Lecture №1 "The concept of information, the overall characteristics of the processes of collection, transmission, processing and accumulation of information"
Information. Types of information. Properties of information. Representation of data in computer. Notation. Positional viewing systems. Translation of numbers from one number system to another. Coding information. Units of information measurement. Transfer information. Data processing. Data storage. Magnetic memory. Optical memory.
Information
Term "information" comes from the Latin word "Informatio"What does it mean, clarification, presentation. Despite the widespread dissemination of this term, the concept of information is one of the most debated in science. Currently, science is trying to find general properties and patterns inherent in a multifaceted concept. informationBut as long as this concept largely remains intuitive and receives various semantic filling in various branches of human activity.
In everyday life, for example , Information is called any data or information that anyone interests. "Inform" in this sense means "Report something, unknown earlier.
The current scientific understanding of the information very accurately formulated Norbert Wiener, the Father of Cybernetics. Namely: information is the designation of the content obtained from the outside world in the process of our adaptation to it and the adaptation of our senses to it.
People exchange information in the form of messages. The message is a form of presentation of information in the form of speech, texts, gestures, views, images, digital data, graphs, tables, etc.
In cases where they say on automated work with information through any technical devices, Usually, first of all, you are not interested in the message, but by how many characters this message contains.
In relation to computer processing, the data is understood to understand some sequence of symbolic designations (letters, numbers, coded graphic images and sounds, etc.), carrying the semantic load and the form presented in a clear computer. Each new character in such a sequence of characters increases the information volume of the message.
Types of information
Information may exist in the form:
Texts, drawings, drawings, photos;
Light or sound signals;
Radio waves;
Electrical and nerve impulses;
Magnetic records; etc.
Items, processes, phenomena of material or intangible properties, considered from the point of view of their information properties, are called information objects.
Information can be:
All these processes associated with certain information operations are called information processes.
Properties of information
Information is reliable if it reflects the true state of affairs. Invalid information can lead to incorrect understanding or making incorrect solutions.
Reliable information over time can become inaccurate, as it possesses the property to be outdated, that is, it ceases to reflect the true state of affairs.
Information fullIf it is enough to understand and making decisions. Both incomplete and redundant information restrains making decisions or may entail errors.
Accuracy of information It is determined by the degree of its proximity to the real state of the object, the process, phenomena, etc.
Value value It depends on how important it is to solve the problem, as well as on how future it will find application in any kind of human activities.
Only timely received information Can bring expected benefits. Equally undesirable as a premature submission of information (when it cannot yet be assimilated) and its delay.
If valuable and timely information is incomprehensible, it can become useless.
Information it becomes clearIf it is expressed by the language on which those who are intended for this information.
Information should be presented in the available (by level of perception) form. Therefore, the same questions are presented in different ways in school textbooks and scientific publications.
Information on the same issue you can summarize (compressed, without insignificant parts) or extensively (in detail, verbose). Brief information is needed in reference books, encyclopedias, textbooks, all kinds of instructions.
Presentation of data in computer
All information in the computer is stored as bits sets, that is, combinations 0 and 1. The numbers are represented by binary combinations in accordance with the numeric formats taken to work in this computer, and the character code establishes the correspondence of letters and other symbols of binary combinations.
For numbers there are three numeric formats:
Binary with a fixed point;
Binary with floating comma;
Binary-coded decimal (BCD).
Floating semicolons are processed on a special coprocessor (FPU - Floating Point Unit), which, starting with MP I486, is part of the bis microprocessor. The data in it is stored in 80-bit registers.
Notation.
The method of representing the image of arbitrary numbers with a certain final set of characters, let's call the number system.
In everyday practice, we use, as a rule, a decimal number system.
The number systems are customary to ...
1. Positional.
2. Unexication.
3. Symbolic.
Symbolic. In these systems, each number is put in line with its character. These systems do not find wide use by virtue of their natural limitations (alchemy, coded messages) - countless characters, which is required for the image of all possible numbers. Therefore, these systems from consideration will be omitted.
To present information in memory of the computer (both numeric and non-numeric), a binary method of coding is used.
Elementary memory cell of the computer has a length of 8 bits (bytes). Each byte has its own number (it is called address). The greatest sequence of the bit, which computer can process as a whole, called machine word. The length of the machine word depends on the discharge of the processor and may be equal to 16, 32, 64 bits, etc.
Binary-decimal coding
In some cases, when presenting numbers in the memory of the computer, a mixed binary-decimal "number system" is used, where it is necessary for storing each decimal sign. A decimal format designed to store integers with 18 significant numbers and occupies 10 bytes in memory (senior of which is iconic), uses this particular option.
