1, ASCII code (american standard code for information interchange code)
(1) Letters, punctuation marks, special symbols and numbers used as symbols are generally called characters. These characters are represented by American standard information interchange code, abbreviated as ASCII code.
(2) Look-up table method of ASCII code (Appendix I of textbook P3 1 1 page): ASCII code is represented by 7-bit binary number (or 8-bit binary number with the highest bit of 0); The column in the table represents the 654th bit, the row represents the 32 10 bit, and the *** 128 code. Look up the table according to the first column before reading.
(3) The sizes of characters are compared according to their ASCII codes. ASCII codes of commonly used characters (from small to large): spaces-numbers-uppercase letters-lowercase letters.
For example, the ASCII code value of A is (100001) 2 = (41)16 = 65; The decimal value of ASCII code of f can be calculated as 70 [difference 5] from a; According to the table, the ASCII code value of A [65] is less than that of A [97], that is, the ASCII code value of lowercase letters is greater than that of uppercase letters.
2. Chinese character coding
In order to express Chinese characters with 0, 1 code string, China has formulated the Chinese character information exchange code GB23 12-80, which is referred to as the national standard code for short.
(1) The national standard code * * * has 7445 characters. 3755 first-class Chinese characters, arranged in the order of Chinese Pinyin; There are 3008 second-level Chinese characters, arranged by radicals and strokes.
(2) Because there are many characters in Chinese characters, each symbol of the national standard code is represented by a two-byte (16-bit binary) code.
1. GB code: 94(0-93) in each row and column, which is represented by the double 7-bit binary number in the first column, that is, the most significant bit of two bytes is 0 (see textbook P77). Location code: It is not convenient to use binary country code to represent, so Chinese characters can also be represented by decimal location code.
(1) The area (row) and the bit (column) are 94( 1-94) respectively, which are expressed by double 2-digit decimal numbers. The first area and the second position are preceded by 0.
(2) See Appendix 2 of the textbook P3 12 for the position code table. Figure 1-3 is a partial position code table, such as Fu 24032435；; Each 2487 map 1-3
3. Built-in code: the code actually used to represent Chinese characters in the computer. In microcomputers, double-byte codes (the highest bit is 1) are often used as built-in codes.
4. Three kinds of code conversion:
(1) converts the area code and location number from decimal to corresponding hexadecimal, and then +2020H is the national standard code (where h stands for 16 hexadecimal number);
(2) Hexadecimal national standard code +8080H is the internal code. It can be seen that the highest bit of the two bytes of the internal code must be 1 (the national standard code is 0).
For example, the area code of Chinese characters is 2083, the country code is 1453H+2020H=3473H, and the internal code is 3473H+8080H=B4F3H.
There are two kinds of computer calculation: numerical calculation (the most basic is four operations) and non-numerical calculation (the most basic is logical operation).
3. Four operations
Addition is the most basic of the four operations, and other operations can be realized by addition. Binary addition rule: 0+0 = 00+1=1+0 =1+10 binary multiplication rule: 0 * 0 = 00 * 65438. 1= 1 1.3.2 basic logical operations (P 13 table 1.2) There are three basic logical operations: AND, or NAND. The following 0 and 1 are binary codes. General 1 means positive (true) and 0 means negative (false) events.
1. logic and rules (when both a and b are true, the values of a and b are true, otherwise they are false. )
0 and 0 = 0, n, 0 and 1 = 0nn 1 and 0 = 0nn 1 and 1 = 1 (or 0? 0=0 0? 1=0 1? 0=0 1? 1= 1)
2. Logic or rule (when one of A and B is true, the value of A or B is true, otherwise it is false. ) 0or0 = 0n0or1=1nn1or0 =1n1=1(or 0+0 = 0+/kloc-. ) NOT 0= 1 nnNOT 1=0 (inversion)
4. Composition of computer system
(1) The computer system includes hardware system and software system.
(2) A hardware system is a collection of all physical components that make up a computer; A software system is the sum of various programs and documents.
5. Computer hardware system
The hardware consists of five parts: arithmetic unit, controller, memory, input device and output device.
1. arithmetic unit: the main part of a computer, which performs arithmetic and logical operations.
2. Controller: It takes instructions from the memory one by one, controls the coordination of all parts of the computer, and is the command center of the computer.
Step 3 remember
(1) The storage part of the computer is used to store the original data and programs.
(2) The memory is divided into storage units according to 8-bit binary bits or multiples thereof, and each unit has a number, that is, an address.
(3) The storage capacity is calculated in bytes:
A. the 8-bit binary number is 1 byte [byte], and it is recorded as1b; 1024[2 to the power of 10] bytes are recorded as1kb; 1024KB is recorded as1MB; 1024MB is recorded as 1GB. B. Byte unit conversion relation: 65438+GB =1024 MB =1024×1024 KB =1024×1024b.
(4) Memory is divided into internal memory (main memory) and external memory (auxiliary memory):
A. Memory is a kind of semiconductor memory, which is divided into read-only memory (ROM) and random access memory (RAM). Memory usually refers to the external storage of RAM, mainly magnetic media storage, including disks (floppy disks, hard disks), tapes, optical disks, etc.
B. The B.CPU can directly access the memory, and the externally stored data must be transferred to the memory before operation, so the memory is the center of computer information exchange. C. The memory access speed is fast, the storage capacity is small, and information will be lost when power is cut off; External memory has slow access speed and large storage capacity, and can store data permanently. 4. Input device: the original data and programs are converted into 0, 1 code strings that can be recognized by the computer and input to the computer. Commonly used input devices are keyboard, mouse, microphone, scanner, light pen, teleprinter, etc.
5. Output device: converts the information processed by the computer into a familiar form or outputs the information recognized by other devices to the outside of the computer. Common output devices include monitors, printers, speakers, plotters, etc. note:
(1) The controller and the arithmetic unit form the core of the computer, which is called the central processing unit (CPU).
(2)CPU and memory are collectively called the host.
(3) Input, output devices and external memory are collectively referred to as external devices.
Note: Although the disk drive is a storage device, it also has dual functions of input and output, so it can be used as an input and output device.
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