How does the CPU execute instructions in a computer system?

The CPU executes instructions in a computer system through a process known as the fetch-decode-execute cycle.

The Central Processing Unit (CPU) is the brain of the computer, responsible for executing instructions of a computer program. This process is carried out through a cycle known as the fetch-decode-execute cycle, also referred to as the instruction cycle. This cycle is a set of operations that the CPU performs to execute each machine language instruction of a program.

The first step in this cycle is the fetch operation. The CPU fetches the instruction from the main memory (RAM) into its own internal memory, the Instruction Register (IR). The Program Counter (PC) keeps track of the memory address of the next instruction to be fetched. After fetching, the PC is incremented to point to the next instruction.

The second step is the decode operation. The Control Unit (CU) of the CPU decodes the fetched instruction to determine what operation needs to be performed. This could be an arithmetic operation, a data movement operation, or a control operation. The CU uses the opcode (operation code) of the instruction to determine the type of operation.

The final step is the execute operation. The CPU performs the operation as determined by the decode step. This could involve the Arithmetic Logic Unit (ALU) if it's an arithmetic or logical operation, or it could involve moving data from one register to another, or from memory to a register. If the operation is a control operation, it could involve changing the sequence of execution of the program, such as in the case of a jump instruction.

This cycle repeats for each instruction in the program until the program ends. The speed at which the CPU can complete this cycle, often measured in cycles per second or hertz, is a key factor in the overall performance of a computer system. The CPU's ability to execute multiple instructions simultaneously, known as parallel processing, can also significantly enhance performance.