Representation of integers in the additional code
Another way to represent integers - additional code. The range of values \u200b\u200bdepends on the number of memory bits, allocated to store them. For example, the values \u200b\u200bof the Integer type (all names of the data types here and below are presented in the form in which they are accepted in the TURBO PASCAL programming language. In other languages, such data types are also there, but may have other names) lie in the range from -32768 ( -2 15) to 32767 (2 15 - 1) and 2 bytes (16 bits) are given to storage; Longint type - in the range from -2 31 to 2 31 - 1 and placed in 4 bytes (32 bits); type Word - in the range from 0 to 65535 (2 16 - 1) (used 2 bytes), etc.
As can be seen from examples, the data can be interpreted as numbers with sign, so I. no sign. In the case of representing the value with the sign, the leftmost (senior) discharge indicates a positive number if it contains zero, and on a negative, if the unit.
In general, the discharges are numbered on the right left, starting with 0. The following is shown the numbering of the bit in a two-byte machine word.
Additional code a positive number coincides with his direct code. The direct code of an integer can be obtained as follows: the number is translated into a binary number system, and then its binary recording on the left is complemented by such a number of insignificant zeros, how much does the data type require that the number belongs to.
For example, if the number 37 (10) \u003d 100101 (2) declared the value of the type Integer ( sixteenybitated with sign), then its direct code will be 0000000000100101, and if the value of type Longint ( thirtyDeddvukhbito with sign), then his direct code will be. For a more compact record, a hexadecimal view of the code is more often used. The obtained codes can be rewritten according to 0025 (16) and 00000025 (16).
Additional code of a whole negative number can be obtained according to the following algorithm:
- record the direct code of the module number;
- invert it (replace units with zeros, zeros - units);
- add to the inverse code unit.
For example, we will write an additional number code -37, interpreting it as a type of Longint type (thirty-lucid with a sign):
- the direct number of the number 37 is;
- inverse code;
- additional code or FFFFFFFDB (16).
Upon receipt of the number according to its additional code, it is primarily necessary to determine its sign. If the number turns out to be positive, then simply translate its code into a decimal number system. In the case of a negative number, the following algorithm must be performed.
Any information is in the computer as sequence byte. In the bytes themselves there is no information about how they need to be interpreted (numbers / text signs / graphic image). In any case, the information is encoded as a sequence of 0 and 1, i.e. positive integer binary numbers (The number is written using two digits - 0/1). Their interpretation depends on which program and what action with them makes at this particular point. If the program has a sequence of teams oriented to work with numbers, the bytes are considered as numbers. If the program is assumed to be an action with text data, the bytes are interpreted as conditional numeric codes that indicate text signs.
I. Numbness
Any number is a multiple amount of the amount (for example, 168 \u003d 100 + 60 + 8 \u003d 1 10 2 + 6 10 1 + 8 10 0), i.e. number - sequence of coefficients in the degrees of the number 10 \u003d\u003e if we have a number d \u003d a 1 a 2 ... a n(A 1 A 2 ... a n - numbers), then d \u003d a 1 10 n - 1 + a 2 10 n-2 + ... a n 10 0.
Briefly similar amounts are written as follows: n.
d \u003d Σ a i 10 n-i
The number 10 is the basis of the decimal number system, if you take another number as a base, then we get another number of numbers recording, i.e. another number system.
The number system is set to the value of the base and many numbers. Numbers - Special signs used to record numbers. Their number must be equal to the value of the base.
Any number can be represented in various number systems, these views will be strictly (Mutually unambiguously) match each other.
For example, we define a 16-relica number system: the base \u003d 16 \u003d\u003e should be 16 digits (0-15) \u003d 1,2,3,4,5,6,7,8,9, a, b, c, d , E, F. Here a-F - numbers 10,11,12,13,14,15. Such designations are used due to the fact that the numbers cannot be recorded using other numbers, otherwise it will be confused in reading numbers. We write, as it will look like in this number system decimal number 168, having in mind the general law of the recording of the number, as well as the fact that here the base is 16, we have: 168 (10) \u003d a 16 1 + 8 16 0 \u003d\u003e A8 (16 ).
Arithmetic actions in any number system are performed similarly to how it is done in a 10-riche system. Only the value of the foundation.
For example, in the 8-richery system + 15 \u003d 1 8 1 + 5 8 0 \u003d\u003e + 13
14 = 1 8 1 + 4 8 0 => = 12
In the computer, all data are presented in a binary number system. For example, the number 5 in binary form is recorded as 101. Similarly, the binary number 1111 corresponds to the decimal number 15: 1111 (2) \u003d 1 2 3 + 1 2 2 + 1 2 1 + 1 2 0
Those. Four bits can be represented by no more than 16 decimal numbers (0-15).
