Ch.4 Operating systems and computer architecture

Question 1

What does a control bus do?

Answer 1

• Carries signals to synchronise the fetch-execute cycle
• Directs the CPU
• Can be unidirectional or bidirectional

Question 2

What does a data bus do?

Answer 2

• Carries data that is being processed

- Bidirectional

Question 3

What does an address bus do?

Answer 3

• Carries address locations of next item to be fetched

- Unidirectional

Question 4

List the 5 different registers

Answer 4

1. MDR
2. MAR
3. PC
4. CIR
5. ACC

Question 5

What is meant by the stored program concept?

Answer 5

• Programs / instructions are stored in memory
• Data is stored in memory
• Instructions are fetched and executed one after another

Question 6

Describe the role of the Program Counter

Answer 6

• Holds the address …

- … of next / current instruction

Question 7

What does a Program counter do?

Answer 7

• Increments to point to the address of the next instruction to be fetched

Question 8

What does an accumulator (ACC)?

Answer 8

It holds the result of a calculation,

It is located in the Arithmetic Logic Unit (ALU)

Question 9

What does a memory data register do (MDR)?

Answer 9

• Temporary storage between the central processing unit (CPU) and primary memory

Question 10

Describe the role of the ALU

Answer 10

− Carries out calculations
− Carries out logical operations
− Holds temporary / interim values during calculations
− …in a register called the accumulator (ACC)