Chapter 1.1 (The processor and processor components)

Question 1

What are the components of a CPU?

Answer 1

• Control unit (CU)
• Buses
• Arithmetic/Logic unit (ALU)
• Dedicated registers

Question 2

What is the function of the Control Unit?

Answer 2

• The Control unit controls and co-ordinates the activities of the CPU.
• It directs the flow of data between the CPU and other devices.
• It performs the fetch-decode-execute cycle

Question 3

What is a bus?

Answer 3

A bus is a set of parallel wires connecting two or more components of a computer

Question 4

What are the three busses collectively known as?

Name them

Answer 4

• They are known collectively as the system bus

- Consisting of the address, data and control bus

Question 5

What is the control bus?

Answer 5

The control bus is a bi-directional bus that transfers command, timing and specific status information between system components

Question 6

What is the data bus?

Answer 6

The data bus is a bi-directional path for moving data and instructions between system components

Question 7

What is the address bus?

Answer 7

The address bus is a bus that transmits the memory addresses of data that is used as operands in program instructions.

Question 8

What is the function of the ALU?

Answer 8

The arithmetic logic unit performs calculations and Logic operations.

Question 9

What are the Registers in the CPU?

Answer 9

• Accumulator
• Program counter (PC)
• Current Instruction Register (CIR)
• Memory Address Register (MAR)
• Memory Data Register (MDR)

Question 10

What is the function of the accumulator?

Answer 10

The accumulator is the register where operations carried out in the ALU are stored

Question 11

What is the function of the Program Counter?

Answer 11

The program counter (PC) is the register that holds the address of the next instruction to be carried out

Question 12

What is the function of the Current Instruction Register?

Answer 12

The Current Instruction Register (CIR) holds the current instruction being carried out as an Opcode and an Operand

Question 13

What is the function of the Memory Address Register?

Answer 13

The Memory Address Register (MAR) holds the address of the memory location from which the data is to be fetched from or written to

Question 14

What is the function of the Memory Data Register?

Answer 14

The Memory Data Register (MDR) is used to temporarily store the data read from or written to memory

Question 15

What happens in the Fetch stage of the Fetch-Decode-Execute cycle?

Answer 15

1 - The address of the next instruction from the Program counter is copied to the Memory Address Register
2 - The instruction located at the Address from the MAR (Via the address bus), is copied into the MDR
3 - simultaneously the PC is incremented
4 - The contents of the MDR are then copied into the CIR

Question 16

What happens in the Decode stage of the Fetch-Decode-Execute cycle?

Answer 16

1 - The instruction held in the CIR is split into opcode and operand
2- The Opcode determines the type of instruction
3 - the operand holds the data that will either:
+ Be the actual data to be operated on
and so gets copied to the MDR
+ Be the address of the data to be used
and so gets copied to the MAR

Question 17

What happens in the Execute phase of the Fetch-Decode-Execute cycle?

Answer 17

• Whatever the instruction/opcode was will be carried out

- It will receive a signal from the control bus letting it know whether it will write or read from memory