As a brief recording when viewing or fixing binary data in the memory of the computer, a 16-riche surger system is used. Programs providing the "direct" person's work with a computer memory when interacting with it automatically convert a binary representation of data into 16-rich and back. Any given, recorded in 1 pate, seems to be only two 16-round figures, the first of which corresponds to the first four bits, and the second digit is the second four of the bits.
This form of representation of binary numbers (data) in memory of the computer is a compromise between a person and its concepts about convenience and a computer, where all information is only available in binary form.
II. Data Types and Representations
One byte (8 bits) can be represented by 256 positive integers (0-255). This type of data is called singleless whole without sign.
Numbers exceeding 255 require more byte for its presentation. Types are used to work with them:
- double-byte whole sign - ensure the representation of entire positive numbers (0-65535)
- four-prohibited whole signs - ensure the representation of entire positive numbers (0 - ≈4.2 billion)
The above types suggest that the number should only be positive \u003d\u003e called "no sign". They differ in memory, which is given to the storage of the number. Such types are used for numerical coding of text signs, color, intensity of graphic dots, numbering elements, etc.
To work with integers, which may not only be positive, but also negative, use types:
- single-way whole with a sign
- double-byte integers with a sign
- four-prohibited integers with a sign
They differ in the amount of memory, which is assigned to the storage of each number.
At the heart of the presentation of both positive and negative numbers lies the following principle: the total number of numerical codes, possible for a given number of bytes (for example, for single-byte - 256), is divided into half, one half is used to represent positive numbers and zero, the other - negative numbers . Negative numbers are represented as an addition to the total number of numeric codes. For example, for a single-byte number (-1) \u003d 255, (-2) - 254, etc. Up to 128, which denotes the number (-128) \u003d\u003e Single-way integer with a sign allows you to work with integers from (-128) to 127, two-byte - from (- 32768) to 32767, four-proof - from (≈ - 2.1 billion. ) to 2.1 billion (2147483648).
Numbers are used to represent numeric data with which arithmetic actions are manufactured.
When interacting with programs, the following are used. data types:
- whole shortiy (Short)
- whole ordinary (Integer)
- long (Long Integer)
- equality with single accuracy (Float / Real)
- double-accuracy (DoubleFloat / Real)
- symbol (string, text) (Char)
- logical (Logikal)
Whole short, whole ordinary and whole long - Types, respectively, a single-byte integer with a sign, double-byte integer with a sign, four-prohibited integer with a sign.
In computer science when recording numbers as a sign dividing fractional and integer, not a comma, but a point (for example, 68.314). This point fixes the position after which the fractional part is indicated. Changing the location of the point leads to a change in the number \u003d\u003e This kind of recording (recording format) of real numbers is called fixed Point Format.
The real number of floating point consists of 2 parts:
- mantissa
- order
They are divided by a special sign (E, D). Mantissa is a real number with a fixed point, the order is defined by an integer indicating which degree should be erected by the number 10 so that when you multiply the Mantissa to get a number that is meant. For example, 68.314 in this format can be written as 6.8314e + 1 \u003d 0.68314e + 2 \u003d 683.14e-1, which means 6.8314 10 1 \u003d 0.68314 10 2 \u003d 68.314 10 -1.
With this type of recording, the location of the point is not fixed, its position in the mantissa is determined by the value of order. Mantissa and order may have a sign. If Mantissa module<1, причем первая цифра не равна 0, то такой вид записи вещественного числа с плавающей точкой называется normalized (0.68314e + 2).
In the computer, the real number is presented in a floating point format in a normalized format. Mantissa and order are located in adjacent bytes, the separator (E, D) is absent.
Usually distinguish the number with single and double accuracy. In the first case, when entering or output, the number as a divider of the mantissa and order is indicated E.. In the memory of the computer, such a number is usually occupied by 4 bytes. In the second case, as a separator - D.In memory of the computer, the dual accuracy is usually 8 bytes. This type provides a significantly greater calculation accuracy than single accuracy.
Symbolic datacompiled from separate text signs. Each sign is submitted in the memory of the computer with a specific numerical code. For numeric coding of text characters, special coding tables are used (single-path, double-byte, etc.). This refers to the type of integer without a sign that is used for numerical coding. Different programs can be based on different tables \u003d\u003e Test document created using the same program, it can not be read using another.
Values logical type Take only two values:
- True. (true)
- False(False)
These can be applied logical operations, the main of which are and. (and), or. (or), not. (negation). And, OR -K two logical values \u200b\u200b(A\u003e C and a \u003d b). Not - to one logical value (not a \u003d b). The result of expression with logical data (logical expression) is a logical value. The result of the operation and \u003d True is only in one case, if both values \u200b\u200b\u003d true. The result of the OR \u003d FALSE operation is only in one case, if both quantities \u003d false. The NOT operation changes the value of the logical value.
