Local area network
Metropolitan area network (also called local area network)
WAM wide area network (internet
According to the network topology:
First, the star structure.
B, hierarchical structure or tree structure.
C, bus-shaped structure.
D, ring structure.
E. Irregular shape of point-to-point partial connection.
F. Point-to-point full connection structure.
Others are classified according to different angles: wide area network WAN, local area network LAN and metropolitan area network MAN according to distance.
According to the communication medium, it is divided into wired network and wireless network; According to the communication mode, it is divided into point-to-point mode and broadcast mode; According to the speed, it is divided into low, medium and high speed;
According to the scope of use, it is divided into public network and private network; According to the network control mode, it is divided into centralized and distributed.
12. At present, the common network transmission media are twisted pair, coaxial cable and optical fiber.
13. The English word for Multimedia is multimedia, which consists of two parts: media and multi. Generally understood as the synthesis of various media.
Multimedia technology is not a simple combination of various information media. It is an information technology that combines information in the form of words, graphics, images, animations and sounds, and is comprehensively processed and controlled by a computer, which can support a series of interactive operations. The development of multimedia technology has changed the application field of computers, which has changed computers from special products in offices and laboratories to ordinary tools in the information society, and has been widely used in industrial production management, school education, public information consultation, commercial advertisements, military command and training, and even family life and entertainment.
Multimedia technology has the following main features:
(1) integration can acquire, store, organize and synthesize information through multiple channels.
(2) Controlled multimedia technology is a computer-centered comprehensive processing and control of multimedia information, which is displayed in various media forms according to people's requirements and acts on people's various senses at the same time.
(3) Interactivity Interaction is one of the main characteristics that distinguish multimedia applications from traditional information exchange media. Traditional information communication media can only spread information in one direction and passively, while multimedia technology can realize people's active choice and control of information.
(4) The nonlinear characteristics of nonlinear multimedia technology will change people's traditional sequential reading and writing mode. In the past, people mostly used the framework of chapters, sections and pages to acquire knowledge step by step, while multimedia technology will present the content to readers in a more flexible way with the help of hypertext links.
(5) Real-time when the user issues an operation command, the corresponding multimedia information can be controlled in real time.
(6) Convenience of information use Users can use information according to their own needs, interests, task requirements, preferences and cognitive characteristics, and can take any form of information such as pictures, words and sounds.
(7) Dynamic information structure "Multimedia is a book that can never be read". Users can reorganize information, add, delete or modify nodes and re-establish links according to their own purposes and cognitive characteristics.
14. An ordinary multimedia computer consists of a host, a monitor, a keyboard, a mouse and a speaker. There are printers and scanners, which are important input and output devices of computers.
15. The principle of MID music format is that the source file only provides one or several strings of music score information flow, and a music notation corresponds to a standard sound in your computer sound card. When the player reads midi, it is a task to extract, process and synthesize midi from the sound card. Therefore, midi can be compressed to a very small size (only a few tens to a hundred K for a five-minute tune), but you must not think that its sound quality is not good. On the contrary, because it is the standard sound of the sound card, the sound quality is just intact! ! This is only superior to MP3 in source sound quality.
However, the biggest disadvantage of Midi is that it can't put complex and changeable vocals into the music score, and it can't add transformation effects at will, just like the piano can't play vocals.
16. Bitmap image
Bitmap images (technically called raster images) use color grids (that is, pixels) to represent images. Each pixel has its own specific position and color value. For example, a bicycle tire in a bitmap image is patched together by pixels in this position. When working with bitmap images, you are editing pixels, not objects or shapes.
Bitmap images are the most commonly used electronic media for continuous tone images (such as photos or digital paintings) because they can represent the subtle levels of shadows and colors. Bitmap images are related to resolution, that is, they contain a fixed number of pixels. Therefore, if you scale them on the screen or print them at a lower resolution than when they were created, the details will be lost and they will appear jagged.
vector graphics
Vector graphics consist of straight lines and curves defined by mathematical objects called vectors. Vector describes an image according to its geometric features.
Vector graphics are independent of resolution, that is, you can scale them to any size and print them at any resolution without losing details or reducing clarity.
Non-bitmap images contain vector images, but are not specific.
