OCR EXAM COMPLETE STUDY GUIDE
NEWEST 2026 | OCR TEST BANK |
PRACTICE QUESTIONS AND
DETAILED RATIONALES |2026
EDITION
Question: What does the Arithmetic Logic Unit (ALU) do?
A) Coordinates activities of the CPU
B) Stores the results of calculations
C) Performs operations on data such as addition and subtraction
D) Holds the memory address of the instruction for each cycle
Correct Answer: C Performs operations on data such as addition and subtraction
Expert Rationale: The ALU is the component of the CPU responsible for performing
arithmetic and logical operations. Understanding this is essential because the ALU
executes all mathematical calculations and logical comparisons. Without the ALU, the
CPU could not process data.
Question: What is the function of the Control Unit (CU)?
A) Performs arithmetic operations
B) Coordinates the activities of the CPU
C) Stores frequently used data
D) Holds the actual data or instruction
Correct Answer: B Coordinates the activities of the CPU
Expert Rationale: The Control Unit directs the operation of the processor by coordinating
the activities of the CPU. Understanding this is essential because the CU manages the
fetch-decode-execute cycle and controls the flow of data within the CPU. It acts as the
"traffic controller" of the processor.
,Question: What are registers?
A) Collection of wires that carry signals between components
B) Quick, small stores of data within the CPU
C) Memory that stores frequently used data
D) A type of non-volatile memory
Correct Answer: B Quick, small stores of data within the CPU
Expert Rationale: Registers are small, high-speed storage locations within the CPU.
Understanding this is essential because registers hold data and instructions temporarily
during processing. They are the fastest type of memory in a computer system.
Question: What does the Memory Address Register (MAR) hold?
A) The actual data or instruction
B) The results of calculations
C) The memory address for data or an instruction about to be used by the CPU
D) The memory address of the instruction for each cycle
Correct Answer: C The memory address for data or an instruction about to be used by the
CPU
Expert Rationale: The MAR holds the address of the memory location that the CPU needs
to access. Understanding this is essential because the MAR identifies where data or
instructions are stored in memory. Without the MAR, the CPU could not locate the correct
memory location.
Question: What does the Memory Data Register (MDR) hold?
A) The memory address for data
B) The actual data or instruction
C) The results of calculations
D) The memory address of the instruction for each cycle
Correct Answer: B The actual data or instruction
Expert Rationale: The MDR holds the actual data or instruction fetched from or written to
memory. Understanding this is essential because the MDR temporarily stores the data
, being transferred between the CPU and memory. It acts as a buffer for data being read or
written.
Question: What is the function of the Accumulator?
A) Holds memory address for data
B) Performs arithmetic operations
C) Stores results of calculations in the ALU
D) Holds memory address of the instruction for each cycle
Correct Answer: C Stores results of calculations in the ALU
Expert Rationale: The Accumulator is a register that stores intermediate results from the
ALU. Understanding this is essential because the accumulator holds the result of
arithmetic and logic operations. It is a key register in the CPU's processing pipeline.
Question: What does the Program Counter (PC) do?
A) Holds the actual data or instruction
B) Stores the results of calculations
C) Holds the memory address of the instruction for each cycle
D) Coordinates the activities of the CPU
Correct Answer: C Holds the memory address of the instruction for each cycle
Expert Rationale: The Program Counter holds the address of the next instruction to be
executed. Understanding this is essential because the PC controls the flow of the fetch-
decode-execute cycle. The PC is incremented after each instruction fetch.
Question: What is the Fetch stage of the fetch-decode-execute cycle?
A) The CPU performs what the instructions told
B) The instruction is broken down and decoded
C) The next instruction is retrieved by the CPU from main memory
D) The CPU coordinates its activities
Correct Answer: C The next instruction is retrieved by the CPU from main memory
Expert Rationale: The Fetch stage retrieves the next instruction from memory.
