or dynamic.

4. Gateway- a special hardware and software complex designed to ensure compatibility between networks using different communication protocols. The gateway converts the presentation form and data formats when transmitting them from one segment to another. The gateway performs its functions at a level above the network level. It does not depend on the transmission medium used, but depends on the data exchange protocols used. Typically a gateway performs conversions between protocols.

With the help of gateways, you can connect a local area network to the host computer, as well as to a global area network.

1. In the book Excel sheet 1 give the name “Expense cash order”;

2. On the sheet “Cash receipt order” using Fig. 23.15 create an Expenditure Cash Order;

3. When creating a cash order, use merging and formatting of all necessary table elements;

4. Copy the created order to a Microsoft Word sheet;

Generalized structure of a computer network

Computer networks are the highest form of multi-machine associations. Let us highlight the main differences between a computer network and a multi-machine computing complex.

The first difference is the dimension. A multi-machine computing complex usually includes two, maximum three computers, located mainly in one room. A computer network can consist of tens and even hundreds of computers located at a distance from each other from several meters to tens, hundreds and even thousands of kilometers,

The second difference is the division of functions between computers. If in a multi-machine computing complex the functions of data processing, data transmission and system control can be implemented in one computer, then in computer networks these functions
distributed among various computers.

The third difference is the need to solve the problem of message routing in the network. A message from one computer to another in the network can be transmitted along different routes depending on the state of the communication channels connecting the computers to each other.

Integration into one complex of computer equipment, communication equipment and
Data transmission channels impose specific requirements on the part of each element of a multi-machine association, and also require the formation of special terminology.

Network subscribers- objects that generate or consume information on the network.

Subscribers networks can be individual computers, computer complexes, terminals, industrial robots, machines with numerical program controlled etc. Any network subscriber connects to the station.

Station- equipment that performs functions related to the transmission and reception of information.

The set of subscriber and station is usually called subscriber system. To organize the interaction of subscribers, a physical transmission medium is required.

Physical transmission medium- communication lines or space in which electrical signals propagate and data transmission equipment.

Based on the physical transmission medium, it is built communication network
which ensures the transfer of information between subscriber systems.

This approach allows us to consider any computer network as a collection
subscriber systems and communication network. Generalized structure of a computer network
is shown in Fig. 6.3.

Rice. 63. Generalized structure
computer network

Modern humanity practically cannot imagine its life without computers, but they appeared not so long ago. Over the past twenty years, computers have become an integral part of all areas of activity, from office needs to educational needs, thereby creating the need to develop capabilities and develop accompanying software.

Connecting computers into a network has made it possible not only to increase but also to reduce the cost of their maintenance, as well as to reduce time. In other words, computer networks have two goals: sharing software and hardware, as well as support open access to data resources.

Computer networks are built on the client-server principle. In this case, the client is an architectural component that, using a login and password, uses the capabilities of the server. The server, in turn, provides its resources to other network participants. This could be storage, creating a shared database, using input/output facilities, etc.

There are several types of computer networks:

Local;

Regional;

Global.

Here it would be fair to note on what principles the various

Organization of local computer networks

Typically, such networks bring together people who are at close range, so they are most often used in offices and enterprises for storing and processing data, transmitting its results to other participants.

There is such a thing as “network topology”. Simply put, this is a geometric diagram of connecting computers into a network. There are dozens of such schemes, but we will consider only the basic ones: tire, ring and star.

1. A bus is a communication channel that connects nodes into a network. Each node can receive information at any convenient time, and transmit only if the bus is free.
2. Ring. With this topology, the working nodes are connected sequentially in a circle, that is, the first station is connected to the second and so on, and the last is connected to the first, thereby closing the ring. The main disadvantage of this architecture is that if at least one element fails, the entire network is paralyzed.
3. A star is a connection in which the nodes are connected by rays to the center. This connection model comes from those distant times when computers were quite large and only the head machine received and

As for global networks, everything is much more complicated. Today there are more than 200 of them. The most famous of them is the Internet.

Their main difference from local ones is the absence of a main management center.

Such computer networks operate according to two principles:

Server programs located on network nodes that serve users;

Client programs located on user PCs and using server services.

Global networks give users access to various services. You can connect to such networks in two ways: through a dial-up telephone line and via a dedicated channel.

