Basic knowledge of computer

Development and classification of computers

1946 The first computer in the world that can be controlled by a program developed by the University of Pennsylvania in the United States is called an electronic numerical integral calculator, or ENIAC for short. The word length of this computer is 12 bits, the main memory is only 17K, the operation speed is 5000 addition operations per second, * * * uses 18800 tubes, 1500 relays, the area is 150m2, the weight is 30t, and the power consumption is 650. Today, it seems that this computer is expensive and heavy, with low operation speed, short words and high power consumption. However, it is the pioneer of today's electronic computers with different sizes and modes, which laid the foundation for the development of computer technology. If ENIAC is called the first generation electronic computer, it has developed to the fourth generation.

The first generation (1946- 1958) electronic tube digital computer

Electronic tubes are used as logic components of computers, magnetic drums and cores are used as main memory, and tape software based on machine language has been used as external memory, and then it has gradually developed into assembly language. Mainly used for scientific calculation.

The second generation (1958 ——1964) transistor digital computer

The logic element of computer adopts transistor, the main memory adopts magnetic core, and the external memory has begun to use disk; Software began to develop greatly, and various high-level languages and compilers appeared. At this time, the speed of the computer is obviously improved, the power consumption is reduced and the service life is improved. Computers have been developed for various transaction processing and started to be used in industrial control.

The third generation (1964- 197 1 year) integrated circuit computer.

The logic elements of the computer adopt small-scale and medium-scale integrated circuits, which are called SSI and MSI. The software develops rapidly, with a time-sharing operating system, and its application scope is expanding day by day.

The fourth generation (197 1 year later) large-scale and very large-scale integrated circuit computers.

The logic elements of the computer are large-scale integrated circuits (LSI), and an integrated circuit with 1000 to 20000 transistors can be integrated on a silicon chip. However, VLSI currently integrates as many as 50 million transistors.

At present, computer technology is developing rapidly, the development direction is mainly towards large-scale and giant development, and the other is towards miniaturization and miniaturization.

1. Large supercomputer

In order to meet the needs of the development of modern science and technology, computers are required to improve the operation speed and increase the main storage capacity, so large and giant computers appear. For example, Cray- 1, Cray-2 and Cray-3 supercomputers produced by Cray Company in the United States are very famous. China's Yinhe-1 is a parallel supercomputer with10 billion times per second. Supercomputers symbolize the scientific and technological strength of a country. At present, only a few countries have the ability to produce them. Mainframe is fast and large in capacity, which solves the real-time complex mathematical problems that could not be calculated in the past, but the equipment is huge and expensive.

2. Minicomputers and microcomputers

The appearance, popularization and application of small and microcomputer meet the requirements of small size, low cost and high reliability in aerospace and missile technology and general applications.

Central processing unit (CPU) is the heart of a microcomputer, which is integrated on a small chip called MPU (Microprocessor) to distinguish the CPUs of large, medium and small computers. In addition to MPU, microcomputer also has main memory and input/output interface circuit made of large-scale integrated circuit, which are connected by bus structure. If equipped with corresponding peripheral equipment such as CRT, keyboard, printer, etc., it becomes a microcomputer system. At present, the functions of microcomputers are already very powerful. For example, the integration of Pentium 4 CPU has reached more than 40 million transistors, and the clock frequency is as high as 3000MHz. Microcomputer has become an extremely important branch of modern computer field because of its simple structure, strong versatility and low price, and its development has advanced by leaps and bounds.

Second, the purpose of the computer

Our door is now in the age of science and technology, and the application of computers is everywhere. This chapter can help you understand the application of computers in different fields.

3. 1 education

Computer as a learning tool

Computer-aided learning is the use of computers as learning tools. At present, many computer-aided learning softwares help students learn different subjects through words, images, sounds, images and animations. At the same time, you can test what you have learned and get the test results immediately.

A large number of learning resources can also be found online, and students can also learn some extracurricular knowledge by themselves.

Computer as a teaching tool

Computers are also good teaching AIDS. By using computers, teachers can show the teaching content more clearly, explain some concepts that are difficult to explain and show some experiments that are difficult to carry out in practice with more interesting multimedia (images, videos, animations, sounds and words) effects, making learning more interesting.

Computer as a school management tool

With the help of computers, school management will be more efficient. Schools can use computers to store and process a large amount of data, such as each student's personal records, class lists, examination results of various subjects, library books and materials, and so on.

