Which one of the statements shown below about the control unit is true?

Question

BlackTom AI · Accepted Answer

The control unit manages the flow of electrical control signals throughout the CPU, so the correct statement is: the control unit receives and sends electrical signals.

1) Relevant knowledge points and concepts
- The CPU is organized around a control unit (CU), arithmetic/logic unit (ALU), registers, and memory.  
- The CU implements the fetch–decode–execute cycle by issuing control signals and reading status signals.  
- These signals are digital electrical pulses sent over buses and control lines; program storage is handled by memory (RAM/ROM), not by the CU itself.

2) Step-by-step reasoning process
- Fetch: The CU issues address and read signals to memory to fetch the next instruction (CU sends electrical signals).  
- Decode: The CU decodes the fetched instruction internally and determines which components must act (internal logic and control registers).  
- Execute: The CU sends specific control signals to the ALU, registers, and I/O devices to perform the operation (CU sends electrical signals).  
- Status/Feedback: Devices and the ALU return status flags and data to the CU so it can update the program counter or handle interrupts (CU receives electrical signals).  
Because the CU both initiates actions and monitors responses, it both sends and receives electrical signals.

3) Intermediate steps / interactions (explicit)
- CU sends memory address and read command → memory returns instruction (receive).  
- CU decodes → CU sends control lines to ALU and registers (send).  
- ALU performs operation → ALU sets status flags that CU reads (receive).  
- CU updates PC and issues next fetch (send).

4) Why the correct answer is correct
- The CU’s role requires bidirectional electrical communication: sending control lines to coordinate hardware, and receiving data/status to make decisions. Control is implemented with digital electrical signals, not analogue, and the CU does not permanently store programs.

5) Why the other options are incorrect
- (a) Incorrect: permanent program storage is the role of memory (ROM/RAM), not the CU.  
- (b) Incorrect: the CU sends digital electrical control signals, not analogue signals.  
- (c) Incorrect: the CU does not only receive signals; it actively sends control signals as well.

6) Conclusion
This confirms option d. "The control unit receives and sends electrical signals."

Which one of the statements shown below about the control unit is true?单项选择题

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