In mixed expressions, the priority of arithmetic operations, then in comparison, last time - in logical operations. Among them are the greatest priority from the NOT operation, then - and, after - OR.
Files and storage
Any information object (a separate document, a separate program) stored on the disk and the name is file. File information (their name, size, date and time of creation, place of placement on disk, etc.) is stored in directories. Catalog - Table, in each row of which provides information about any file or other directory. Catalog \u003d file (except root) special type. When writing files to the disk, the information about them is automatically written to those directories that the user indicated. Conditionally for brevity speech say: "Copy the file from the directory in the directory", "Create a directory directory", "Delete the file in the catalog", etc. However, it does not really happen, because there are no directories or files in the catalogs, there is only information about them.
When the disk is generated on it, a directory is automatically created, which is called root. It occupies a certain place of fixable size on the disk. Its name consists of 2 signs: Disc name and colon.
In the root directory, you can create other directories that are called subdirectories or the catalogs of the first level of the hierarchy. In turn, the directories of the first level of the hierarchy can create the directories of the second level, etc. Thus formed hierarchical (tree) file structure on disk. Custom catalogs - files. Each file or directory has a name consisting of two parts, separated by a point. Left part - name, right - expansion. Expansion along with a point you can not specify. The name is permissible to specify no more than 8 characters (short name) or not more than 256 characters (long name). In extension - no more than 3 characters. The standard is considered to use only Latin letters, numbers and an underscore sign. It is recommended to operate files to refer to the expansion, and directories without expansion.
If you want to use any file, you must specify in which directory this file is located. This is done by specifying the path (route) to the directory file file.
Route (Path) is a list of directories as they are nesting (from external to internal), separated by the name of the reverse line (\\ - reverse slash). When you specify the files, the route is specified before its name, and then through \\ - the file name (for example, C: \\ Windows \\ Win.com - means that the Win.com file is located in the Windows directory, which is located in the root directory of the C disk C). This entry is called full file specification. Brief includes only the name of the file. The user-generated directories and files are placed when recording on their disk memory location. Files can be recorded by parts in different parts of the disk. In the process of recording, the file is automatically divided into such parts, and each of them is written to the place that is currently at the moment. These parts are called clusters. The cluster size depends on the amount of disk memory, it usually takes several sectors. In connection with this principle of recording, the entire disk area seems to be divided into such clusters, and they are used to record files. File reading is also made by parts in size in one cluster: the file is collected from individual parts recorded in different parts of the disk. This method of storage of files is carried out using the so-called file Placement TablesFat. It is created on each disk automatically when it is generated and is used to memorize the storage locations of the file parts. Fat cells are numbered, starting with "0", and correspond to the parts of the disk size of 1 cluster. Each cell may contain 0 (indicates that the corresponding cluster is free), the next cluster number of this file or a special numeric code indicating the end of the cluster chain for this file. To represent the numbers in the FAT, data types are used without a sign. Depending on the number of bits used to represent each number, 16 bit FAT (16 bit) are distinguished, 32 bit FAT (32 bit). As a special code that means the end of the cluster chain, a maximum number is used, which can be represented in the FAT cell. For 16 discharge, such a number is 65535 (in hexadecimal form - fffff). Programs that ensure the view and adjustment of FAT show this code on the screen in the text form (E OF). The directory contains information about the file and in particular the cluster sequence number from which the file begins. This information, together with the information contained in the FAT (references to the following clusters), is used to search and read files.
Computer networks
I. Home Features
Computer network - A set of interconnected through channels of information transmission of computers providing users with means of exchanging information and collective use of resources (hardware, software, information).
Types of networks:
- local - The main distinctive feature is that, as a rule, all computers associated with it are associated with a single communication channel. The distance between computers is up to 10 km (when using wired communication), up to 20 km (communication radio channels). Local networks associate a computer of one or several nearby buildings of one institution.
- global - For them, they are characterized by a variety of communication channels and the use of satellite channels, allowing to connect communication nodes and computers located at a distance of 10-15 thousand km from each other. Usually have a nodal structure, consist of subnets, each of which includes communication nodes and communication channels. Communication nodes ensure the efficiency of the network operation, computers, local networks, large computer, etc. are connected to them.
- intraseni. - Combine users working in one organization. The part uses the ability of existing local and global networks. Such a network can associate computers that are in both the building and in different places in the world.
The network has publicly available computers that provide information or computing users. Server A computer used for this purpose or place (in global networks) can be called, where you can send a request for any service. Such a place can be a computer server, a local network, a large computer, etc.
