Basic knowledge of computer science (Part 1)

outline

1. The development, types and fields of application of computers
2. Representation, storage and processing of data in computers
3. The composition and main technical indicators of computer software and hardware systems .
4. The basic concept, function, composition and classification of the operating system .
5. Basic concepts and common terms of Windows operating system , files, folders, libraries, etc.
6. The concept and application of multimedia technology
7. The concept, characteristics, classification and prevention of computer viruses .
8. The concept, composition and classification of computer network ; the concept and prevention and control of computer and network information security
   .
9. The concept, principle and application of Internet network service .
10. Basic knowledge of databases , and commonly used database systems

Explanation by unit

1. The development, types and application fields of computers

development of computer technology

Since the birth of the world's first computer ENIAC in 1946 , computer technology has developed rapidly.

The picture below shows the world's first computer ENIAC :

The picture below shows China's first computer 103 :

According to the different electronic devices used in computers , computers have experienced four eras: tubes, transistors, integrated circuits, large-scale and ultra-large-scale integrated circuits .

1. The main characteristics of the first generation of electronic tube computers (1946-1958) are: in terms of hardware , electronic tubes were used as the basic logic circuit components, mercury delay lines, magnetic drums and magnetic cores were used in the main memory , and magnetic tapes were used in the external memory ; in terms of software , only machine language and assembly language could be used. The computer was bulky , power-consuming, poorly reliable, and expensive, and its applications were mainly scientific calculations .
   

2. 
   The main characteristics of the second-generation transistor computer (1958-1964) are: in terms of hardware , transistors are used as basic logic circuit components, magnetic cores are mainly used for main memory , and disks are used for external memory ; software has developed greatly, and various high-level languages ​​​​and compilers have appeared, and operating systems based on batch processing have appeared ; the size of the computer has been greatly reduced , power consumption has been reduced, and reliability has been improved; applications are mainly scientific calculations and various transaction processing , and began to be used in industrial control .

Transistor computer as shown in the figure:

3. 
   The main characteristics of the third-generation integrated circuit computer (1964-1971) are as follows: in terms of hardware , the main logic components of the computer used medium and small-scale integrated circuits , and the main memory began to use semiconductor memory ; in terms of software , the computer programming language was standardized , and the idea of ​​​​structural programming was proposed ; the size of the computer was further reduced, and the main performance indicators such as computing speed, computing accuracy, storage capacity and reliability were greatly improved; the application field and popularity of the computer developed rapidly .

Integrated circuit digital computer as shown in the figure:

The integrated circuit is shown in the figure:

4. The main characteristics of the fourth-generation large-scale and VLSI computers (since 1971)
   are: in terms of hardware , the computer logic components are composed of large-scale and VLSI , the main memory uses semiconductor memory , and the computer peripherals are diversified and serialized. In terms of software , software solid technology has been realized, and object-oriented computer programming ideas have emerged .
   In the development process of the fourth generation computer , one of the most important achievements is that the size of the microprocessor is continuously reduced, the degree of integration is continuously improved, and the calculation speed is getting faster and faster .

mac laptops:

mac laptop motherboards :

When it comes to the development of computers , one cannot fail to mention American scientist Von Neumann (the father of computers). In the mid-1930s, von Neumann proposed the theory of stored programs in electronic computers . Until today, this mechanism is still used inside the computer, and its characteristics are: the computer is composed of five parts: controller, arithmetic unit, memory, input device, and output device .

• Input devices (such as keyboards) are used to enter raw data and instructions;
• The controller sends various control signals to other components of the computer according to the instructions given by the user ;
• Calculators are used to perform calculations on data ;
• The memory is used to store the results before and after data processing ;
• Output devices (such as display screens) are used to output calculation results .
  
  The von Neumann system is as follows:

Computer application field

At the beginning of the advent of the computer, it was mainly used for numerical calculations , hence the name "computer" .

However, with the development of computer technology, its scope of application has been expanding . It is not limited to numerical calculations but is widely used in data processing, automatic control, computer-aided design, computer-aided manufacturing, computer-aided teaching, artificial intelligence, multimedia technology, computer networks and other fields.

1. Scientific Computing

Scientific computing, also known as numerical computing, is the earliest application field of computers . Scientific computing refers to the calculations that computers use to complete mathematical problems raised in scientific research and engineering technology .

