2.1.4 - Instruction Cycle

Explain Step 1 - fetching an instruction

-CPU fetch's instruction and data into CPU. -a value is placed in the PC to indicate the address of the instruction that is to be carried out. -value passed to memory address register so instruction or data stored there can be located. -value sent to memory to locate address (using address bus) -Data stored in memory address is sent to MDR using data bus.

Explain Step 2 - Decoding Instruction

-To process instruction, CPU needs to understand instruction. Process called 'decoding' an instruction, CPU uses instruction set. -This is a set of commands that are written in machine language CPU understands.

Explained Step 3 - Executing instruction

-Where actions required by instruction takes place. Such as, any calculations that need to be carried out using the data.

what is the fetch-execute cycle?

-basic operation of a computer is called 'fetch-execute cycle' (or 'machine cycle') -Computer fetched instruction from memory and executes it. -Done repeatedly from when computer is booted up to when it is shut down.

What is the fetch-decode-execute cycle?

.Process CPU goes through to process an instruction. At start of cycle, both the data and instructions are loaded into computer's main memory so they're ready to be processed. It is the computer's operating system that loads them into place.

What does an instruction look like?

Is in binary so computer will always know what to do and where to find the thing it needs. -It is split into two parts, the opcode and operand.

Opcode

tells CPU what is to be done

Operand

tells CPU where to do it