3.2 entertainment

computer game

Computer games can be divided into adventure games, action games, educational games, intellectual games, simulation games and strategy games. And most of them contain a lot of visual and auditory effects. Good computer games can stimulate the imagination of game participants and provide them with the fun of challenges and the joy of success.

Film and television production

Using computers, we can make special sound and visual effects in movies or TV programs; At present, many sci-fi or action movies are made with the help of computer technology, which brings us new forms of entertainment.

Interactive TV

Now, we only need to connect a control box, and we can sit at home and enjoy the VOD service. You just need to choose the movie you like to watch, and the computer system will send the video over the telephone line for you to watch on the TV at home.

3.3 Household appliances

home appliances

Control many computer programs, such as video recorder, washing machine, automatic temperature control of refrigerator air conditioner, microwave oven heating program.

Smart home

The so-called smart home means that all electrical appliances in the home are controlled by computers and switched on and off on time through programming, voice control or telephone control.

3.4 transportation

Traffic monitoring

Traffic lights, electronic road tolls and land, sea and air traffic monitoring systems are all controlled by computers.

distribute

The deployment of railway systems, cars, ships and planes are all controlled by computers.

ticket business

Ticket vending machines, Octopus and other ticketing systems are all controlled by computers.

3.5 communication

telephone

The telephone system in most countries has been computerized, which further improves the sound quality, lines and working environment of telephone buildings.

e-mail

E-mail software allows people to send and receive information on computer networks. This is a fast, economical and convenient way of information transmission.

real-time communication

Conduct online games, chat rooms, ICQ, VoIP, video conferencing, etc. Video conferencing allows people to have face-to-face conversations with others through computer networks.

3.6 commerce

Financial industry

The operations and records of branches of financial institutions are all connected by computers. You can use the ATM to deposit, withdraw or transfer money. Now you can connect to the bank's computer system by telephone, TV or computer, so

1. Query the balance of the extended account;

2. Inflation;

3. Get financial information.

Sales industry

Department stores and supermarkets use computerized point-of-sale terminals to read commodity data (names and prices), print invoices, control inventory, and connect systems with various point-of-sale terminals to control inventory levels and order quantities.

service industry

Many service industries have begun to use computers to improve efficiency. Hotels can use computers and the Internet to book rooms, restaurants can use computers to place orders and settle accounts, travel agencies can use computers to book air tickets and hotels for customers, and shopping companies can use the Internet for shopping services.

3.7 Office applications

Office automation is to use computerized equipment to handle office work. General automation offices usually use the following types of application software:

word processor

Word processing software can be used to create, edit, proofread, format and print documents.

trial balance

Spreadsheet software can calculate, analyze and display data.

database

Database software can store, organize and update a large amount of data.

Briefing software

Briefing software can display reports or introduce data to participants in a meeting.

Three, the computer has the following characteristics:

Fast calculation ability, high enough calculation accuracy and super memory ability.

Four, the basic composition of the computer system

potato

Central processor controller

Host internal memory

External hardware memory

Peripheral input device

Microcomputer output equipment

System operating system

System software service software

Software compilation or interpretation system

Information management software

Application software aided design software

word processor

Graphic software

All kinds of packaging

Five, the composition of the hardware system and the main functions of each component

The computer hardware system consists of five parts: arithmetic unit, controller, memory, input device and output device.

1. Operator

The arithmetic unit is an "information processing factory". The operation and processing of data are carried out in the arithmetic unit. The "operation" here includes not only basic arithmetic operations such as addition, subtraction, multiplication and division, but also some basic logical operations.

2. Controller

The controller is the command center of the whole computer. It takes out the control information in the program, and sends out the operation control signal as required after analysis, so that all parts can work in harmony.

Step 3 remember

A place where programs and data are stored, and memory is provided for relevant parts of the computer according to commands.

The main technical parameters of 1) memory: storage capacity, access speed and bit price (that is, the price of a binary bit).

