OCR A Level Computer Science Paper 1 (H446/01)
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1. What is the function of the Program Counter (PC)?
Answer:
The Program Counter (PC) stores the address of the next instruction to be
executed.
Rationale:
The PC is essential for controlling the sequence of execution. After each
instruction is fetched, the PC automatically updates to point to the next
instruction in memory. Without it, the CPU would not know where to continue
processing, making program execution impossible.
2. What is the role of the Current Instruction Register (CIR)?
Answer:
The CIR holds the instruction that is currently being decoded and executed.
Rationale:
Once an instruction is fetched from memory, it is placed into the CIR. The
control unit then decodes this instruction to determine what action to perform.
This step is critical in the fetch-decode-execute cycle, ensuring the CPU
correctly interprets commands.
,3. What does the Memory Address Register (MAR) do?
Answer:
The MAR stores the address of the memory location that the CPU wants to
access (read or write).
Rationale:
Whenever the CPU needs data, it must specify where that data is located. The
MAR acts as the “pointer” to that location, enabling accurate communication
with RAM. Without MAR, memory access would be disorganized and inefficient.
4. What is the function of the Memory Data Register (MDR)?
Answer:
The MDR temporarily stores data being transferred to or from memory.
Rationale:
The MDR acts as a buffer between the CPU and memory. When data is fetched, it
first goes into the MDR before being processed. Similarly, when data is written
to memory, it passes through the MDR. This buffering ensures smooth and
synchronized data transfer.
5. What is the role of the Arithmetic and Logic Unit (ALU)?
Answer:
The ALU performs all arithmetic calculations and logical operations.
Rationale:
The ALU is the “thinking” part of the CPU. It handles operations such as
addition, subtraction, comparisons (greater than, equal to), and logical
decisions. Every computation in a program ultimately passes through the ALU.
6. What is the function of the Accumulator?
Answer:
The accumulator temporarily stores intermediate results during processing.
Rationale:
During calculations, results are often needed for further operations. The
,accumulator holds these intermediate values so they can be reused without
going back to memory, improving efficiency and speed.
7. What is RISC (Reduced Instruction Set Computer)?
Answer:
RISC is a CPU architecture that uses a small set of simple instructions, each
executed in one clock cycle.
Rationale:
RISC simplifies processing by breaking tasks into smaller steps. This allows for
pipelining, where multiple instructions are processed simultaneously at different
stages. Although it requires more RAM and compiler effort, it results in faster
execution overall.
8. What are the advantages and disadvantages of RISC?
Answer:
Advantages:
• Faster execution due to simple instructions
• Supports pipelining
• Efficient performance
Disadvantages:
• Requires more RAM
• Compiler must do more work
Rationale:
RISC shifts complexity from hardware to software. This makes hardware faster
but increases reliance on efficient programming.
9. What is CISC (Complex Instruction Set Computer)?
Answer:
CISC is a CPU architecture with a large set of complex instructions that can
perform multiple operations in one command.
, Rationale:
CISC reduces the number of instructions per program by combining tasks.
However, many of these instructions are rarely used, making the system less
efficient overall compared to RISC.
10. What are the advantages and disadvantages of CISC?
Answer:
Advantages:
• Requires fewer lines of code
• Less work for the compiler
• Lower RAM usage
Disadvantages:
• Slower execution
• Inefficient use of instruction set
Rationale:
CISC prioritizes convenience over speed, which can slow down processing
compared to streamlined RISC systems.
11. What is a GPU (Graphics Processing Unit)?
Answer:
A GPU is a specialized processor designed to render images and graphics.
Rationale:
Unlike the CPU, which handles general tasks, the GPU is optimized for parallel
processing, making it ideal for graphics, gaming, video rendering, and AI
workloads.
12. What is a Multi-core CPU?
Answer:
A multi-core CPU contains multiple processing cores on a single chip.
Rationale:
Each core can execute instructions independently, enabling parallel processing.
| High-Yield Practice Questions, Algorithms,
Programming & Comprehensive Revision Guide|
Graded A+ , Well Rationalized ,Updated and
Reviewed | Latest Exam and Newest Updated
Version!!!!