User computers can work on networks in two modes:
Mode workstation- The computer is used not only to send a request to the server and receiving information from it, but also for processing this information
Mode terminal -the latter is not performed: information processing is carried out on the server, and only the result of this processing is sent to the user.
A computer-server in its capabilities is significantly superior to workstations and is equipped with a variety of network cards ( adapters), providing connection to networks. Complex programs that provide network work - network software.It defines the type of services, the execution of which is possible in this network. Currently common 2 Main concept Building such software:
- "File Server Concept" - It is based on the fact that network software should provide many user information resources in the form of files \u003d\u003e The server in such a network is called filelov, and network software - network operational system. Its main part is posted on the file server, and its small part is installed on workstations, called sheath. The shell performs the role of the interface between the resource programs and the file server. Such a server is a file repository used by all users. In this case, both programs and data files on the file server are automatically moved to the workstation, where this data is processed.
- "Client-server architecture" - In this case, network software consists of software systems 2 classes:
- servers program - so called software systems that provide the server
- client software - software systems providing customer users
The operation of these classes is organized as follows: Customer programs send requests to the server-server, the main processing of the data is performed on the computer-server, and only the results of the query is sent to the user's computer.
In local networks, the concept of the first type with one file server is usually used. Global main is the Client Server Architecture.
The presentation of information and transferring it over the network is made in accordance with standard agreements. A set of such standard agreements is called protocol.
II.Tipology of the local network
Network typology - Logic connection diagram of computer communication channels (computers).
Most often in local networks are used 3 main typology:
- monocanal
- ring
- star-shaped
Using the information transfer channel connecting network nodes at the physical level is determined by the protocol called by access. These access methods are implemented by appropriate network cards (adapters). Such adapters are installed in each network computer and provide transmission and reception information through communication channels.
Monocanal typology - Used an unclosed communication channel to which all computers are connected. It is called monocanal-tire (total tire).
Terminator
The terminal is used to connect to open network cables, designed to absorb the transmitted signal. In such typology, as a rule, an access method with a pre-listening channel is used to determine whether it is free.
Ethernet(Speed \u200b\u200b- 10 Mbps) - the name of the access method. Access method can be used Fast Ethernet (speed - 100Mbps / s)
Sustainability of individual nodes
The main disadvantages of typology:
Cable break leads to the inability to the entire network
Significant reduction in network bandwidth with significant volumes traffic(- information transmitted over the network)
Ring Tyology
 |
Uses a connected ring as a communication channel, consisting of segments. Segments are connected by special devices - reputers (repeaters). The repeater is designed to connect network segments.
The main method of access here is token Ring - the access method with the transmission of the marker.
There is a central communications node that combines all network computers. The active center fully manages network computers. The access method is usually based on the use of the marker (for example, ArcNet with a speed of 2 Mbps information transmission). In addition, Ethernet and Fast Ethernet access methods can be implemented.
The main advantages of typology:
Convenience in terms of computers interaction
Easy to change and build network
The main disadvantages of the network:
If the active center fails, the entire network fails
III. Global network Structure
Between Networks is possible to exchange information, to ensure such communication uses of firewall interaction, called bridges, routers and gateways. This is a special computer in which two or more network adapters are installed, each of which provides communication with one network. The bridge is used to connect networks with the same type of intranet communication channels. The router connects the network of the same species, but by various intranet communication channels. Gateways are used to connect networks of different types to communicate networks with various computer systems (for example, a local network is a large computer, a local network - a global network, a specific personal computer - a global network).
The global network includes a communication subnets to which local networks, workstations and user terminals are connected, as well as server computers. Communication subnet consists of information transmission channels and communication nodes. Communication components are designed to quickly transfer information over the network, selecting the optimal information transfer route, etc., i.e. ensure the efficiency of the network functioning as a whole. Such a node is either a special hardware device or a specialized computer with respective software.
Servers and users connect to global networks most often through network access service providers - providers.
IV. Home Features of the Global Internet
Each user and server necessarily have a unique address. The message transmitted over the network is supplied with the addresses of the recipient and the sender and during the transmission is automatically divided by a network adapter on a piece of fixed-length, called packages. In this case, each package (also automatically) is supplied with the addresses of the sender and the recipient. On the receiving computer, packages are collected in a single message.
Each server or user computer in the network have addresses 3 levels:
- Local address - The address of the network adapter. Such addresses are prescribed by equipment manufacturers and are unique, because Their appointment is centrally. This address is used only within the local network.
