Basic concepts of computer instructions

Computer instructions are instructions and commands that direct the work of the machine. A program is a series of instructions arranged in a certain order. The process of executing the program is the working process of the computer.

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

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Usually an instruction includes two aspects: operation code and operand , the operation code determines the operation to be completed, and the operand refers to the data participating in the operation and the unit address where it is located.

In computers, operation requirements and operand addresses are represented by binary numbers, called operation codes and address codes respectively. The entire instruction is stored in the memory in the form of binary encoding.

The type and number of instructions are related to the specific model.

Execution program

The sequential execution of the instructions will complete the execution of the program, so it is necessary to understand the execution process of the instructions. The first is to fetch and analyze instructions. According to the order specified by the program, the currently executed instructions are fetched from the internal memory and sent to the instruction register of the controller. The fetched instructions are analyzed, that is, what operations the computer should perform are determined based on the operation codes in the instructions.

The second is to execute the instructions. According to the instruction analysis results, the controller issues a series of control potentials required to complete the operation in order to direct the relevant components of the computer to complete the operation. At the same time, it is also ready to fetch an instruction.

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