1. What is the function of the Program Counter (PC)?
Answer:
The Program Counter (PC) stores the address of the next instruction to be
executed.
Rationale:
The PC is essential for controlling the sequence of execution. After each
instruction is fetched, the PC automatically updates to point to the next
instruction in memory. Without it, the CPU would not know where to continue
processing, making program execution impossible.
2. What is the role of the Current Instruction Register (CIR)?
Answer:
The CIR holds the instruction that is currently being decoded and executed.
Rationale:
Once an instruction is fetched from memory, it is placed into the CIR. The
control unit then decodes this instruction to determine what action to perform.
This step is critical in the fetch-decode-execute cycle, ensuring the CPU
correctly interprets commands.
,3. What does the Memory Address Register (MAR) do?
Answer:
The MAR stores the address of the memory location that the CPU wants to
access (read or write).
Rationale:
Whenever the CPU needs data, it must specify where that data is located. The
MAR acts as the “pointer” to that location, enabling accurate communication
with RAM. Without MAR, memory access would be disorganized and inefficient.
4. What is the function of the Memory Data Register (MDR)?
Answer:
The MDR temporarily stores data being transferred to or from memory.
Rationale:
The MDR acts as a buffer between the CPU and memory. When data is fetched, it
first goes into the MDR before being processed. Similarly, when data is written
to memory, it passes through the MDR. This buffering ensures smooth and
synchronized data transfer.
5. What is the role of the Arithmetic and Logic Unit (ALU)?
Answer:
The ALU performs all arithmetic calculations and logical operations.
Rationale:
The ALU is the “thinking” part of the CPU. It handles operations such as
addition, subtraction, comparisons (greater than, equal to), and logical
decisions. Every computation in a program ultimately passes through the ALU.
6. What is the function of the Accumulator?
Answer:
The accumulator temporarily stores intermediate results during processing.
Rationale:
During calculations, results are often needed for further operations. The
,accumulator holds these intermediate values so they can be reused without
going back to memory, improving efficiency and speed.
7. What is RISC (Reduced Instruction Set Computer)?
Answer:
RISC is a CPU architecture that uses a small set of simple instructions, each
executed in one clock cycle.
Rationale:
RISC simplifies processing by breaking tasks into smaller steps. This allows for
pipelining, where multiple instructions are processed simultaneously at different
stages. Although it requires more RAM and compiler effort, it results in faster
execution overall.
8. What are the advantages and disadvantages of RISC?
Answer:
Advantages:
• Faster execution due to simple instructions
• Supports pipelining
• Efficient performance
Disadvantages:
• Requires more RAM
• Compiler must do more work
Rationale:
RISC shifts complexity from hardware to software. This makes hardware faster
but increases reliance on efficient programming.
9. What is CISC (Complex Instruction Set Computer)?
Answer:
CISC is a CPU architecture with a large set of complex instructions that can
perform multiple operations in one command.
, Rationale:
CISC reduces the number of instructions per program by combining tasks.
However, many of these instructions are rarely used, making the system less
efficient overall compared to RISC.
10. What are the advantages and disadvantages of CISC?
Answer:
Advantages:
• Requires fewer lines of code
• Less work for the compiler
• Lower RAM usage
Disadvantages:
• Slower execution
• Inefficient use of instruction set
Rationale:
CISC prioritizes convenience over speed, which can slow down processing
compared to streamlined RISC systems.
11. What is a GPU (Graphics Processing Unit)?
Answer:
A GPU is a specialized processor designed to render images and graphics.
Rationale:
Unlike the CPU, which handles general tasks, the GPU is optimized for parallel
processing, making it ideal for graphics, gaming, video rendering, and AI
workloads.
12. What is a Multi-core CPU?
Answer:
A multi-core CPU contains multiple processing cores on a single chip.
Rationale:
Each core can execute instructions independently, enabling parallel processing.