P/n Page
1. Components and main characteristics of computer systems 3
2. Importing data from other sources (DB, spreadsheets, text files). Data export. 14
References 16

Components and main characteristics of computer systems.
Content:
1. The concept of “computer systems”.
2. Computer.
3. Local and global networks.
The concept of “computer systems”.
Today the term “computer systems” means:
- directly the computer with the system and application installed on it software, and electronic media data;
- local and global computer networks.
As with any system, there are four basic characteristics of computer systems:
1. cost/performance ratio;
2. reliability and fault tolerance;
3. scalability;
4. software compatibility and portability.
Components computer system, as information, can perform 5 main functions (one or several at once):
1. obtaining information from external sources;
2. provision of information;
3. information storage;
4. transfer of information;
5. information processing.
Let's consider computers, local and global networks separately.
Computer.
Computers can be classified according to their areas of application and requirements:
1. Personal computers and workstations.
They appeared as a result of the evolution of minicomputers during the transition of the element base of machines with a small and medium degree of integration to large and ultra-large integrated circuits. PCs, due to their low cost, very quickly gained a good position in the computer market and created the preconditions for the development of new software oriented towards the end user. This is, first of all, “friendly” user interfaces", as well as problem-oriented environments and tools to automate the development of application programs.
The initial orientation of workstations towards professional users has led to the fact that workstations are well-balanced systems in which high performance is combined with a large amount of operational and external memory, high-performance internal buses, high-quality and high-speed graphics subsystem and a variety of input/output devices.
2. X-terminals.
They are a combination of diskless workstations and standard terminals. They occupy an intermediate position between personal computers and workstations.
A typical X terminal includes the following elements: screen high resolution; microprocessor: based on Motorola, RISC, etc.; separate graphics coprocessor; basic system programs; server software; variable local memory; ports for connecting a keyboard and mouse; peripheral devices.
3. Servers.
Multi-user commercial and business application systems require a transition to a client-server computing model and distributed processing. In a distributed client-server model, part of the work is done by the server and part by the user's computer. There are several types of servers, aimed at different applications: file server, database server, print server, computing server, application server. Thus, the type of server is determined by the type of resource it owns (file system, database, printers, processors, or application software packages).
On the other hand, there is a classification of servers, determined by the scale of the network in which they are used: server working group, departmental server or enterprise-scale server (corporate server).
Modern servers are characterized by: the presence of two or more central processors; multi-level bus architecture, as well as many standard input/output buses; technology support disk arrays RAID; support for symmetric multiprocessing mode, which allows you to distribute tasks across several central processors, or asymmetric multiprocessing mode, which allows you to allocate processors to perform specific tasks; run under UNIX and Windows operating systems; high degree of extensibility, flexibility and adaptability.
4. Mainframes.
This is synonymous with the concept of "mainstream computer". They can include one or more processors, each of which, in turn, can be equipped with vector coprocessors (operation accelerators with supercomputer performance). Architecturally, mainframes are multiprocessor systems containing one or more central and peripheral processors with shared memory, interconnected by high-speed data transfer routes. In this case, the main computing load falls on central processors, and peripheral processors ensure work with a wide range of peripheral devices.
5. Cluster architectures.
Cluster system is defined as a group of computers interconnected, representing a single information processing unit.
It has the following main characteristics: high availability; high throughput; ease of system maintenance: shared databases can be maintained from a single location, application programs can be installed only once on shared cluster disks and shared between all computers in the cluster; expandability: increasing the computing power of the cluster is achieved by connecting additional computers to it.
main feature The structure of a computer is that all computer devices exchange information through the system bus. Connected to the system bus CPU(or several processors), RAM, permanent and cache memory, which are made in the form of microcircuits. These components are mounted on the motherboard. External device cards are connected to the motherboard: video adapter, sound card, network card, etc. Depending on the complexity of the devices, other specialized processors may be located on these boards: mathematical, graphic, etc. Connected to the motherboard using wires HDD, floppy disk and optical disc reader.

Any Personal Computer contains the following main elements:
1. processor - a device that directly carries out the data processing process, main characteristics: clock frequency, word length, architecture;
2. system bus: a system of connected wires for transmitting information between computer devices connected to it; three types of information are transmitted along the bus: data, data addresses, commands;
3. motherboard with chipset;
4. inner memory: structurally performed in the form of modules, which are several microcircuits on small board and is intended for storing intermediate data that requires maximum fast access, main characteristics of memory: capacity, access time, cost of storing a unit of information;
5. external devices: divided into input devices, output devices and external storage devices, the main general characteristic of external devices can be the data transfer speed:
Device type Data transfer direction Transfer speed, KB/s
Keyboard input 0.01
Mouse input 0.02
Voice input input 0.02
Scanner input 200
Voice output output 0.06
Line printer output 1.00
Laser printer output 100
Optical disk storage 7800
Magnetic tape ZU 2000
Magnetic disk memory 25000
Floppy disk memory 40