2) Memory capacity: indicates the computer's ability to store information, in bytes. 1 byte is 8 bits. Because the capacity of internal memory is generally relatively large, especially the capacity of external memory increases very quickly, the company name is constantly expanded by a multiple of 2 10 (1024). The relationship between these units is as follows: (thousands, trillion, and Kyrgyzstan), so the unit names are continuously expanded in multiples of 2 10 (1024). The relationship between these units is as follows: (thousands

1 byte = 8-bit lKB = l024 bytes

lMB = 1024 kb lGB = 1024 MB

3) Composition of storage system:

The storage system includes a main memory (internal memory), an auxiliary memory (external memory) and a cache. The three components form a hierarchical structure according to the advantages and disadvantages of access speed, storage capacity and bit price, so as to improve the increasingly high speed requirements of CPU and better solve the contradiction of the three technical parameters. The level of data exchange between them is shown in Figure 2.

4) Main memory

Stores the programs, data and intermediate information currently involved in the operation. It exchanges information with the arithmetic unit and the controller.

Features: small storage capacity, fast access speed and reasonable bit price. Stored information cannot be kept for a long time (it will be lost when power is cut off)

4. Input devices.

The most common are keyboards and mice. We can transmit some basic information to the computer through the input of the keyboard {Figure 1} and the operation of the mouse {Figure 2}, as well as the hard disk and floppy disk in the computer, and transmit the information stored in the disk in advance to the computer through the operation. There are also scanners (Figure 3), digital cameras (Figure 4) and digital cameras (Figure 5), which can transmit some photos and videos to the computer. The ear pulse in our computer {Figure 6} can also be used as an input device, combined with the software operation in the computer, to transmit sound to the computer. There is also an electronic touch screen in the input device. In the post office, we can operate directly on the touch screen and query the postal codes of all parts of the country.

5. Output devices

Is a component of human-computer interaction, used for data output. It expresses all kinds of calculation result data or information in the form of numbers, characters, images and sounds. Common ones are display {Figure 7}, printer {Figure 8}, plotter, image output system, voice output system, magnetic recording equipment, etc.

Basic concepts of data storage of intransitive verbs

Data storage is a temporary file or information that needs to be found during data stream processing. Data is recorded in a certain format on the internal or external storage media of the computer. Data storage should be named, and the composition meaning of information characteristics should be reflected. Data flow reflects the flow of data in the system and shows the characteristics of dynamic data; Data storage reflects the static data in the system and shows the characteristics of static data.

Commonly used storage media are disk and tape. The organization of data storage varies with storage media. On magnetic tape, data is only accessed in the form of sequential files; On the disk, sequential access or direct access can be used according to the use requirements. The data storage mode is closely related to the data file organization, and its key lies in establishing the corresponding relationship between the logical and physical order of records and determining the storage address to improve the data access speed.

(There is a sequel below)

Seven, the basic knowledge of software

Operating system is one of the most important system software, which is mainly used to manage computer hardware resources and provide us with an environment for controlling and operating computers. Windows98 is a typical operating system software. We operate and control our computer through the desktop, menus, control panels and other parts.

Common operating systems include DOS, Windows3.x, UNIX, Mac OS, etc.

The operating system is the supreme commander of the computer system, and all software depends on the instructions of the operating system. Hardware and software are inseparable from the support of the operating system. Generally speaking, the operating system undertakes the following important missions:

Manage various hardware resources of computer system, such as CPU, memory space, disk space, input/output devices, etc.

Manage all kinds of software resources in the computer system.

Responsible for coordinating the hardware, software and the relationship between software and hardware of the computer system, and reasonably organizing the workflow of the computer.

As a bridge to exchange information between computers and users. When the operating system is installed on the computer, people no longer directly operate the hardware of the computer, but use the commands and services provided by the operating system to deal with various hardware and software of the computer. It can be said that the operating system establishes the interface and channel between the user and the computer.

In short, without the management and intermediary role of the operating system, computers are worthless to ordinary people. DOS, OS/2, UNIX, Windows and Mac OS are all operating systems that can be applied to microcomputers, among which DOS and Windows are the most commonly used operating systems for microcomputers.

See the book for the relationship between people, computers and operating systems.

Application software is a variety of application programs compiled for a practical application or solving a problem. These programs are very practical and can be used to solve specific problems in an application field. Such as transaction management software, word processing software, auxiliary teaching software, auxiliary design software, various game software and so on.

In addition, the application software must be connected to the operating system. In other words, an application can only run in one operating system.

Software use ethics: use legal software, use genuine software; Do not illegally copy software, and do not use pirated software.

