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Edexcel GCSE Computer Science (1CP2) Exam Questions

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3 questions · 13 marks

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1Multiple choice1 markStored Program Computers Swap Remove

Identify the function of the control unit in the fetch-decode-execute cycle.

[1 mark]
  • ADecodes instructions
  • BPerforms arithmetic operations
  • CStores data and instructions
  • DTemporarily stores data being processed
Mark scheme
  • A Decodes instructions (1)
  • The only correct answer is A. The correct answer is Decodes instructions.
  • B is not correct because the arithmetic logic unit performs arithmetic operations
  • C is not correct because main memory stores data and instructions
  • D is not correct because registers temporarily store data being processed
Example answers and how they were marked
Full marks1/1

A Decodes instructions

Why: Correct option: the control unit decodes instructions during the fetch-decode-execute cycle (1).

No marks0/1

C Stores data and instructions

Why: Main memory stores data and instructions, not the control unit; this is a common distractor, so no mark.

No marks0/1

B Performs arithmetic operations

Why: Arithmetic operations are performed by the ALU, not the control unit; a common confusion between CPU components, so no mark.

2Discuss6 marksFetch Decode Execute Cycle Swap Remove

A small robotics company is designing a new robot. The robot's computer uses von Neumann architecture. The engineers are explaining how programs are stored and run.

Discuss how the von Neumann stored program concept and main memory (RAM) are used during the fetch-decode-execute cycle.

Your answer should include:

  • what is meant by the stored program concept
  • the role of RAM in the cycle
  • why the stored program concept is useful.
[6 marks]
Mark scheme

Indicative content

Stored program concept

  • Instructions and data are stored together in the same main memory (RAM).
  • Instructions are fetched one at a time from memory and executed in sequence.
  • The program can be changed by loading different instructions into RAM.
  • The CPU can only execute instructions that are in main memory.

Role of RAM

  • RAM holds the program instructions and the data being used.
  • The address of the next instruction is held in the program counter (PC).
  • The instruction is fetched from RAM using the address bus.
  • The data bus carries the instruction from RAM to the CPU.
  • RAM is volatile, so programs are lost when power is off.
  • RAM is directly accessible by the CPU, unlike secondary storage.

Benefits

  • The same hardware can run many different programs.
  • Programs can be loaded and changed quickly.
  • No need to rewire the computer for a new task.
  • Makes general-purpose computers possible.

Levels

  • Level 0 (0 marks): No rewardable content.
  • Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
  • Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
  • Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)
Example answers and how they were marked
Full marks6/6

The von Neumann stored program concept means that both the program instructions and the data are stored together in the same main memory, RAM. During the fetch-decode-execute cycle, the CPU fetches an instruction from RAM, decodes it in the control unit, and then executes it. The program counter holds the address of the next instruction, and this address is sent along the address bus to RAM. RAM then returns the instruction along the data bus to the CPU. RAM is volatile, so it only holds the program while the robot is powered on. The stored program concept is useful because the robot's computer can run different programs without changing any hardware; new instructions can simply be loaded into RAM. This makes the computer general-purpose and flexible.

Why: Comprehensive understanding: defines stored program concept, explains RAM role with PC, address bus and data bus, applies to robot, and gives benefits. Sustained lines of reasoning. Level 3.

Some marks3/6

The stored program concept is when instructions and data are stored in RAM. The CPU fetches instructions from RAM. The program counter keeps the address of the next instruction. RAM holds the program. The benefit is that you can change the program without rewiring the computer.

Why: Adequate understanding: correct basic points about stored program concept and RAM, with some linkage, but little development or application to the robot's fetch-decode-execute cycle. Level 2.

Some marks1/6

The von Neumann stored program concept is that the CPU uses RAM to store the program. The fetch-decode-execute cycle fetches, decodes and executes. RAM is random access memory. The benefit is that it is fast.

Why: Basic independent points only; no real linkage or application to the robot. Level 1.

3Discuss6 marksPrimary Memory Swap Remove

A school is buying new computers for its IT room. The computers the technician has ordered have 16 GB of RAM and a large hard drive.

Discuss why main memory (RAM) is needed for programs to run on these computers.

Your answer should include:

  • the role of RAM in the stored program concept
  • what happens to a program when it is opened
  • why the CPU cannot execute a program directly from secondary storage.
[6 marks]
Mark scheme

Indicative content

the role of RAM in the stored program concept

  • In the von Neumann stored program concept, a program's instructions and the data it uses are held together in main memory.
  • RAM holds the instructions and data of the program that the CPU is currently processing.
  • The CPU fetches each instruction from RAM during the fetch-decode-execute cycle, so a program must be in RAM before it can be run.
  • RAM is directly accessible by the CPU, so instructions can be fetched quickly enough for the CPU to keep working.

what happens to a program when it is opened

  • When a program is opened, a copy of its instructions and data is transferred from secondary storage, such as the hard drive, into RAM.
  • The operating system loads the program into RAM so that the CPU can start fetching and executing its instructions.
  • When the program is closed, it is removed from RAM, and the space it used is free for another program.
  • If a computer does not have enough RAM, the program may not open, or another open program has to be closed first.

why the CPU cannot execute a program directly from secondary storage

  • Secondary storage, such as a hard disk drive, is much slower to access than RAM.
  • The CPU can process instructions much faster than secondary storage can supply them, so the CPU would have to wait and would not be working at full speed.
  • RAM is fast electronic memory with no moving parts, so data can be read from it in a fraction of the time taken by a magnetic hard disk drive.
  • Running the school's programs directly from secondary storage would make the computers in the IT room very slow to use.