Media using various physical principles are used as external memory in PCs:
- magnetic disks- these are the main media, characterized by the highest data transfer speed, but the reliability of storing information on magnetic disks is not very high;
- flexible magnetic disks: low cost and reliability;
- CDs: high capacity, low price, high reliability...
6. Monitor. A tool for displaying graphical and test information.
As general characteristics the following can be distinguished:
1. Performance (performance):
The speed of a computer is the speed at which it executes a certain sequence of requests (determined by the speed of the processor, the bandwidth of the data bus, or the speed of exchange with internal and external devices).
Towards modern computers difficult to apply, since the power of computers is growing both due to increased performance and due to the complication of architecture.
The basis for comparing different types of computers with each other is provided by standard performance measurement techniques.
The unit of measurement for computer performance is time: a computer that does the same amount of work in less time is faster. The execution time of any program is measured in seconds. Often performance is measured as the rate at which a certain number of events occur per second, so less time means more performance.
To measure the processor's operating time on a given program, a special parameter is used - CPU time, which does not include I/O latency or execution time of another program. Obviously, the response time seen by the user is the total execution time of the program, not CPU time. CPU time can be further divided into time spent by the CPU directly executing the user program, called user CPU time, and CPU time spent operating system to complete tasks requested by the program, and called system time CPU.
CPU time for a given program can be expressed in two ways: the number of clock ticks for a given program multiplied by the clock tick duration, or the number of clock ticks for a given program divided by the clock frequency.
An important characteristic often published in processor reports is the average number of clock cycles per instruction.
Thus, CPU performance depends on three parameters: clock cycle, average number of clock cycles per instruction, and the number of instructions executed. When two machines are compared, all three components must be considered to understand relative performance.
Alternative units of measurement
- MIPS - million commands per second. In general, this is the speed of operations per unit of time, i.e. for any given program, MIPS is simply the ratio of the number of instructions in the program to its execution time. However, using MIPS as a comparison metric faces three problems: CPU instruction set dependency, program dependency, can have the opposite effect on performance.
- MFLOPS. Typically, for scientific and technical tasks, processor performance is measured in MFLOPS (millions of floating point numbers per second, or millions of elementary arithmetic operations on floating point numbers performed per second). As a unit of measurement, MFLOPS is intended to measure floating-point performance only, and is therefore not applicable outside of this limited area.
Tests: INPACK (Livermore loops) is a set of fragments of Fortran programs, each of which is taken from real software systems; LINPACK is a package of Fortran programs for solving systems of linear algebraic equations; SPECint92 and SPECfp92 - based on real application programs a wide range of users, etc.
2. System throughput - determines the peak performance of a multiprogramming system, measured by the number of completed jobs per minute. Graph included in the report bandwidth system shows how it performs under different loads.
3. Reliability: time between failures and operating time.
4. Cost and ease of use.
5. Number of processors, volume random access memory, the amount of external memory.
6. Supported application and system software.
Local and global networks.
A computer network is a collection of computers connected by means of data transmission.
Depending on the remoteness of the computers included in the aircraft, networks are conventionally divided into local and global:
1. A local network is a group of interconnected computers located in a limited area, for example, in a building. The distance between computers in a local network can reach several kilometers. Local networks are usually deployed within an organization, which is why they are also called corporate networks.
2. Large networks are called global. A global network may include other global networks, local networks and individual computers. Global networks have almost the same capabilities as local ones. But they expand their scope.
To characterize the network architecture, the concepts of logical and physical topology are used:
1. Physical topology is the physical structure of the network, the method of physically connecting all hardware components of the network. There are several types of physical topology:
- Bus topology. The simplest one, in which the cable goes from computer to computer, connecting them in a chain. Such networks are cheaper, but if network nodes are located throughout the building, then using a star topology is much more convenient.
- With a physical star topology, each server and workstation is connected to a special device - a central hub, which connects a pair of network nodes - switching.
- If the network has many nodes, and many are located at a great distance from each other, then the cable consumption when using a star topology will be large. Additionally, only a limited number of cables can be connected to the hub. In such cases, a distributed star topology is used, in which several hubs are connected to each other.
- In addition to the types of connections considered, a ring-shaped topology can also be used, in which workstations are connected in a ring. This topology is practically not used for local networks, but can be used for global ones.
2. The logical topology of a network defines the way in which network devices transmit information from one node to the next. There are two types of logical topology: bus and ring.
In general, a network can be represented as a collection of the following elements:
1. Information processing nodes:
- Workstations.
- Servers and superservers: perform various service functions. There are different types of servers, which are determined by the type of service provided:
 A file server provides access to data stored in the external memory of the server. Thus, the file server is entrusted with all the tasks of data storage security, data retrieval, archiving, etc. The external memory of the server becomes a distributed resource, since it can be used by several clients.
 The print server organizes the sharing of the printer.
