INSTRUCTION CYCLE

INSTRUCTION CYCLE

PROGRAM  :  A program is set of instructions.

* instructions are generally executed by the computer in sequential manner.

This cycle for every instruction is known as the instruction cycle.

COMPOSITION  OF INSTRUCTION CYCLE

The cycle consists of the following steps -

  

 

INSTRUCTION FETCH

In this step instruction which has to be executed , is fetched through data bus.

Initially CPU (central processing unit) transfers the address of the next instruction (to be fetched from memory) from the program counter (pc) to the memory address register (MAR).

MAR sends it to the memory through the address bus.

  

Finally, instruction is fetched from memory through data bus.

 

DECODING

In this step fetched instruction is decoded (In Machine Language).

OPERAND FETCH

In this step Operand is fetched from the memory.

* Depending on the Effective Address (EA) , Operand may reside in CPU registers or in memory.

NOTE : FOR MORE INFORMATION PLEASE VISIT PREVIOUS POSTS.

EXECUTION

After Instruction and Operand fetching we have both the Opcode & Operand.

Once the instruction gets decoded the processor executes the instruction.

* Arithmetic and Logic Unit (ALU) inside CPU executes the instructions.

RESULTS

After all the processing result is stored back in the memory at appropriate places.