1.1 Fetch-decode-execute cycle 1

Question 1

fetch

Answer 1

instructions and data are tranferred from the RAM to the CPU

-program instructions and data are stored in random access memory (RAM)

• the CPU sends a signal to the RAM requesting the next instruction to be executed
• the instruction is sent from the RAM to the CPU

Question 2

how does data move between the RAM and the CPU?

Answer 2

data bus from RAM to CPU

address bus from CPU to RAM

Question 3

decode and execute

Answer 3

instructions are interpreted and carried out

• program instructions/data from RAM enter the CU (within the CPU)
• the CU decodes the instruction and executes it
• if a calculation needs to be done the ALU is instructed

Question 4

State what is done at each stage of the fetch-decode-execute cycle [3]

Answer 4

fetch: the next instruction to be executed is transferred from the RAM to the CPU
decode: the CU interprets the instruction

execute: the CU carries out the instruction
it instructs the ALU if calculations need to be performed

Question 5

Explain how program instructions stored in computer memory are processed by the central processing unit [3]

Answer 5

during the ‘fetch’ phrase of the fetch-decode-execute cycle, the CPU sends a signal to the main computer memory requesting the next instruction to be executed

this instruction is decoded or interpreted by the CU and executed - carried out

if calculations are required, these are carried out by the ALU