3. Computer virus and its prevention and control

Computer virus is not a common biological virus or bacterial virus, but also a computer program.

Computer viruses are contagious, diffuse, hidden and destructive. See the book for detailed introduction and examples.

Preventive measures for computer viruses are:

Don't use floppy disks and CDs of unknown origin, and you are not sure whether they contain viruses.

If you must use foreign floppy disks, you should first check the virus with anti-virus software to make sure you don't carry the virus before you can use it.

Do not illegally copy software, and do not use pirated software.

Write-protect the system disk, program disk and floppy disk of important data, and make backup.

Regularly use anti-virus software to carry out anti-virus detection on computers, and find and remove viruses in time.

Commonly used anti-virus software to remove computer viruses are: KILL, KV300, Rising anti-virus software, Norton and so on.

The most thorough way to understand the virus is to repartition and format the infected disk. Formatting the disk will delete all programs and data on the disk, including the operating system, so the virus will also be deleted as a program. However, due to the serious consequences of hard disk formatting, and it is difficult to install the operating system after formatting, so don't format the hard disk easily, and ask professionals to operate it.

Eight, numerical representation in the computer.

Numerical values are expressed in the form of machine numbers in computers. Computers can only recognize 0 and 1 and use binary, while people use decimal in their daily lives. "As Aristotle pointed out a long time ago, the widespread adoption of decimal today is only the result of anatomical facts, that is, most of us are born with 10 fingers.

There are positive numbers and negative numbers, so the computer uses the most significant bit of a number to store symbols (0 is positive, 1 is negative). This is the original code of the machine number. Assuming that the number of bits that the machine can handle is 8, that is, the word length is 1 byte, the range that the original code can represent this number is as follows

(- 127 ~-0+0 ~ 127) * * * 256.

With numerical representation, it is possible to perform arithmetic operations on logarithms. However, it was soon found that the result was correct when the original code with signed bits was used for multiplication and division, but there were problems when adding and subtracting, as follows: Suppose the word length was 8 bits.

( 1 ) 10- ( 1 ) 10 = ( 1 ) 10 + ( - 1 ) 10 = ( 0 ) 10

Executing the original code operation: (00000001) original+(1000001) original = (10000010) original = (-2) is obviously incorrect.

Because there is no problem in adding two positive numbers, it is found that the problem occurs in negative numbers with signed bits.

Invert the remaining bits bit by bit except the sign bit to generate the inverse code (for positive numbers, the inverse code is the same as the original code). The value space of the inverse code is the same as that of the original code, and corresponds to it one by one. The following is the subtraction of the inverse code:

( 1 ) 10 - ( 1 ) 10= ( 1 ) 10+ ( - 1 ) 10= ( 0 ) 10

Perform the operation of anti-code: (000000 1) anti+(111165438) anti = (11)

( 1 ) 10 - ( 2) 10 = ( 1 ) 10 + ( -2 ) 10 = ( - 1 ) 10

To perform the anti-code operation: (0000001) anti+(111) anti = (11668.

The problem occurred in (+0) and (-0). In people's concept of calculation, zero is neither positive nor negative. Indians first used zero as a symbol and put it into operation. Indian mathematics and decimal counting including zero made great contributions to human civilization. ) 。

So the concept of complement is introduced. The complement of a negative number is the complement plus one, and so is the complement of a positive number. In the complement, (-128) is used instead of (-0), so the expression range of the complement is:

(- 128~0~ 127)***256.

Note: (-128) has no corresponding original code and anti-code. (-128) = (100000) The addition and subtraction operations of complement are as follows:

( 1 ) 10- ( 1 ) 10= ( 1 ) 10 + ( - 1 ) 10 = ( 0 ) 10

(0000000 1) complement+(11111) complement = (0000000).

( 1 ) 10- ( 2) 10= ( 1 ) 10 + ( -2 ) 10 = ( - 1 ) 10

(0000000 1) complement+(1111/kloc-0) complement = (1/kloc-0)

So the purpose of supplementary design is:

(1) The sign bit can participate in the operation together with the effective value part, which simplifies the operation rules.

⑵ Convert subtraction operation into addition operation, which further simplifies the circuit design of calculator in computer.

These transformations are all carried out at the bottom of the computer, while the original code is used in other high-level languages such as assembly and C. After reading the above contents, everyone should have a new understanding of the original code, complement and complement!