Understanding this is essential because the fetch stage is the first step in processing
NEWEST 2026 | OCR TEST BANK |
PRACTICE QUESTIONS AND
DETAILED RATIONALES |2026
EDITION
Question: What does the Arithmetic Logic Unit (ALU) do?
A) Coordinates activities of the CPU
B) Stores the results of calculations
C) Performs operations on data such as addition and subtraction
D) Holds the memory address of the instruction for each cycle
Correct Answer: C Performs operations on data such as addition and subtraction
Expert Rationale: The ALU is the component of the CPU responsible for performing
arithmetic and logical operations. Understanding this is essential because the ALU
executes all mathematical calculations and logical comparisons. Without the ALU, the
CPU could not process data.
Question: What is the function of the Control Unit (CU)?
A) Performs arithmetic operations
B) Coordinates the activities of the CPU
C) Stores frequently used data
D) Holds the actual data or instruction
Correct Answer: B Coordinates the activities of the CPU
Expert Rationale: The Control Unit directs the operation of the processor by coordinating
the activities of the CPU. Understanding this is essential because the CU manages the
fetch-decode-execute cycle and controls the flow of data within the CPU. It acts as the
"traffic controller" of the processor.
,Question: What are registers?
A) Collection of wires that carry signals between components
B) Quick, small stores of data within the CPU
C) Memory that stores frequently used data
D) A type of non-volatile memory
Correct Answer: B Quick, small stores of data within the CPU
Expert Rationale: Registers are small, high-speed storage locations within the CPU.
Understanding this is essential because registers hold data and instructions temporarily
during processing. They are the fastest type of memory in a computer system.
Question: What does the Memory Address Register (MAR) hold?
A) The actual data or instruction
B) The results of calculations
C) The memory address for data or an instruction about to be used by the CPU
D) The memory address of the instruction for each cycle
Correct Answer: C The memory address for data or an instruction about to be used by the
CPU
Expert Rationale: The MAR holds the address of the memory location that the CPU needs
to access. Understanding this is essential because the MAR identifies where data or
instructions are stored in memory. Without the MAR, the CPU could not locate the correct
memory location.
Question: What does the Memory Data Register (MDR) hold?
A) The memory address for data
B) The actual data or instruction
C) The results of calculations
D) The memory address of the instruction for each cycle
Correct Answer: B The actual data or instruction
Expert Rationale: The MDR holds the actual data or instruction fetched from or written to
memory. Understanding this is essential because the MDR temporarily stores the data
, being transferred between the CPU and memory. It acts as a buffer for data being read or
written.
Question: What is the function of the Accumulator?
A) Holds memory address for data
B) Performs arithmetic operations
C) Stores results of calculations in the ALU
D) Holds memory address of the instruction for each cycle
Correct Answer: C Stores results of calculations in the ALU
Expert Rationale: The Accumulator is a register that stores intermediate results from the
ALU. Understanding this is essential because the accumulator holds the result of
arithmetic and logic operations. It is a key register in the CPU's processing pipeline.
Question: What does the Program Counter (PC) do?
A) Holds the actual data or instruction
B) Stores the results of calculations
C) Holds the memory address of the instruction for each cycle
D) Coordinates the activities of the CPU
Correct Answer: C Holds the memory address of the instruction for each cycle
Expert Rationale: The Program Counter holds the address of the next instruction to be
executed. Understanding this is essential because the PC controls the flow of the fetch-
decode-execute cycle. The PC is incremented after each instruction fetch.
Question: What is the Fetch stage of the fetch-decode-execute cycle?
A) The CPU performs what the instructions told
B) The instruction is broken down and decoded
C) The next instruction is retrieved by the CPU from main memory
D) The CPU coordinates its activities
Correct Answer: C The next instruction is retrieved by the CPU from main memory
Expert Rationale: The Fetch stage retrieves the next instruction from memory.
Understanding this is essential because the fetch stage is the first step in processing