- IP address - It is a four-scale sequence (4 single-byte integers without a sign of numbers) and consists of 2 parts:
The first 2 bytes characterize the network
Second 2 bytes - a specific node
Such an address is assigned to the network administrator regardless of the local address. If the network should work as an integral part of the Internet, then the network number (first 2 bytes) is assigned on the recommendation of the Special ICANN organization. Otherwise, the network number is selected by the administrator arbitrarily. The node number (second byte) is assigned to the network administrator (for example, 192.100.2.15). The node can enter several networks. In this case, it must have several IP addresses \u003d\u003e IP address characterizes not a separate computer, but one network connection. The message transmitted over the network is supplied with the IP addresses of the recipient and the sender.
- domain address (domain name) - the user is inconvenient to use IP addresses in the current operation \u003d\u003e Internal so-called. Domain system name system (DNS). This system provides user-friendly text names (identifiers), called domains, the corresponding IP addresses are hidden behind them. The user works with domain names, and the appropriate software using special DNS servers automatically converts them to the addresses that transmitted packets. The total domain name (DNS address) is a sequence of names, separated by a point. The first on the left is the name of a particular computer, then the domain name of the organization, region, etc., the last right is the name of the so-called. root domain. Root domain names indicate on the state (for example, RU - Russia, US - USA, KZ - Kazakhstan, etc.) or on belonging to the organization of a certain type (Com - Commercial, EDU - Educational, GOV - Government, MIL - Military, Net - Network, ORG - organization). Other similar root domains were identified later (arts - art, culture, firm - business, info - information, NOM - individual).
Computer names that have access to the Internet through a node (for example, a local network server) are separated from the subsequent part in the full name of the non-point, but sign @ ("fl"). For example, [Email Protected]
V.VIDA services in the Internet
The provision of services in the Internet is based on the client-server model. To connect a computer to the Internet, it is enough to have a telephone line, a provider having a gateway in the Internet and modem (mOdular- dem.tool) - a special adapter for connecting to a global network via telephone connection. Computer provider used by users to work in the Internet is called host. The most famous services provided by Internet server servers include:
- Email (e-mail) - is the process of transmitting messages between computers
- File transfer (FTP system) - Designed to send files from special FTP servers to any user, to get the file, specify the full server name and the full file specification
- View Resources (Gopher-system) - Provides search for files on GOPHER-servers in content (topic, keyword, phrase, etc.)
- Teleconference - Designed to conduct discussions and sharing news, allow you to read and send messages to open on different topics. The largest teleconference system is Usenet. (The user can "subscribe" to any of the existing topics, view the news, send messages). Another major teleconference system is IRC. (Internet Relay Chat) (allows you to communicate group members in real time (interactive mode), in which case the user sees constantly incoming information on the screen and at the same time can put their messages that immediately go to the screens of all other members of the group)
- World WWW web(World Wide Web) - is an attempt to combine in one information instrument the capabilities of the above-mentioned funds, adding the transfer of graphic images, sounds, video to them. The basis is the principle hypertext. (- The system of information facilities with cross-references, in documents contain references to other documents related in meaning). Previously applied only for text documents, currently a hypertext document is called hypermedia document. Objects on which links are created may be on remote computers. Hypermedia documents are created using a special HTML language (hypertext markup language) and stored on special servers (WWW server, Web server). Often such documents are called Web pages or Web sites. Relevant customers' programs are called browsers (From English. Browser) - search engine. Most modern browsers provide access not only to Web server pages, but also to other types of services. At the same time, referring to various resources, the so-called is used. URL (unified resource pointer). It has the following format: resource code: // Query specification.The resource code determines the type of service with which you want to work: HTTP - Working with Web servers, To view Web sites, FTP - FTP System, Gopher - Gopher-System, News - Communication with Use-Net, Mailto - Email and etc.
Units of measurement of the number and amount of information.
N. - Formula Hartley.
In the computer, the smallest unit of information is bit. Representation of each bit depends on the type of information medium. On paper, the bit is represented by a unit or zero, in the internal memory it corresponds to one of the two states of the cell element. On a magnetic surface, this is a point (magnetized or imperfected), and on the surface of the optical disk it corresponds to the presence or absence of deepening. Any information is encoded by a specific combination, i.e. binary signs.
The amount of information.
Since each bit can take one of two values \u200b\u200b(0 or 1), then the sequence of I - bits can take N \u003d 2 ͥ different values \u200b\u200b\u003d\u003e for any N - a valued alphabet (i.e. from n signs), the number of bits cat. It is required to represent any of these signs, is calculated by the formula: i \u003d log2 n. This value is taken as the number of information contained in the message consisting of one sign of the N-digit alphabet. Power - Number of signs in the alphabet. It follows from the Hartley formula that the amount of information contained in the message consisting of M-characters (M-discharge message), when each sign is equally taken from the alphabet with power n equals i \u003d M * log2 N.