Nine, common external equipment

Keyboard, mouse, monitor, printer, stereo, earphone, scanner.

X. What is a CPU?

CPU is the abbreviation of "Central Processing Unit/ Central Processing Unit" in English. Generally speaking, CPU consists of logic operation unit, control unit and storage unit. There are some registers in the logic operation and control unit, which are used for temporary storage of data during CPU processing. In fact, when we buy a CPU, we don't need to know its structure, just know its performance. The main performance indicators of CPU are: the main frequency is the clock speed of CPU. This is our greatest concern. When we say 233,300, etc. We are serious. Generally speaking, the higher the main frequency, the faster the CPU and the higher the whole machine. Clock frequency is the external clock frequency of CPU, which is provided by the computer motherboard. It used to be 66MHz, and some motherboards supported 75 MHz and 83MHz respectively. At present, Intel's latest chipset BX uses the clock frequency of 100MHz. In addition, some non-Intel chipsets, such as MVP3 and MVP4 of VIA, also began to support the external frequency of 100MHz. The BX motherboards of elite companies can even support the external frequency of 133MHz, which is the first choice for overclockers. Internal cache (L 1 Cache): a cache encapsulated in a CPU chip, which is used to temporarily store some instructions and data during CPU operation. The access speed is consistent with the main frequency of CPU, and the capacity unit of L 1 cache is generally KB. The larger the L 1 cache, the fewer times the CPU exchanges data with L2 cache and memory with slow access speed, which can improve the running speed compared with computers. L2 cache: cache outside the CPU. L2 of Pentium Pro processor runs at the same frequency as CPU, but it is expensive, so the running frequency of Pentium II is half that of CPU, and its capacity is 5 12K. In order to reduce the cost, Inter Company produced an L2-free CPU named Celeron, which has good performance and is very suitable for overclocking. MMX technology is the abbreviation of "Multimedia Extended Instruction Set". MMX is a new technology adopted by Intel in 1996, which is used to enhance the application of Pentium CPU in audio, video, graphics and communication. Adding 57 MMX instructions to the CPU, in addition to adding MMX instructions to the instruction set, the L 1 cache in the CPU chip is increased from the original 16KB to 32KB( 16K instruction+16K data), so the multimedia processing capacity of MMX CPU is improved by 60 compared with that of ordinary CPU. At present, CPU basically has MMX technology, besides P55C and Pentium II CPU, there are K6, K6 3D, MII and so on. Manufacturing technology: Now the manufacturing technology of CPU is 0.35 micron, the latest PII can reach 0.28 micron, and the future CPU manufacturing technology can reach 0. 18 micron.

XI。 The concept of memory

In the structure of a computer, there is a very important part, that is, memory. Memory is a component used to store programs and data. For a computer, only with memory can it have memory function and can it work normally. There are many kinds of memories, which can be divided into main memory and auxiliary memory according to their uses. Main memory is also called memory (referred to as memory, Hong Kong and Taiwan called memory).

Memory is the place where programs and data are stored. For example, when we use WPS to process documents, when you enter characters on the keyboard, it will be stored in memory. When you choose to save, the data in the memory will be stored on the hard (magnetic) disk. Before we know it further, we should also know its physical concept.

Memory generally uses semiconductor memory cells, including random access memory (RAM), read-only memory (ROM) and cache.

● Read-only memory (ROM)

ROM stands for read-only memory. When manufacturing ROM, information (data or programs) is permanently stored and preserved. This information can only be read, but generally cannot be written. Even if the machine is powered off, data will not be lost. ROM is generally used to store basic computer programs and data, such as BIOS ROM. Its physical appearance is usually a DIP integrated block.

● Random Access Memory (RAM)

Random access memory means that data can be read and written from it. When the machine loses power, the data stored in it will be lost. The memory chips we usually buy or upgrade are used as the memory of the computer. Memory stick (SIMM) is a small circuit board that gathers RAM integrated blocks together. It is inserted into the memory slot of a computer to reduce the space occupied by RAM integrated blocks. There are currently 1G//bar, 2G/ bar, 4G/ bar and so on.

