Instructions and Programs_Chang ping China focuses on high quality website construction - 上海1314龙凤鲜花坊_上海419贵族宝贝

In short, computer instructions are instructions and commands to command computer work, programs are a series of instructions arranged in a certain order, and computer work process is the process of executing programs.

1. Instructions

The controller in the computer commands the work of the machine by instructions. People use instructions to express their intentions and give them to the controller for execution. Generally, an instruction includes two aspects: operation code and operand. The operation code determines the operation to be completed, and the operand indicates the data involved in the operation and the address of the unit where it is located.

In a computer, instructions are stored in memory in the form of binary code.

During the execution of an instruction, the first step is to fetch the instruction and analyze the instruction, that is, according to the order specified by the program, fetch the currently executed instruction from the memory Website Design The instruction is sent to the instruction register of the controller to analyze the instruction taken, that is, determine what operation the computer should perform according to the operation code in the instruction. The second is to execute the command, that is, according to the command analysis results, the controller sends a series of control signals needed to complete the operation, so as to command the relevant components to complete this operation, and also prepare for taking down a command.

2. Command system

The whole set of different instructions that a computer can execute is called the instruction system of the computer. Each computer has its own specific instruction system, and its instruction content and format are different.

Although the instruction systems designed for different CPUs are different, basically all computers include the following types of instructions: data transmission instructions, input/output (I/O) instructions, arithmetic operation instructions, logic operation instructions, shift operation instructions, program control instructions, serial operation instructions, processor control instructions, data conversion instructions, etc.

In the process of optimization and development of computer instruction system, there have been two completely different optimization directions: Complex Instruction Set Computer (CISC) technology; Reduced Instruction Set Computer (RISC) technology. The computer instructions here refer to the machine instructions at the lowest level of the computer, which can be directly recognized by the CPU.

The computer system is becoming more and more complex, and the construction of its instruction system is required to make the overall performance of the computer system faster and more stable. At first, the optimization method adopted by people was to set some instructions with complex functions, and change some commonly used functions to be implemented by software to hardware instruction system, that is, to obtain high performance by increasing the complexity of hardware, which is the idea of CISC technology.

The increasingly complex instruction system is not only difficult to implement, but also may reduce the system performance. In 1979, a group of computer scientists led by Professor Patterson began to carry out this research at the University of California, Berkeley. The results show that the usage rate of various instructions in computers is very different: 80% of the instructions used in the operation of a typical program are only 20% of the instructions in its instruction system. In fact, the most frequently used instructions are simple instructions such as store, fetch, and add. Therefore, the long-term commitment to the design of complex instruction systems is actually to design an instruction system processor that is difficult to use in practice.

RISC technology was developed in the 1980s. Its basic idea is to simplify the computer instruction function as much as possible, and only retain those instructions that are simple in function and can be executed within a beat, while using a section of subroutine to implement more complex functions.

3. Procedures

Computer program (commonly referred to as program, which is called program in Hong Kong, Macao and Taiwan regions of China) refers to a sequence of instructions organized according to certain rules and ideas that can correctly complete the specified work. Today's computers cannot directly understand human natural language, so they cannot write computer programs in natural language. Programs are usually written in a programming language and run on a target machine.

Programming (that is, programming, whose professional term is "programming") is a systematic and tedious work, which requires programmers to have corresponding professional basic knowledge, as well as good programming habits and styles. Just like building a house, we should first design the drawings and then start the construction.

The process of programming includes problem analysis, structural design, user interface design, code design and debugging, maintenance, etc. Generally speaking, problem analysis is to clarify what functions and effects the program will achieve, and structural design is to design the overall framework of the program; User interface design refers to the design of the input/output interface that interacts with the user when the program runs; Code design is to write program code, and then eliminate errors in the program as far as possible through debugging to ensure the functionality and correctness of the program; For programs in use, 9 maintenance shall be carried out to correct errors or upgrade functions and performance.

Instructions and procedures

Date：2015-06-17 Source: Shangpin China Type: website encyclopedia
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