This type of calculation is often complex and difficult , because it is difficult for general calculation tools or manpower to complete. For example, weather forecasting requires solving differential equations that describe the laws of atmospheric motion . Launching a missile requires the calculation of the ballistic curve equation of the missile , which requires high-speed and accurate calculations by a computer.

2. data processing

Data processing refers to the process of managing and processing various data materials on the computer, so that people can obtain more useful information . For example, enterprise management, material management, report statistics, account calculation and information retrieval are all data processing.

3. automatic control

Automatic control refers to the behavior of using a computer to automatically operate a certain process . It does not require human intervention, and can carry out process control according to the goals and states predetermined by people, such as unmanned aircraft, missiles and artificial satellites .

4. computer aided system

Computer-aided systems include computer-aided design, computer-aided manufacturing, and computer-aided teaching . Among them, Computer-Aided Design (CAD) refers to the use of computers to help designers in engineering design .

Computer-aided manufacturing (Computer-Aided Manufacturing, CAM) refers to the use of computers to manage, control and operate production equipment , which plays a positive role in improving product quality, reducing costs and shortening production cycles.

Computer-Assisted Instruction (CAI) refers to the use of computers to assist students in learning . It stores teaching content, teaching methods, and student learning conditions in the computer, so that students can learn the knowledge they need from the CAI system.

5. artificial intelligence

Artificial Intelligence (AI) refers to allowing computers to simulate certain intellectual behaviors of humans . For example, a computer can be used to simulate some functions of the human brain for thinking, learning, reasoning, association and decision-making, so that the computer has a certain "thinking ability".

6. multimedia application

Multimedia (Multimedia) is the composition of various media such as text, animation, graphics, images, audio and video . In recent years, multimedia technology has been widely used in various industries and home entertainment.

7. computer network

Computer network is the product of the highly developed and closely integrated modern computer technology and communication technology. It uses communication equipment and lines to interconnect multiple computer systems with different geographical locations and independent functions, so as to realize resource sharing and information transmission in the network .

For example, the world's largest computer network, the Internet (Internet), has turned the entire planet into a small village, where people can easily search for information, download resources, communicate, learn, entertain and buy and sell things online .

2. Representation, storage and processing of data in computers

1. Data is a symbolic representation of objective things ;
2. The information in the computer is expressed in binary ;

We use the decimal system in our life , and the decimal number is a number system based on 10, consisting of ten basic numbers of 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 .

• The decimal system is based on the two principles of the base system and the decimal system , that is, all numbers are represented by 10 basic symbols , and the decimal one is full . At the same time, the same symbol has different values ​​​​in different positions , and the position of the symbol is very important.
• The basic symbols are the ten digits from 0 to 9.
• To represent 10 times of these ten numbers , these numbers are shifted to the left by one, and the vacant places are filled with 0, that is, 10, 20, 30, ..., 90;
• To represent 1/10 of these ten numbers , just move the position of this number to the right , and fill in the empty space with 0 when necessary: ​​0.1, 0.2, 0.3, ... , 0.9.

Computers use binary , and learning by analogy can make you learn faster and more firmly.

• Binary data is a number represented by two digits of 0 and 1 . Its base is 2, the carry rule is "every two makes one", and the borrow rule is "borrow one as two" .
• The computer base system designed in the early days was mainly decimal (because we have ten fingers, decimal is a more reasonable choice, and ten numbers can be represented by fingers, and the concept of 0 did not appear until a long time later, so it is 1-10 instead of 0-9).
• After the advent of electronic computers , it was too complicated to use electronic tubes to represent ten states, so there were only two basic states in all electronic computers , on (1) and off (0). In other words, the two states of the electronic tube determine that the electronic computer based on the electronic tube uses binary to represent numbers and data.
• ENIAC uses decimal, von Neumann proposed binary.

3. unit of data in a computer

Bit: the smallest unit of data , each number becomes one bit; (binary, each bit is 0 or 1)
Byte: the basic unit of storage capacity ;
byte (B), kilobyte (KB), megabyte (MB), gigabyte (GB), terabyte (TB);

Conversion relationship:

• 1 Byte=8 bit
• 1 KB=1024 B
• 1 MB=1024 KB
• 1 GB=1024 MB
• 1TB=1024GB

$1024=2^{10}$

4. Word length : The binary bits that a computer can process in parallel at one time is the word length of the machine.

The word length is an important symbol, which directly reflects the computing power and computing precision of a computer .
When other conditions are constant , the longer the word length, the faster the data processing speed of the computer .