For example:
In the word informatics 11 signs, i.e. M \u003d 11. If a 32-digit alphabet is used, then we obtain: i \u003d 11 * Log2 32 \u003d 11 * 5 \u003d 55.
Amount of information.
Unlike quantity, the amount of information recorded by binary signs in the computer's memory or on the outer carrier is calculated by the number of binary signs required for such a record. Usually, bytes consisting of 8 bits \u003d\u003e each byte can take 256 (2 ^ 8) of different values, while the smallest will be 00000000, and the largest 11111111. Bytes are combined into larger sets depending on the target. use (input, output and other). To measure the amount of memory, larger units (KB, MB and GB) are used. The transition from a smaller unit of measurement to the greater is carried out using the coefficient 2 ^ 10 \u003d 1024.
1 kb \u003d 1024 byte
1 mb \u003d 1024 kb
1 GB \u003d 1024 MB
To measure larger memory use Terabyte (TB) \u003d 1024 GB; and petabyte (PB) \u003d 1024 TB.
Any information is in the computer As a sequence of bytes, there is nothing in the bytes themselves, which allows them to be interpreted as numbers, text or other data. Anyway information is encoded in the form of sequences of zeros and units, i.e. positive integer binary numbers. Them interpretation (understanding) It depends on which program and what action with them makes in this and specific moment. If the program is assumed to work with numbers, the bytes are represented as the numbers to which arithmetic actions are used.
Number system.
Number - This is a sign denoting a certain amount of something.
Such signs are recorded on the basis of the rules that make up the number system. Numbers are recorded using special, distinct signs from each other, which are called numbers. There are various systems (inspirational and positional). In non-phase systems The meaning of each digit does not depend on its location.
For example:
In the Roman system V-five, L-Fifty, X-Ten. The disadvantage of such systems is the complexity of the number of numbers and the lack of standard rules.
In positional surgery The meaning of the number depends on the place of its location among the number, and the recording of the numbers and the rules for performing arithmetic actions with them are standardized and formalized. In such a number system number - This is a summary of the amount.
For example:
The number is a sequence of coefficients in the degrees of Number 10. The number 10 is called the base of the decimal number system. If you set another number as a base, we get another number system.
The positioning system is set to the value of the base and set numbers. The bases are equal to the number of numbers. The smallest zero, each next one more than the previous one. Any quantity can be represented as a number in various number systems and these views will be mutually uniquely appropriate to each other, denoting the same amount.
(10/10/2012)
For example, consider the representation of numbers in a 16-riche system. Then the base is 16. The numbers: the first ten digits (from 0 to 9) we can borrow from the 10-riche number system, the remaining six digits corresponding to the numeric values \u200b\u200bfrom 10 to 15 Denote by A, B, C, D, E, F. In this case, A \u003d digit 10, B \u003d number 11, etc. F \u003d Number 15. We are forced to make such a designation due to the fact that you can not be denoted by using other numbers.
Arithmetic actions in any number system is performed similarly to how this is done in a tenary system, you should only take into account the value of the base. For example: 15 + 14 \u003d 31 (octal number system). In the computer, all data are presented in a binary number system. For example: 
Four bits can be represented by 16 decimal numbers (from 0 to 15). As a brief record when viewing or changing binary data, a 16-riche number system is used. Programs providing the "direct" work of a person with data stored in a computer's memory, when interacting with a person, automatically convert a binary representation of data into 16-rich and back.
Any given, recorded in one pate seems to be two 16-richeful figures, the first of which corresponds to the first four bits, and the second - the second four bits. This is the reason for using a 16-riche system.
