1. OCR A Level (H046-H446) SLR1 – 1.1 ALU, CU, registers and bus

What is the primary function of the control unit inside a processor?

• It temporarily stores data read from or written to main memory.

• It stores the address of the next instruction.

• It performs arithmetic and logical operations.

• It coordinates all the activities of the processor.

Answer explanation

The control unit inside a processor coordinates all the activities of the processor, making it the primary function.

What does the program counter do?

• It directs the flow of data between the CPU and other devices.

• It performs arithmetic operations.

• It holds the address of the next instruction to be executed.

• It holds the current instruction being executed.

Answer explanation

The program counter holds the address of the next instruction to be executed, directing the flow of execution in the CPU.

What is the purpose of the memory address register?

• To hold the current instruction being executed.

• To hold the address of the memory location from which data or instruction is to be fetched.

• To temporarily store data read from or written to main memory.

• To coordinate the activities of the processor.

Answer explanation

The memory address register holds the address of the memory location from which data or instruction is to be fetched, making it the correct choice.

What is the function of the memory data register?

• To temporarily store data read from or written to main memory.

• To perform arithmetic and logical operations.

• To hold the address of the next instruction.

• To coordinate the activities of the processor.

Answer explanation

The memory data register functions to temporarily store data read from or written to main memory, making it the correct choice.

What does the current instruction register contain?

• Temporary data for calculations.

• The current instruction actually being executed.

• The address of the memory location to be fetched.

• The address of the next instruction.

Answer explanation

The current instruction register contains the current instruction actually being executed.

What operations does the ALU perform?

• It temporarily stores data read from or written to main memory.

• Arithmetic and logical operations.

• It stores the address of the next instruction.

• It coordinates processor activities.

Answer explanation

The ALU performs arithmetic and logical operations, making it the correct choice.

What is the purpose of general purpose registers in a CPU?

• To perform arithmetic and logical operations.

• To hold the address of the next instruction.

• To store temporary data while instructions or calculations are being carried out.

• To coordinate the activities of the processor.

Answer explanation

General purpose registers in a CPU are used to store temporary data while instructions or calculations are being carried out, making them essential for efficient processing.

What is the direction of information flow on the address bus?

• Circular

• Unidirectional, from main memory to processor

• Unidirectional, from processor to main memory

• Bi-directional

Answer explanation

The direction of information flow on the address bus is unidirectional, from processor to main memory.

What is the role of the data bus?

• To carry command and control signals.

• To carry the actual memory addresses.

• To carry the actual binary data being transmitted.

• To synchronize related components.

Answer explanation

The role of the data bus is to carry the actual binary data being transmitted, making it the correct choice among the options provided.

What does the control bus do?

• Carries the actual binary data.

• Performs arithmetic and logical operations.

• Carries command and control signals.

• Holds the address of the next instruction.

Answer explanation

The control bus carries command and control signals, not the actual binary data, arithmetic and logical operations, or the address of the next instruction.