17. Lossy and lossless compression. 1. Lossy compression Lossy compression can reduce the space occupied by images in memory and disk. When you watch images on the screen, you won't find that it has a great adverse effect on the appearance of images. Because human eyes are sensitive to light, the effect of light on scenery is more important than color, which is the basic basis of lossy compression technology. The characteristic of lossy compression is to keep the gradual change of color in the image and delete the sudden change of color in the image. A large number of experiments in biology have proved that the human brain will use the closest color to fill the lost color. For example, for a white cloud on a blue sky background, the method of lossy compression is to delete some color parts at the edge of the scene in the image. When looking at this picture on the screen, the brain will fill in the missing color part with the color seen on the spot. Using lossy compression technology, some data is intentionally deleted, and the deleted data is not recovered. Undeniably, using lossy compression technology can greatly compress the data of files, but it will affect the image quality. If the lossy compressed image is only displayed on the screen, it may have little effect on the image quality, at least for the recognition of human eyes. However, if the image processed by lossy compression technology is printed by a high-resolution printer, the image quality will be obviously damaged. 2. Lossless compression The basic principle of lossless compression is that the same color information only needs to be saved once. Software that compresses an image will first determine which areas in the image are the same and which are different. Images containing duplicate data (such as blue sky) can be compressed, and only the starting point and ending point of blue sky need to be recorded. However, there may be shades of blue, and the sky may sometimes be blocked by trees, peaks or other objects, which need to be recorded separately. In essence, lossless compression can delete some duplicate data and greatly reduce the image size to be saved on disk. However, the lossless compression method can not reduce the memory occupation of the image, because when reading the image from the disk, the software will fill the missing pixels with appropriate color information. If we want to reduce the memory occupied by images, we must use lossy compression method. The advantage of lossless compression method is that it can better preserve the image quality, but the compression rate of this method is relatively low. However, if the image needs to be printed by a high-resolution printer, it is best to use lossless compression. Almost all image files use their simplified format names as file extensions. From the extension, we can know what format this image is stored in, what software should be used to read/write, and so on.
18.mov. asf。 3gp。
19. Database management system is a large-scale software for manipulating and managing databases, which is used to establish, use and maintain databases, or dbms for short. It manages and controls the database in a unified way to ensure the security and integrity of the database. Users access the data in the database through dbms, and database administrators also maintain the database through dbms. It provides a variety of functions, enabling multiple applications and users to establish, modify and query databases in different ways at the same time or at different times. It enables users to define and manipulate data conveniently, maintain the security and integrity of data, and carry out concurrent control and database recovery under multi-users.
Data is a symbolic representation of objective things, and it is the original material used to represent objective things, such as graphic symbols, numbers, letters and so on. In other words, data are facts and concepts obtained through physical observation, and they are descriptions of places, events, other objects or concepts in the real world.
A database is a warehouse. According to its definition, content and structure, it stores data according to a certain pattern.
Database system is a practical software system for storing, maintaining and applying data, and it is a collection of storage media, processing objects and management systems. It usually consists of software, database and data administrator. Its software mainly includes operating system, various host languages, utilities and database management system. The database is managed by the database management system, and the insertion, modification and retrieval of data should be carried out through the database management system. The data administrator is responsible for creating, monitoring and maintaining the entire database so that anyone who has access to the data can use the data effectively. Database administrators are generally people with higher professional level and deeper qualifications.
A computer program is a set of instructions that a computer can recognize and run.
A program is a prescribed way to perform an activity or process, and consists of a sequence that tells a computer how to complete a specific task. Because today's computers can't understand human natural language and can't write computer programs in natural language.
2 1. compilation: converting a program into code that a computer can recognize and execute. Or generate an executable file.
Note: add your own comments to the program to make it easy for people to understand.
22. Computer viruses are clearly defined in the Regulations on the Security Protection of Computer Information Systems in People's Republic of China (PRC). A virus refers to "a set of computer instructions or program codes compiled or inserted in a computer program that destroy computer functions or data, affect the use of the computer and can replicate itself".
Generally, a virus that spreads widely will allow users to run the virus automatically when they restart their computers, thus infecting computers for a long time and expanding their virus infection ability.
Usually, the first thing that viruses infect computers is to kill their natural enemies-security software, such as Kaspersky, 360 security guards, NOD32 and so on. In this way, we can't use antivirus software to deal with computers that have been infected with viruses. Then let me talk about the method of manual antivirus.
To solve the virus, you can first solve the problem of self-startup after computer restart.
Usually viruses start like this.
Direct self-startup, 1. Boot sector 2. Driver 3. Service 4. Registry.
Indirect self-startup: impression hijacking, autorun.inf file, HOOK, infected file.
23. Computer viruses can be divided into system boot virus, executable file virus, macro virus, mixed virus, Trojan horse virus and network language virus.