5. common base

Binary (Binary): 1001B, suffixed with the abbreviation B of Binary, indicating that it is a binary number;

Octonary : 520O, as above, abbreviated O as a suffix to indicate an octal number;

Decimal : 520D, where D can be omitted, which is 520 used in our life;

Hexadecimal (Hexadecimal): 7FH, the abbreviation H is the suffix, or the beginning of 0x, such as 0x7F, all represent hexadecimal numbers. Hexadecimal is 0, 1, ..., 9, A, B, ..., F, where A represents 10, B is 11, C is 12, and up to F represents 15.

The base conversion is as follows,

Convert other bases to decimal :

• For example, convert binary to decimal, $1001B=1\times (2^3)+0\times (2^2)+0\times (2^1)+1\times (2^0)=9$
• For example, convert octal to decimal, $520O\_=5\times (8^2)+2\times \left(8^1\right)+0\times 8^0=336$
• Such as hexadecimal to decimal, $7FH\_\_=7\times (16^1)+F\times 16^0=7\times 16+15\times 1=127$
  Are You Abandoned? Binary remembers the four numbers 8, 4, 2, and 1. What does it mean?
  Only one picture is here!

Binary to other bases :

• Such as converting binary to octal: $10010111B=10010111B=227O\_$
• For example, convert binary to decimal: $10010111B=1\times 2^7+1\times 2^4+1\times 2^2+1\times 2^1+1\times 2^0=512+16+4+2+1=535$
• For example, convert binary to hexadecimal: $10010111B=10010111B=97F$
  is only one picture away!

6. memory
   

Random access memory (Random Access Memory, RAM ), also known as "random access memory", is an internal memory that directly exchanges data with the CPU , and is also called main memory (memory) .

RAM has the characteristics of random access and volatility ;

• The so-called "random access" means that when the data in the memory is read or written, the time required has nothing to do with the location of this piece of information or the location where it is written. RAM cannot retain data when the power is turned off.
• If data needs to be saved, they must be written to a long-term storage device (such as a hard disk). Compared with RAM and ROM, the biggest difference between the two is that the data stored on RAM will disappear automatically after power off, while ROM will not.

7. Chinese character encoding

ASCII only encodes English letters, numbers, and punctuation . (Remember that the code length of the international common ASCII code is 7)

Because it was invented by Wai Guoren, they speak English, and only need to encode 26 English letters, which is why the current C, C++, and Python codes are also written in English instead of Chinese.

The ASCII code is shown in the figure:

Chinese characters are divided into two levels:

• There are 3,755 first-level Chinese characters, arranged in the order of Chinese pinyin letters;
• There are 3008 second-level Chinese characters, arranged according to radicals.

Because one byte is enough to represent 6763 Chinese characters, a national standard code uses two bytes to represent a Chinese character, and the highest bit of each byte is 0.

The processing process of Chinese characters:
input—>input code—>national standard code—>internal code—>address code—>font code—>output

• Input code: the code compiled for inputting Chinese characters into the computer becomes Chinese character input code, also called external code;
• Internal code: Chinese character encoding for storing and processing Chinese characters inside the computer;
• Font code: used for outputting Chinese characters on the display screen or printer;
• Address code: refers to the address code of the Chinese character library. When it is necessary to output Chinese characters to the output device, the Chinese character library must be accessed through the address;

Other Chinese character codes:

• GBK code: (expanded Chinese character internal code specification) up to more than 20,000 simple and complex Chinese characters ;
• UCS code: contains alphabetic characters, Chinese, Japanese and Korean ideographic files;
• Unicode encoding: 65536 character encoding, mainly used to solve multilingual computing problems;
• BIG5 code: a traditional Chinese character code used in Hong Kong and Taiwan;

Commonly used encodings for .txt files include ANSI and UTF-8. Sometimes garbled characters appear when the file is opened , which means that the encoding format is wrong, as shown in the figure below:

3. Composition and main technical indicators of computer software and hardware systems

Composition of computer software and hardware system

• Computer system = software system + hardware system
• Hardware system = controller + arithmetic unit + memory + input + output
• Software system = system software + application software
• Software = Program + Documentation = Data Structure + Algorithm + Documentation

Among them, processor = controller + arithmetic unit , the processor is the brain of the computer, also called CPU.

• Software system is a general term for various programs, data and documents compiled for operating, managing and maintaining computers .
• Software : It is the soul of a computer, a computer without software is useless.
• Program : It is a set of instructions executed in a certain order to complete a certain task .
• Programming language : A language that people use to tell a computer to do something.

