Principle of computer calculation

The working process of a computer is essentially the process of executing a program, which is composed of several instructions. By executing the instructions in the program one by one, the computer can complete the execution of a program, thus completing a specific task. Therefore, understanding the working principle of the computer is to understand the basic process of instructions and instruction execution.

1. Description and procedure

The reason why the computer can automatically calculate without direct human intervention is that human beings input step-by-step operation instructions (that is, instructions) into the memory in advance, and when they are executed, the machine takes out these instructions one by one for analysis and execution.

Usually one instruction corresponds to a basic operation. What instructions the computer can execute and how many instructions it has are decided by the designer when designing the computer. All instructions that a computer can directly execute are computer instruction sets.

Instructions expressed in binary code are called machine instructions, which usually include two parts: operation code and operand. The operation code indicates what operation the computer performs, and the operand indicates the number itself or the address where the operand is located. Because the computer only knows binary numbers, all instructions in the computer instruction system must be expressed in the form of binary codes.

Procedures are steps to solve problems. The computer problem-solving program must be described in a language that the computer can recognize, so the program is a collection of instructions, and the problem-solving steps described by instructions are called programs.

2. Instruction execution process

According to von Neumann's idea of stored programs, to solve problems with computers, first of all, the instruction sequence (that is, the program) and the original data indicating how the computer operates should be transported to the computer's memory through input devices. When the computer is running, the instructions are taken out from the memory in turn, and the controller analyzes and judges the instructions, sends out different control signals according to the instruction requirements, and completes the specified operations under the command of the controller until all the operations are completed. Therefore, the working principle of computer can be summarized as stored program and program control.

Generally speaking, the time required for a computer to complete an instruction is called an instruction cycle. The shorter the instruction cycle, the faster the instruction execution. The main frequency or working frequency of CPU usually reflects the length of instruction execution cycle.

When the computer runs, the CPU reads an instruction from the memory and executes it in the CPU. After the instruction is executed, the next instruction is read from the memory and executed in the CPU. The CPU keeps fetching instructions, analyzing instructions and executing instructions, which is the execution process of the program.