24. At present, WAN has been applied to all levels of local tax system in the province. Wide area network has a wide coverage, a large number of users and a high degree of resource enjoyment. The threats and attacks it faces are complex, which can be summarized as physical security, operating system security, application security and network protocol security.
(1) Physical security. Network security must first ensure the physical security of information on the network. Physical security refers to the information security protection of storage and transmission at the level of physical media. At present, common unsafe factors (security threats or security risks) include three categories:
1. Natural disasters (such as lightning, earthquake, fire, flood, etc. ), physical damage (such as hard disk damage, expiration of equipment service life, external force damage, etc. ), equipment failure (such as power failure, electromagnetic interference, etc. ), there are accidents.
2. Electromagnetic leakage (such as intercepting the running process of microcomputer).
3. Operation errors (such as deleting files, formatting hard disk, deleting lines, etc.). ) and unexpected omissions (such as power failure, crash and other system crashes).
25. The function of the firewall
The firewall scans the network traffic flowing through it, which can filter out some attacks before they are executed on the target computer. Firewalls can also close unused ports. In addition, it can also prohibit outgoing communication on specific ports and block Trojans. Finally, it can prohibit access from special sites, thus preventing all communication from unknown intruders.
Firewall is the barrier of network security;
Firewalls (as blocking points and control points) can greatly improve the security of internal networks and reduce risks by filtering unsafe services. Because only carefully selected application protocols can pass through the firewall, the network environment becomes more secure. For example, a firewall can prohibit the well-known insecure NFS protocols from entering or leaving the protected network, so it is impossible for external attackers to use these fragile protocols to attack the internal network. Firewalls can also protect the network from route-based attacks, such as source routing attacks in IP options and redirection paths in ICMP redirection. The firewall should be able to reject all messages of the above attack types and notify the firewall administrator.
Firewall can strengthen the network security strategy:
Through the firewall-centered security scheme configuration, all security software (such as password, encryption, authentication, audit, etc. ) can be configured on the firewall. Compared with distributing network security problems to various hosts, centralized security management of firewall is more economical. For example, in network access, authentication systems such as one-time password system can be centralized on the firewall, rather than scattered on each host.
Monitor and audit network access and access:
If all the accesses go through the firewall, the firewall can record these accesses and make a log record, and at the same time, it can provide statistical data of network usage. When suspicious behavior occurs, the firewall can issue appropriate alarms and provide detailed information about whether the network is being monitored or attacked. In addition, it is also very important to collect the usage and misuse of a network. The first reason is to make clear whether the firewall can resist the detection and attack of attackers and whether the control of the firewall is sufficient. Network usage statistics are also very important for network demand analysis and threat analysis.
Prevent internal information leakage:
By dividing the internal network with a firewall, the key network segments of the internal network can be isolated, thus limiting the impact of local key or sensitive network security issues on the global network. In addition, privacy is a matter of great concern to the internal network. The inconspicuous details in an internal network may contain security clues, arouse the interest of external attackers, and even expose some security loopholes in the internal network. Using firewalls can hide services that reveal internal details, such as Finger and DNS. Finger displays the registered name, real name, last login time and shell type of all users of the host. But the information displayed by the finger is very easy for the attacker to know. Attackers can know how often a system is used, whether there are users online, whether the system attracts attention when it is attacked, and so on. The firewall can also block DNS information about the internal network, so that the domain name and IP address of the host will not be known to the outside world.
In addition to the security function, the firewall also supports VPN (Virtual Private Network), which is an enterprise internal network technology system with Internet service characteristics.
The English name of FireWall is "firewall", which is the most important network protection equipment at present. From a professional point of view, a firewall is a set of components located between two (or more) networks to realize access control between networks.
Firewalls usually appear in the network as two icons, as shown in the following figure. The icon on the left is very vivid, really like a wall. The icon on the right is visualized from the filtering mechanism of firewall, and there is a diode icon in the icon. We know that the diode is unidirectional, which vividly shows that the firewall is unidirectional. This seems to be somewhat contradictory to the current firewall filtering mechanism, but it fully reflects the original design idea of the firewall and also reflects the current firewall filtering mechanism to a certain extent. Because the original design idea of fire prevention is to always trust the internal network and never trust the external network, the original firewall only filters the incoming communication from the outside and does not restrict the communication sent by the users in the internal network. Of course, the current firewall has changed the filtering mechanism, not only filtering the communication connections sent by the external network, but also filtering the connection requests and data packets sent by some users in the internal network. However, the firewall still only passes the communication that conforms to the security policy, which can also be said to be "one-way conduction".
It's hard to find .....