Structure and Function of the processor

1. Why is the Memory Data Register (MDR) known as the gateway to the processor?

The Memory Data Register (MDR) temporarily stores data that has been read from memory or is about to be written to memory. All data entering or leaving the CPU must pass through the MDR.

2. What happens to the Program Counter (PC) at the start of each fetch-decode-execute cycle?

The address stored in the Program Counter is copied to the Memory Address Register (MAR).

3. What is the function of the Program Counter (PC)?

The Program Counter (PC) stores the address of the next instruction to be fetched from memory.

4. What is the function of the Memory Address Register (MAR)?

The Memory Address Register (MAR) stores the address of the memory location that is to be accessed.

5. What is the difference between the Program Counter (PC) and the Memory Address Register (MAR)?

The Program Counter stores the address of the next instruction to be fetched, whereas the Memory Address Register stores the address of the memory location currently being accessed.

6. What is the function of the Memory Data Register (MDR)?

The Memory Data Register (MDR) stores data that has been read from memory or data that is about to be written to memory.

7. What is the function of the Current Instruction Register (CIR)?

The Current Instruction Register (CIR) stores the instruction that is currently being decoded or executed.

8. What two parts make up an instruction stored in the Current Instruction Register (CIR)?

An instruction consists of an opcode and an operand.

9. What is the function of the Control Unit (CU)?

The Control Unit coordinates and controls the activities of the processor by sending control signals to other components.

10. What is the function of the Arithmetic Logic Unit (ALU)?

The Arithmetic Logic Unit performs arithmetic operations and logical operations on data.

11. Give examples of arithmetic operations carried out by the ALU.

Arithmetic operations include addition, subtraction, multiplication and division.

12. Give examples of logical operations carried out by the ALU.

Logical operations include AND, OR, NOT and comparison operations.

13. What is the function of the Accumulator?

The Accumulator stores intermediate data and the results of calculations performed by the ALU.

14. Why are registers faster than main memory?

Registers are located inside the CPU and can be accessed more quickly than main memory.

15. Why do processors with more registers often perform better?

More registers allow more data to be stored inside the CPU, reducing the need to access slower main memory.

16. What is the purpose of the Address Bus?

The Address Bus carries memory addresses from the CPU to memory and other devices.

17. Why is the Address Bus unidirectional?

The Address Bus only carries addresses from the CPU to memory, so data flows in one direction.

18. What is the purpose of the Data Bus?

The Data Bus carries data between the CPU, memory and other devices.

19. Why is the Data Bus bidirectional?

The Data Bus carries data both to and from the CPU.

20. What is the purpose of the Control Bus?

The Control Bus carries control signals between components of the computer system.

21. Why is the Control Bus bidirectional?

The CPU both sends and receives control signals, so communication must occur in both directions.

22. What is a mnemonic in assembly language?

A mnemonic is a short abbreviation that represents a machine code instruction.

23. What does the mnemonic LDA mean?

LDA means Load Accumulator.

24. What is the purpose of the Decode Unit?

The Decode Unit interprets the opcode of an instruction and determines the operation that must be carried out.

25. What is the purpose of the Status Register?

The Status Register stores flags that indicate the current state of the processor.

26. What is a flag?

A flag is a single bit in the Status Register that indicates whether a particular condition is true or false.

27. What is the purpose of the clock in a processor?

The clock generates regular timing pulses that synchronise the activities of the processor.

28. What is meant by clock speed?

Clock speed is the number of clock cycles generated per second and is measured in hertz (Hz).

29. What does a clock speed of 3.4 GHz mean?

It means the processor clock generates approximately 3.4 billion clock cycles per second.

30. What is the purpose of the Interrupt Register?

The Interrupt Register stores information about pending interrupts that require attention from the processor.

31. What happens when an interrupt is detected?

The processor temporarily stops its current task and executes an Interrupt Service Routine (ISR).

32. Give an example of a hardware interrupt.

A key being pressed on a keyboard is an example of a hardware interrupt.

33. What is cache memory?

Cache memory is a small amount of high-speed memory that stores frequently used data and instructions.

34. Why is cache memory faster than RAM?

Cache memory is physically closer to the CPU and can therefore be accessed more quickly.

35. What is the disadvantage of cache memory?

Cache memory has a much smaller capacity than RAM.

36. What are the three common levels of cache memory?

The three common levels of cache memory are L1, L2 and L3 cache.

37. Which CPU component sends memory read and memory write signals?

The Control Unit sends memory read and memory write signals using the Control Bus.

38. Which register stores the address of the memory location currently being accessed?

The Memory Address Register (MAR) stores the address of the memory location currently being accessed.

39. Which register stores data being transferred between memory and the CPU?

The Memory Data Register (MDR) stores data being transferred between memory and the CPU.

40. Which relationship between registers is commonly tested in OCR A-Level Computer Science?

At the start of the fetch-decode-execute cycle, the contents of the Program Counter are copied to the Memory Address Register.