3.2 The Fetch, Decode and Execute Stages

Question 1

What is the funtion of the RAM?

Answer 1

All inputs are stored in the RAM. Data that needs to be accessed from secondary storage is fetched into the RAM which can be directly accessed by the CPU.

Question 2

What components are used during the fetch stage?

Answer 2

• RAM
• PC
• MAR
• MDR
• CU
• CIR

Question 3

What happens during the fetch stage?

Answer 3

• Input is made and instruction stored in RAM.
• Address of next instruction to be processed stored in PC.
• Address in PC copied to MAR via address bus.
• Address copied into RAM via address bus and data is located within the RAM.
• Data is copied to MDR via data bus.
• Data is copied to CIR via data bus.

Question 4

What happens during the Decode stage?

Answer 4

• The data is held in the CIR which is located inside the CU.
• The CU reads and decodes the data into a predetermined instruction set that is processable by the ALU.

Question 5

What happens during the Execute stage?

Answer 5

• The ALU computes any mathmatical and logical calculations.
• Output is made.