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The instruction cycle (also known as the fetch–decode–execute cycle, or simply the fetch–execute cycle) is the cycle that the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions. It is composed of three main stages: the fetch stage, the decode stage, and the execute stage.
The number of dependent steps varies with the machine architecture. For example: The 1956–61 IBM Stretch project proposed the terms Fetch, Decode, and Execute that have become common. The classic RISC pipeline comprises: Instruction fetch; Instruction decode and register fetch; Execute; Memory access; Register write back
The instruction cycle (also known as the fetch–decode–execute cycle, or simply the fetch-execute cycle) is the cycle that the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions. It is composed of three main stages: the fetch stage, the decode stage, and the execute stage.
In a typical fetch-decode-execute cycle, each step of a macro-instruction is decomposed during its execution so the CPU determines and steps through a series of micro-operations. The execution of micro-operations is performed under control of the CPU's control unit , which decides on their execution while performing various optimizations such ...
Nearly all CPUs follow the fetch, decode and execute steps in their operation, which are collectively known as the instruction cycle. After the execution of an instruction, the entire process repeats, with the next instruction cycle normally fetching the next-in-sequence instruction because of the incremented value in the program counter. If a ...
Both CPUs evaluate branches in the decode stage and have a single cycle instruction fetch. As a result, the branch target recurrence is two cycles long, and the machine always fetches the instruction immediately after any taken branch. Both architectures define branch delay slots in order to utilize these fetched instructions.
The fetch and decode stages is separated from the execute stage in a pipelined processor by using a buffer. The buffer's purpose is to partition the memory access and execute functions in a computer program and achieve high performance by exploiting the fine-grain parallelism between the two. [41]
Decode the instruction. If the instruction uses data stored in another mailbox then use the address field to find the mailbox number for the data it will work on, e.g. "get data from mailbox 42") Fetch the data (from the input, accumulator, or mailbox with the address determined in step 4) Execute the instruction based on the opcode given