Edexcel GCSE Computer Science (1CP2) exam questions

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Practice paper

4 questions · 15 marks

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1Short recall1 markPrimary Memory Swap Remove

Computers use RAM to store the data and instructions that are in use.

Name the term used to describe memory that loses its contents when the power is switched off.

[1 mark]

Mark scheme

Award one mark for:

Volatile (1)

Allow volatile memory / it is volatile.

Do not accept non-volatile, ROM, RAM or temporary/short term memory on their own, as these are not the term asked for.

Example answers and how they were marked

Full marks1/1

Volatile

Why: Correct term for memory that loses its contents when the power is switched off (1).

No marks0/1

Temporary memory

Why: Describes what such memory does but is not the term asked for; 'temporary memory' is on the Do not accept line, so no mark.

No marks0/1

Non-volatile

Why: Non-volatile memory keeps its contents when the power is switched off, the opposite of what the question describes; it is explicitly not accepted.

2Explain2 marksFetch Decode Execute Cycle Swap Remove

The control unit is part of the CPU.

Explain the role of the control unit in the fetch-decode-execute cycle.

[2 marks]

Mark scheme

Award up to two marks for a linked explanation such as:

Decodes/interprets/translates the instruction (1) to work out what the instruction is/what operation is required (1)
Sends control signals to the other components (1) so that the correct component carries out the instruction (1), e.g. the ALU/main memory
Controls the fetch of the instruction from main memory (1) because the address of the next instruction is sent via the address bus (1)
Controls the fetch of the next instruction from main memory (1) by sending a control signal/read signal to main memory (1)

For both marks, the expansion must follow/associate with the statement.

For the decode point, 'decodes the instruction' alone gains 1 mark; a second mark needs the purpose of decoding, i.e. working out what the instruction is/what operation is required.

Do not accept 'it controls the CPU' on its own, without naming a task in the cycle.

Do not accept 'it fetches the instruction from memory' on its own, as this describes the fetch step rather than the control unit's role; credit only if linked to controlling/signalling the fetch.

Do not accept carrying out arithmetic/logical operations, as these are carried out by the ALU, or holding the address of the next instruction, as this is the program counter.

Do not accept storing the instruction in a register (e.g. MAR/MDR), as this is not the role of the control unit.

Example answers and how they were marked

Full marks2/2

The control unit decodes each instruction, working out what it means, so that the CPU knows which component should carry it out.

Why: Linked point (1) and reason (1): decodes/interprets the instruction, and works out what it is/what operation is required.

Some marks1/2

It decodes the instruction that has been fetched from main memory.

Why: Decode point only (1); it does not explain the purpose of decoding, i.e. working out what the instruction is/what operation is required.

No marks0/2

It adds the two numbers together and stores the result in a register.

Why: Misconception: arithmetic is carried out by the ALU, which the mark scheme's Do not accept line covers.

3Discuss6 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.

4Discuss6 marksEmbedded Systems Swap Remove

A supermarket is replacing its staffed checkouts with self-service checkouts. Each checkout has a touchscreen, a barcode scanner and weighing scales. The supermarket wants the checkouts to be reliable and quick to respond.

Discuss why the supermarket should use embedded systems in its self-service checkouts rather than general-purpose computers.

Your answer should consider:

the characteristics of embedded systems
what self-service checkouts use embedded systems for
how embedded systems compare with general-purpose computers

You do not need to consider the cost of the materials used in the checkout.

[6 marks]

Mark scheme

Indicative content

Characteristics of embedded systems

An embedded system performs a single, dedicated task, so each self-service checkout is built only to scan, weigh and price items and cannot be used for any other job.
An embedded system has limited processing resources and storage, which is enough for the checkout to scan barcodes, weigh items and display prices.
An embedded system normally has a simple operating system held in ROM, so a checkout is less likely to fail while a customer is using it.
Embedded systems have low power consumption, so a row of checkouts can be left running all day without using much electricity.
Embedded systems are small and low cost per unit, so one can be built into each checkout unit and the supermarket can afford one at every till.
An embedded system has a limited user interface, so the checkout only shows its own screens to the customer.
The firmware of an embedded system is not normally changed by the customer, although a technician can update it when the supermarket changes the checkout's software.

