instruction exexution cycle.

the CPU executes each instruction in a series of small steps. the steps are as follows.

1. fetch the instruction from the memory into the instruction register.
2. change the program counter to point the following instruction.
3. determining the type of instruction just fetched.
4. if the instruction uses a word in memory,determine where it is.
5. fetch the word,if needed into a CPU register.
6. execute the instruction
7. Go to step 1 to begin executing the following instruction.

this sequence is also known as fetch-decode-execution cycle.