Low speed cache (cache)

Cache is also a concept that we often encounter, that is, the first-level cache (L 1 cache), the second-level cache (L2 cache) and the third-level cache (L3 cache) that we usually see. It is located between CPU and memory, which is a kind of memory with faster reading and writing speed than memory. When the CPU writes or reads data into the memory, these data are also stored in the cache. When the CPU needs these data again, the CPU will read the data from the cache instead of accessing the slow memory. Of course, if the required data is not in the cache, the CPU will read the data in the memory again.

● Physical memory and address space

Physical memory and storage address space are two different concepts. However, due to the close relationship between the two, and the capacity is measured by B, KB, MB and GB, it is easy to be confused in understanding. Beginners understand these two different concepts, which is helpful to further understand memory and make good use of it.

Physical memory refers to a specific memory chip that actually exists. For example, the memory stick inserted in the motherboard and the ROM chip loaded with the system BIOS, the display RAM chip on the graphics card and the ROM chip loaded with the display BIOS, and the RAM chip and ROM chip on various adapter cards are all physical memories.

Memory address space refers to the range of memory coding (coded address). The so-called coding is to assign a number to each physical storage unit (a byte), which is usually called "addressing". The purpose of assigning a number to a storage unit is to facilitate searching and complete data reading and writing, which is called "addressing" (therefore, it is also called address space).

The size of the address space and the size of the physical memory are not necessarily equal. Let's take an example to illustrate this problem: there are 17 rooms on a certain floor, and their numbers are 80 1 ~ 8 17. This 17 room is a physical object, and its address space is coded by three digits, ranging from 800 to 899 * * *100 address, which shows that the address space is larger than the actual number of rooms.

For microcomputers above level 386, the address bus is 32 bits, so the address space can reach the 32nd power of 2, which is 4GB. (But our common 32-bit operating system windows xp can only recognize or use 3.25G of memory at most. Even though 64-bit operating system vista can recognize 4G memory, it can only use 3.25G memory at most. )

Ok, now we can explain why there are different memory types, such as regular memory, reserved memory, upper memory, high-end memory, extended memory and extended memory.

Twelve, the concept of microprocessor

Microprocessor (MPU) is a miniaturized CPU. That is, using VLSI technology to make CPU in one chip or several chips.

Thirteen, computer security knowledge

What is malware?

A: Malware is a general term for software that destroys the normal operation of the system. Generally speaking, it has the following manifestations:

Forced installation, unable to uninstall.

Modify the home page after installation and lock it

Automatically pop up advertisements at any time after installation.

Like a virus, self-replicating code will slow down the system.

What is a plugin?

A: Plug-ins are programs that are automatically executed with the start of IE browser. According to the loading position of the plug-in in the browser, it can be divided into toolbar, browser assistant (BHO), URL SEARCHHOOK and downloading ActiveX.

Some plug-ins can help users browse the Internet or call online auxiliary functions more conveniently, and some programs are called adware or spyware. This kind of malicious plug-in will monitor users' online behavior and report the recorded data to the creator of the plug-in program, so as to achieve illegal purposes such as placing advertisements, stealing games or bank account passwords.

Because plug-ins are issued by different publishers and have different technical levels, plug-ins are likely to conflict with other running programs, resulting in various page errors, running errors and other phenomena, which hinder normal browsing.

What is a Trojan horse?

A: Trojan horse is called "Trojan horse" in English, and its name is taken from the Trojan horse in Greek mythology. It is a hacker tool based on remote control, which has the characteristics of concealment and unauthorized. The so-called concealment means that the designers of Troy will use various means to hide Troy in order to prevent it from being discovered, so that even if the server finds that it is infected with Troy, it can only look at the horse and sigh, because it is impossible to determine its specific location. The so-called unauthorized means that once the control terminal is connected to the server, the control terminal will enjoy most of the operating rights of the server, including modifying files, modifying the registry, controlling the mouse and keyboard, etc. And these rights are not given by the server, but stolen by the Trojan horse program.

What are the hazards of Trojans?

1. Send QQ and msn tail numbers to trick more people into visiting malicious websites and downloading Trojans.

2. Steal the user's account, and achieve the purpose of illegally obtaining virtual property and transferring online funds through the stolen account and password.

3. Monitor users' behaviors and obtain important information of users.

How to guard against trojans?

1. Develop good online habits and don't visit bad small websites.

2. Download the software to a large download website or the official website of the software as much as possible.

3. Install antivirus software and firewall, and scan viruses and Trojans regularly.