 A modem pool is a computer equipped with a special network card to which several modems can be connected. Thus, certain savings are achieved when, for example, ten computers operate using three modems.
 The proxy server not only uses a single connection to the Internet, but also provides its memory for storing temporary files, which speeds up work with the network.
 The main task of a router is to find the shortest path along which a message addressed to some computer will be sent. global network. A router is either a specialized computer or a regular computer with special software.
 The application server is used to execute programs that for some reason are impractical or impossible to execute on other network computers. An obvious reason may be insufficient performance of client computers. Another reason is the use of some standard libraries, copying which to each client computer is labor-intensive and, in addition, creates the possibility of inconsistency of the library version. Such a server must have a large amount of main and external memory and high performance.
 Database servers.
- Terminals.
2. Communication channels (medium for data exchange between nodes):
- Wireless optical communication lines.
- Fiber-optical communication lines.
- Radio channels, including satellite ones.
- Based on copper cable: shielded and unshielded twisted pair, thick and thin coaxial, etc. The main characteristics of a network cable are the data transfer speed and the maximum permissible length. Both characteristics are determined by the physical properties of the cable.
In building a modern information environment for an enterprise, an important role is played by the presence of an appropriate cabling system, which must be created in accordance with accepted standards, be universal, scalable, have a flexible structure and highly reliable.
In the early 90s, the concept of Structured Cable System, providing a range of services for data transmission, voice and video information. The need to define standards was caused by the desire to ensure the interoperability of equipment from various manufacturers and, in general, to protect the funds invested in the creation of communications infrastructure.
3. Switching equipment (can also be called information processing nodes, but at the transport level):
- Sockets, connectors, panels, etc.
- Modems. This is a computer communication device telephone lines. By telephone network any data can be transmitted only in analog form. Data from the computer comes in digital form. The modem's job is to convert digital data into analog form and vice versa.
- Network cards. They are additional boards installed on motherboard PC. Connect to the network card network cables. The network card determines the type of local network.
- Concentrators.
- Switches.
- Routers.
- Gateways.
The main characteristics of networks are:
1. Message delivery time. Defined as the statistical average time from the moment a message is transmitted to the network until the message is received by the recipient.
2. Network performance. Represents the total performance of the servers.
3. Cost of data processing. The cost of data processing is determined both by the cost of the facilities used for processing, and by the delivery time and network performance.
4. Network type. Determined by the structure and operating principles of the data transmission network, which are described by the protocol. A protocol is a system of rules that define the format and procedures for transmitting data over a network.
5. Data transfer speed. Currently, two main network speeds are widely used for local networks - 10 Mbit/s in accordance with the IEEE 802.3 (10Base-T) standard and 100 Mbit/s in accordance with the IEEE 802.12 (100Base-TX) standard, as well as 1000 Mbit/s (1Gbit/s) in accordance with IEEE 802.3ab (1000Base-TX) standard.
6. Reliability of the network.
Importing data from other sources (DB, spreadsheets, text files). Data export.
In connection with the growing importance and role of information in the life of modern society, the significantly increased volume of stored, received and processed information, the basic task of data structuring has arisen (information presented in a form that allows automating its collection, storage and further processing by a person or information media).
The term structuring means bringing to unified representations and formats.
Since the tasks and requirements for automated systems are different, different forms of information presentation have been developed and are used.
The following forms used in information systems can be distinguished (in order of complexity):
1. Text files. They are either a sequence of alphabets and control characters (formats with the extension “*.txt”, characterized by different encodings), or binary files that allow you to complicate the structure of the text by adding graphic and other objects (files “*.doc”, “*.rtf”, etc.).
2. Spreadsheets. They represent a collection of homogeneous structures that have fields that are identical in meaning.
3. Database files. They are built on the basis of spreadsheets interconnected at the level file systems represented by one or many files.
For efficient work with information it is necessary to ensure data exchange between text files, spreadsheets and databases, as well as provide print output and visual perception.
Data exchange consists of import and export:
1. Data import - provision information system necessary data to the external environment in a certain format.
2. Data export – receipt and integration of data from the external environment by the information system in a format understandable to it while maintaining integrity.
In this case, it is very important that the source and recipient of information use the same data presentation formats, otherwise graphics will be perceived as text, music as video, which will entail a violation of the integrity of the system, which will try to misuse this data. In the context of modern data banks, this can cause enormous damage.
Therefore, this problem is solved today in two ways:
1. Development of standards for the presentation of information both at the state level and at the level of commonly used applications and DBMS, for example:
- graphic files: “*.bmp”, “*.jpg”, “*.tiff”, “*.gif”, etc.;
- video files: “*.avi”, “*.mpeg”, “*.asf”, etc.;
- database files: “*.db”, “*.mdb”, “*.dbf”, etc.;
2. Development of object technologies.

Bibliography
1. Inside the Internet Methods of searching for information, Kuznetsov S.D., - Educational book +. - M. – 2001.
2. Global television news networks in the information market, Orlova V.V., - RIP-Holding. –M. - 2003
3. Global business and information Technology. Modern practice and recommendations, Popov V.M., Marshavin R.A., - Finance and statistics. –M. - 2001.
4. Computer science. Textbook. –M. - 1999.