Levels

  • Level 0 (0 marks): No rewardable content.
  • Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
  • Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
  • Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)

Additional guidance

  • Level 3 responses must cover both the role of RAM in the stored program concept and the speed difference between RAM and secondary storage, with a reason such as the CPU having to wait for instructions.
  • Answers that make only basic, independent points, such as what RAM is, that a program is copied into RAM when it is opened, or that RAM is faster than a hard drive, without linking them to explain why the CPU would have to wait for instructions, are limited to Level 1.
  • Do not accept statements that RAM is permanent storage, that RAM replaces secondary storage, or that secondary storage is read-only.
Example answers and how they were marked
Full marks6/6

The computers need RAM because of the von Neumann stored program concept, in which the instructions of a program and the data it uses are both held in main memory. When a student opens a program on one of the new computers, the operating system copies it from the hard drive into RAM. The CPU then fetches each instruction from RAM in the fetch-decode-execute cycle, so the program must be in RAM before it can be run. The CPU cannot execute a program directly from secondary storage because a hard disk drive is much slower than RAM. It has moving parts and a much lower transfer rate, so the CPU would often have nothing to do while it waited for the next instruction. RAM is fast electronic memory that the CPU can read directly, which is why 16 GB of RAM lets the school run several programs at once and still keep the CPU working at full speed.

Why: Comprehensive understanding: the stored program concept is explained (instructions and data held in main memory), the program being opened is linked to it, and the speed difference is developed with the reason that the CPU would wait for instructions, all applied to the school's computers. Level 3.

Some marks2/6

RAM is the main memory of the computer. It stores the programs and data that are being used at the moment. When you open a program it is copied into RAM, and the CPU fetches instructions from RAM. RAM is faster than the hard drive, so a program runs better from RAM. Having 16 GB means the school can have more programs open at once.

Why: Basic, independent points only: what RAM is, that a program is copied into RAM when it is opened, that the CPU fetches instructions from RAM, and that RAM is faster than a hard drive. None is linked to the stored program concept or developed to explain why the CPU would have to wait for instructions, so Level 1, 2 marks.

No marks0/6

RAM is the permanent storage inside the computer, like a hard drive. The school needs 16 GB of RAM so that all the students' files can be saved permanently. When a program is opened, it is copied from RAM to the CPU. The CPU cannot execute from secondary storage because secondary storage is read-only.

Why: No creditworthy points. RAM is described as permanent storage, files are said to be saved permanently in RAM, a program is said to be copied from RAM to the CPU, and secondary storage is said to be read-only. All are the misconceptions listed in the Do not accept guidance, so Level 0.

Questions by topic

2.1 Binary

Build a paper on this topic 58
Adding Binary Numbers 6 questions Binary and Hexadecimal Basics 10 questions Binary Shifts 6 questions Binary to Denary Conversion 6 questions Binary to Hexadecimal Conversion 6 questions Denary to Binary Conversion 6 questions Denary to Hexadecimal Conversion 6 questions Denary to Negative Binary Conversion 6 questions Hexadecimal to Binary Conversion 6 questions

2.2 Data representation

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Character Sets 18 questions Images 19 questions Sound 19 questions

2.3 Data storage and compression

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Compression 18 questions Units & Conversion 6 questions

3.1 Hardware

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Embedded Systems 17 questions Fetch Decode Execute Cycle 15 questions Primary Memory 15 questions Secondary Memory 15 questions Stored Program Computers 15 questions

3.2 Software

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File Management 18 questions Memory Management 16 questions Peripheral Management 11 questions Process Management 12 questions Purpose & Function of Operating Systems 17 questions Software Basics 13 questions User Management 18 questions Utility Software 19 questions

3.3 Programming languages

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Low and High Level Languages 19 questions Translators 18 questions

4.1 Networks

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Addressing 16 questions LANs & WANs 16 questions Network Speed 5 questions Packet Switching 16 questions Protocols & Layers 17 questions The Internet 16 questions Topologies 17 questions Wired Connections 17 questions Wireless Connections 18 questions

4.2 Network security

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Network Security Risks 18 questions Preventing Network Security Risks 18 questions

5.1 Environmental

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E-waste 17 questions Manufacturing Technology 19 questions

5.2 Ethical and legal

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Data Protection Act 17 questions Impact of AI 18 questions Intellectual Property 18 questions Software Licences 18 questions

5.3 Cybersecurity

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Malware 18 questions Social Engineering 18 questions

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