• Machine language: the language that the computer recognizes and executes directly;
• Assembly language: symbolic language, which needs to be compiled to execute;
• High-level language: close to natural language (compiled and interpreted);

hardware system

1. calculator

Arithmetic operations (addition, subtraction, multiplication, division) or logic operations (and, or, not, exclusive or) are performed on binary numbers , so they are also called arithmetic logic components.

1. And (AND, symbol: &)
   operation rules: all ones are one, and zeros are zero . That is, the result is 1 only when both operands are 1, and 0 in other cases (as long as there is 0, the result is 0).
   
   1 and 1 = 1, 1 AND 0 = 0, 0 & 0 = 0; all three expressions are acceptable.
2. Or (OR, symbol: |)
   operation rules: all zeros are zero, and one is one . That is, the result is 0 only when both operands are 0, and 1 in other cases (as long as there is 1, the result is 1).
   
   1 or 1 = 1, 1 OR 0 = 1, 0 | 0 = 0; all three expressions are acceptable.
3. NOT (NOT, symbol: $\bar{1}$ , a horizontal line above means not)
   logical NOT operation, there is only one operand, so it is a unary logical operation.
   Operation rules:One becomes zero, zero becomes one. That is, when the operand is 1, the result is 0, and when the operand is 0, the result is 1.
   $\bar{1}=0$，$\bar{0}=1$。
4. Exclusive OR (XOR)
   logical exclusive-or operation, operation rules: the difference is one, the same is zero . That is, the result is 1 when the two operands are different , and 0 when the two operands are the same .
   1 XOR 1 = 0, 0 XOR 0 = 0; 1 XOR 0 = 1, 0 XOR 1 = 1.

The computing speed of a computer usually refers to the number of addition instructions that can be executed per second , expressed in millions of operations per second (MIPS) .

2. controller

The controller is the heart of the computer , which directs the various components to work automatically and harmoniously .

Instruction execution process : fetch instruction -> analyze instruction -> generate control signal -> execute instruction -> repeat execution.

The PC always holds the address of the next instruction to be executed .
The arithmetic unit + controller is collectively called the central processing unit (CPU) , and the higher the clock frequency, the faster the speed.

3. memory

The components that store programs and data are divided into two categories: internal memory (main memory) and external memory (auxiliary storage).

• The memory speed is fast , and the information is lost when the power is off . Such as main memory RAM.
• External storage is slow , but information can be stored for a long time . Such as disk, U disk, etc.

Read and write speeds are arranged from fast to slow : registers (in the CPU) > CACHE (in the CPU) > RAM > ROM > external devices;

Due to the difference in read and write speeds, the CPU cannot directly deal with external devices, and it needs to use RAM or CACHE as an intermediary bridge .

Memory:

• Memory = read-only memory ROM + random access memory RAM (only) (random random)
• Random access memory RAM: commonly referred to as computer memory ;
• Read-only memory ROM: After curing, the user cannot change it ; (only readable, not writable)

Cache cache: It is mainly designed to solve the mismatch of the main memory speed of the CPU and to increase the storage speed .

External storage: cannot be directly accessed by CPU (hard disk, U disk, CD-ROM and floppy disk)

• Hard disk: read and write physical unit sectors
• Flash memory (Flash)
• CD

Hierarchy:

• Cache - main memory level (to solve the problem of speed mismatch )
• Main memory-auxiliary storage level (to solve the problem of memory system capacity )

Software system

system software

System software enables computer users and other software to treat the computer as a whole without concern for how the underlying individual pieces of hardware work . (For example, if you open a file, you only need to double-click the file on the Windows operating system, but you don’t know what the underlying hardware uses)

(1) Operating system

The operating system is a collection of systematic programs that control and manage computer resources . It is the interface between users and computer hardware systems , and provides a bridge for users and application software to access and control computer hardware .

Such as Windows, Linux, Unix, MacOS . (The Windows operating system is also what you want to test)

(2) Language processing program

Human-to-human communication requires language, and human-to-computer communication also requires language. The language used to communicate information between humans and computers is called a programming language .

Programming languages ​​are usually divided into three categories according to their dependence on hardware:

◆Machine language: It is a set of code instructions composed of binary codes "1" and "0". It is the only machine-oriented language that can be recognized and executed by computer hardware.
◆Assembly language: It is a symbolic language that uses some mnemonics that can reflect the function of instructions to replace machine instructions.
◆High-level language: It is an algorithmic language independent of the machine. The expression of high-level language is close to the natural language and mathematical expressions that people use every day, and has certain grammatical rules.