To present information in the memory of the computer (both numeric and non-numeric), a binary method of coding is used. Elementary memory cell of the computer has a length of 8 bits (bytes). Each byte has its own number (it is called the address). The largest sequence of the bit, which computer can process as a whole, is called a machine word. The length of the machine word depends on the discharge of the processor and may be equal to 16, 32 bits, etc. For encoding characters is enough single byte. In this case, you can present 256 characters (with decimal codes from 0 to 255). The IBM PC personal computer symbol set is most often the ASCII Code extension (American Standart Code for Information Interchange - Standard American Information Code). In some cases, when presenting in the memory of the computer, a mixed binary-decimal "Number system" is used, where it is necessary for the storage of each decimal sign, it is possible to store (4 bits) and decimal numbers from 0 to 9. A decimal format designed to store integers with 18 meaning numbers and occupies 10 bytes in memory (the senior of which is iconic), uses this particular option. Another way to represent integers is an additional code. The range of values \u200b\u200bdepends on the number of memory bits, allocated to store them. For example, the values \u200b\u200bof the Integer type (all names of the data types here and below are presented in the form in which they are taken in the TURBO PASCAL programming language, in other languages \u200b\u200bsuch data types are also there, but may have other names) lie in the range from -32768 ( -2 15) to 32767 (2 15 - 1), and 2 bytes are given to storage; type LongLNT - in the range from -2 31 to 2 31 - 1 and placed in 4 bytes; type Word - in the range from 0 to 65535 (2 16 - 1) (used 2 bytes), etc. As can be seen from examples, data can be interpreted as numbers with signs and without signs. In the case of representing the value with the sign, the leftmost (senior) discharge indicates a positive number if it contains zero, and on a negative, if the unit. In general, the discharges are numbered on the right, starting with 0. The following is the numbering of bits in a two-byte machine word. 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Additional code of a positive number coincides with its direct code. The direct code of an integer can be obtained as follows: the number is translated into a binary number system, and then its binary recording on the left is complemented by such a number of insignificant zeros, how much does the data type require that the number belongs to. For example, if the number 37 (10) \u003d 100101 (2) is declined by the type of Integer, then its direct code will be 0000000000100101, and if the value of type LongLNT, then its direct code will be. For a more compact record, hexadecimal code is used more often. The obtained codes can be rewritten according to 0025 (16) and 00000025 (16). Additional code of a whole negative number can be obtained according to the following algorithm: 1) Record the direct code of the module of the number; 2) invert it (replace units with zeros, zeros - units); 3) add to the inverse code unit. For example, we write an additional number code (-37), interpreting it as a value of type LongLNT: 1) the direct number of the number 37 is; 2) inverse code; 3) Additional code or FFFFFFFDB (16). Upon receipt of the number according to its additional code, it is primarily necessary to determine its sign. If the number turns out to be positive, then simply translate its code into a decimal number system. In the case of a negative number, the following algorithm must be performed: 1) subtract from the code number 1; 2) invert code; 3) Translate into a decimal number system. The resulting number is written with a minus sign. Examples. We write the numbers corresponding to additional codes: a) 00000000010111. Since zero is recorded in the senior discharge, the result will be positive. This is the code number 23; b) 111111111000000. A negative number is recorded here. We perform algorithm: 1) 111111111000000 (2) - 1 (2) \u003d 11111111111111 (2); 2) 0000000001000000; 3) 1000000 (2) \u003d 64 (10). Answer: -64. A slightly different method is used to represent real numbers in the memory of the personal computer. Consider the presentation of the floating point values. Any valid number can be written in the standard form M10 P, where 1
The IBM PC personal computer allows you to work with the following valuable types (the range of values \u200b\u200bis indicated by absolute value): Let us show the transformation of the actual number to represent it in the computer's memory using the example of the value of the Double type. As can be seen from the table, the value is the type takes 8 bytes in memory. The figure shows how the Mantissa fields and order are presented here: it can be noted that the senior bit, allotted under the Mantissa, has a number 51, i.e. Mantissa takes the younger 52 bits. The trait indicates a binary point here. Before the comma should be a bit of the whole part of the mantissa, but since it is always equal to 1, this bit is not required and there is no corresponding discharge in memory (but it is meant). The value of the order to simplify the calculations and the comparison of the actual numbers is stored in the form of a displaced number, i.e. To the correct value of the order before recording it in memory is added offset. The displacement is chosen so that the minimum value of the order corresponds to zero. For example, for the type Double, the order occupies 11 bits and has a range of 2 ~ 1023 to 2 1023, so the offset is equal to Yu23 (10) \u003d 1111111111 (2). Finally, the bit with number 63 indicates the number of numbers. Thus, the following algorithm follows from the above to obtain a valid number in memory of the computer: 1) to translate the module of a given number into a binary number system; 2) normalize binary number, i.e. Write in the form of M-2 P, where the Mantissa (its integer part is 1 (2)) and p - order recorded in a decimal number system; 3) add to the order offset and translate the displaced order into the binary number system; 4) Given the sign of a given number (0 - positive; 1 - negative), write it down in the memory of the computer. Example. Write the number code -312,3125. 1) The binary entry of the module of this number has a view of 100111000,0101. 2) We have 100111000,0101 \u003d 1.001110000101 2 8. 3) We obtain a displaced order of 8 + 1023 \u003d 1031. Next, we have Y31 (10) \u003d \u003d 10000000111 (2). . 4) Finally
1) First of all, we notice that this is the code of a positive number, because in discharge with the number 63, zero is recorded. We obtain the order of this number: 011111111110 (2) \u003d 1022 (10); 1022 - 1023 \u003d -1. 2) The number has the form 1.1100011-2 "1 or 0.11100011. 3) We obtain 0.88671875 by the translation into the decimal number system.