Uses of embedded systems in the checkout

The checkout uses an embedded system to read the barcode scanner, so the correct price for each item is found quickly.
The checkout uses an embedded system to read the weighing scales, so the weight of the items can be checked against the product that was scanned.
The checkout uses an embedded system to control the touchscreen that shows the customer what to do and how much to pay.
The checkout uses an embedded system to respond quickly to each scan, because it only carries out the checkout's own tasks, which keeps the queues moving.
The checkout uses an embedded system so that it keeps working for long periods without being restarted, which means customers can use it without a member of staff.

Comparison with general-purpose computers

A general-purpose computer can run many different programs, whereas the checkout's embedded system runs one dedicated program, so it cannot be used for other jobs.
A general-purpose computer loads a full operating system when it starts and has other software running, so it can slow down or need restarting, whereas the checkout is not slowed down by other programs.
A general-purpose computer has far more processing power and memory than the checkout needs, so using one would be more expensive and would take up more space than an embedded system.
A general-purpose computer is designed for users to install new software, but the checkout's embedded system runs fixed firmware, so customers cannot change what the checkout does.

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)

Level 3 responses must consider both the characteristics of embedded systems and what the checkout uses them for, and must make a comparison with a general-purpose computer. Answers that only list characteristics or checkout tasks without linking them to the checkout are limited to Level 1.

Do not accept claims that embedded systems are faster than general-purpose computers or that they can run many different programs, as embedded systems have limited processing resources and carry out a single, dedicated task.

Example answers and how they were marked

Full marks6/6

An embedded system performs a single, dedicated task, so each self-service checkout is built only to scan items, weigh them and show prices. This suits the supermarket because the checkout does one job well instead of being used for anything else. The checkout uses its embedded system to read the barcode scanner, so the correct price is found quickly, and to read the weighing scales, so the weight of the items can be checked against the product that was scanned. It also controls the touchscreen that shows the customer what to do.

Embedded systems have limited processing resources and storage, which is more than enough for these tasks. Because they use a simple operating system held in ROM, they are less likely to fail while a customer is using them, so customers do not need a member of staff. They also have low power consumption, so a row of checkouts can run all day without using much electricity, and they are small and low cost per unit, so the supermarket can afford one at every till.

A general-purpose computer, by contrast, runs many programs and loads a full operating system, so it can slow down or need restarting and it is more expensive and bigger than the checkout needs. The embedded system runs fixed firmware, so customers cannot install software on the checkout, which keeps it reliable and quick to respond, and this is why it meets the supermarket's requirements better.

Why: Comprehensive understanding with sustained lines of reasoning: characteristics (single dedicated task, limited resources, simple operating system in ROM, low power, small and low cost) and uses (scanner, scales, touchscreen) are all applied to the checkout, and each is compared with a general-purpose computer. Meets the Level 3 guidance for a 6-mark answer.

Some marks2/6

Embedded systems are small and cheap. The checkout needs to scan items and weigh them. An embedded system can do this. It is reliable. A general-purpose computer could also do it but might crash more.

Why: Basic, independent points with little linkage or application: one characteristic (small and cheap), one use (scanning and weighing) and a brief comparison (a general-purpose computer might crash more). No line of reasoning is developed, so it is Level 1, top of the band, not Level 2.

No marks0/6

Embedded systems are better than normal computers because they are faster and can run lots of different programs. The checkout needs to be fast so it should use an embedded system.

Why: Level 0. Both claims are misconceptions that the mark scheme tells examiners not to accept (embedded systems have limited processing resources and run a single, dedicated program), and the last sentence only repeats the stem's requirement for quick responses, so there is no rewardable content.

Edexcel GCSE Computer Science (1CP2) Exam Questions

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2.1 Binary

2.2 Data representation

2.3 Data storage and compression

3.1 Hardware

3.2 Software

3.3 Programming languages

4.1 Networks

4.2 Network security

5.1 Environmental

5.2 Ethical and legal

5.3 Cybersecurity

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