(3) Database management system

The database management system is mainly oriented to solve the non-numerical calculation problems of data processing, and to organize, manage and query a large amount of data stored in the computer . Commonly used database management systems include SQL Server, Oracle, Mysql, and Visual FoxPro.

(4) System support and service program

Such programs are also called tool software , such as system diagnostic programs, debugging programs, debugging programs, editing programs, virus scanning programs, etc., are all software systems configured to maintain the normal operation of the computer system or support system development.

application

Application software is the part of software provided to meet the application needs of users in different fields and problems . It can broaden the application fields of computer systems and amplify the functions of hardware .

Software development is the process of building a software system or a software part of the system according to user requirements .

Software development is a system engineering that includes requirement capture, requirement analysis, design, implementation and testing . (For example, if you want to entertain and pass the time, you have developed short video entertainment software such as Douyin Kuaishou)

• Word processing software such as WPS, Word, etc. (this part is also what you need to test)
• information management software
• Aided design software such as AutoCAD
• Education and entertainment software, such as LOL, Kuaishou

computer structure

The five major components of the computer hardware system do not exist in isolation , but need to be connected and transmitted with each other . The structure of a computer reflects how the various components of the computer are connected.

Computer bus structure (data bus, address bus, control bus)

• Data Bus (Data Bus): transfer data information
• Address Bus (Address Bus): transfer address information
• Control Bus (Control Bus): send command signals

Computer Key Performance Indicators

• Word length : the number of bits of binary data that the computer CPU can directly process;
• Clock frequency : the clock frequency of the computer CPU, the main frequency unit is megahertz (MHz) or gigahertz (GHz);
• Computing speed : generally described in millions of times per second (MIPS); the faster the better;
• Storage capacity : divided into memory capacity and external storage capacity;
• Access cycle : the time required for the CPU to access data from the memory, the shorter the access cycle, the faster the operation speed ;

self test

1. The main component of the second generation electronic computer is ______.

A. Relay

B. Transistor

C. Electron tube

D. integrated circuit

Answer: B

2. Which of the following is not a characteristic of electronic digital computers is ______.

A. Fast operation

B. High calculation accuracy

C. The shape is clumsy

D. Strong versatility

Answer: C

3. The field of ______ is one of the most attractive, difficult and currently researched fields in computer applications.

A. Aided design

B. Information processing

C.artificial intelligence

D. Process control

Answer: C

4. In the computer field, information is transformed into a ______ that a computer can process.

A. Data

B. Symbol

c. graphics

D. Numbers

Answer: A

5. The operation object of electronic digital computer is ______.

A. Analog

B. Mixing amount

C. Pulse

D. Discontinuous quantity

Answer: D

6. Among the following types of computer memory, the information in which will be lost after power failure is ______.

A.ROM

B.RAM

C. hard disk

D. Floppy disk

Answer: B

7. The number of bits in a microprocessor chip refers to ______.

A. speed

B. word length

C. Frequency

D. cycle

Answer: B

8. An input/output device essential to keep a microcomputer running is ______.

A. Keyboard and mouse

B. Monitors and Printers

C. Keyboard and monitor

D. Mouse and scanner

Answer: C

9. An important indicator that determines the performance of a microprocessor is ______.

A. The size of the memory

B. The size of the microprocessor

C. Frequency

D. Internal memory

Answer: C

10. The number of characters that can be represented by ASCII code is ______.

A.256

B.255

C.128

D.127

Answer: C

11. The decimal number corresponding to the binary number 10110001 should be ______.

A.123

B.167

C.179

D.177

Answer: D

12. The code used to process data and instructions inside a computer is ______.

A. Decimal code

B. Binary code

C.ASCII code

D. Chinese character encoding

Answer: B

13. Among the following options, ______ does not belong to the external equipment of the computer.

A. Input device

B. CPU and main memory

C. External memory

D. Output device

Answer: B

14. The necessary external equipment for a personal computer (PC) is ____.

A. Keyboard and mouse

B. Monitor and keyboard

C. Keyboard and printer

D. Monitors and Scanners

Answer: B

15. A command for a computer to perform a certain operation is called ______.

A. Instructions

b. program

c. programming language

D. command system

Answer: A