Edexcel GCSE Computer Science (1CP2) Exam Questions

• A Desktop computer (1)
• The only correct answer is A. The correct answer is Desktop computer.
• B is not correct because a microwave oven uses an embedded system, built into it, to control a dedicated function
• C is not correct because a washing machine uses an embedded system, built into it, to control a dedicated function
• D is not correct because a traffic light uses an embedded system, built into it, to control a dedicated function

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.

Award one mark for any of the following up to a maximum of two marks:

• Decodes the instruction / works out what the instruction is (1)
• Sends control signals to the other components (of the CPU) (1)
• Coordinates/controls the activities of the CPU (1)
• Directs the timing of the other components / controls when each component acts (1)

Do not accept carrying out arithmetic or logical operations, as this is the role of the ALU.

Do not accept holding/storing the data or instructions, as this is the role of the registers/main memory.

Award one mark for any of the following up to a maximum of two marks:

• RAM can be accessed/read (much) faster than secondary storage / secondary storage is (much) slower than RAM (1)
• The CPU would have to wait/idle if instructions and data were read directly from secondary storage (1)
• The CPU can access RAM directly / RAM is directly accessible to the CPU (1)

Allow hard disk / hard drive / SSD for secondary storage.

Do not accept RAM is volatile / so that instructions and data are not lost when the power is switched off.

Do not accept the computer runs faster / has more storage (without reference to the CPU accessing instructions and data).

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

• The data and instructions held in RAM are lost/cleared/erased when the power is switched off / is cut (1) so RAM can only hold the data and instructions for programs that are currently running (1)
• If the power is switched off, the data and instructions held in RAM cannot be read/used by the CPU (1) so a program cannot carry on from where it stopped (1)
• RAM can only hold the data and instructions for a program while the computer is switched on (1) because it loses its contents / cannot keep them without a continuous power supply (1)

Accept 'RAM needs a continuous power supply' / 'RAM needs power to keep its data and instructions' as an alternative way of saying that the data and instructions in RAM are lost when the power is switched off (1). Do not award a second mark for a response that only repeats that the contents are lost when the power is switched off (e.g. 'the data is gone when the power is off').

Do not accept responses that say the data and instructions in RAM are permanent / are stored when the power is off.

Do not award a mark for responses that say RAM is temporary / temporarily holds data with no reference to the power being switched off.

Do not award a mark for responses that state data is deleted/lost without any reference to the power being switched off.

Do not award a mark for responses about RAM being fast, small/large in capacity or read-only, as these do not describe volatility.

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

• A temperature sensor measures/reads the temperature in the greenhouse (1) which the processor compares with the value stored in the system (1)
• The heater is switched on (1) when the temperature reading goes below the value stored in the system (1)
• A fan/vent/window is opened/a cooler is switched on (1) when the temperature reading goes above the value stored in the system (1)
• The temperature is checked/measured continuously (1) so the heater/fan is switched on or off as soon as the temperature changes (1)

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

Allow one mark for a correct point on its own without a linked reason, e.g. 'a temperature sensor measures the temperature'.

Do not award 'the embedded system controls/keeps the temperature correct' as this repeats the question.

Do not accept naming a device without saying what it does, e.g. 'the greenhouse has a thermostat'.

Award one mark for any of the following up to a maximum of three marks:

• The address (of the next instruction) is sent from the CPU to main memory / placed on the address bus (1)
• The (next) instruction is fetched/read from main memory (RAM) (1)
• The instruction is brought/copied into the CPU / received into the MDR (1)
• The program counter (PC) is incremented/updated to hold the address of the next instruction (1)

Allow 'the PC/MAR is placed on the address bus' for the address being sent to main memory.

Allow 'the MDR receives the instruction' for the instruction being brought into the CPU.

Do not award a second mark for the instruction being fetched from main memory and the instruction being brought into the CPU; these are the same point.

Do not award 'the instruction is transferred along the data bus' on its own; this is the same point as the instruction being fetched from main memory.

Do not accept answers about decoding the instruction, e.g. 'the instruction is fetched from RAM and decoded', as decoding happens in the decode stage.

Do not accept answers about the execute stage, e.g. 'the ALU carries out the calculation' or 'the result of a calculation is stored in a register', as these happen in the execute stage.

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.

Indicative content

Control unit and ALU

• The control unit fetches and decodes each instruction that the new computers are running, so it works out which operation has to be carried out.
• The control unit sends control signals to the ALU and to main memory over the control bus so that the other components carry out the instruction.
• The control unit receives the clock signal, so each stage of the cycle begins on a clock tick.
• The ALU carries out arithmetic operations, such as adding two values, and logical operations, such as comparing two values, during the execute stage.
• The ALU is the component that performs the calculations that a program running on the new computers needs.
• The data the ALU works on is held in registers, and the result of the operation is stored in a register such as the accumulator.

Registers

• Registers are small, very fast memory locations inside the CPU that hold the instructions and data the CPU is working on.
• The program counter holds the address of the next instruction to be fetched, and it is incremented each time an instruction is fetched.
• The memory address register (MAR) holds the address of the main memory location that is to be read from or written to during the fetch stage.
• The memory data register (MDR) holds the instruction or data brought from main memory (RAM) over the data bus before it is decoded.
• The accumulator holds the result of an operation carried out by the ALU.
• Because registers are inside the CPU, the CPU can keep working on a value without going back to slower main memory during the cycle.

Working together as the cycle repeats

• In the fetch stage, the address of the next instruction is copied from the program counter into the memory address register and sent to main memory over the address bus, and the instruction comes back over the data bus into the memory data register.
• In the decode stage the control unit interprets the instruction and works out which components are needed for it.
• In the execute stage the control unit signals the ALU or main memory so that the instruction is carried out, and the result is held in a register.
• The clock sends a regular pulse so that the fetch, decode and execute stages of each instruction happen in step.
• The program counter is then incremented, so the cycle repeats with the address of the next instruction to be fetched.

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

• A list of correct but independent roles, with no linkage between the components and no reference to the stages of the cycle, is limited to Level 1; an answer that gives the roles of the components but does not link them to the fetch, decode and execute stages is limited to Level 2; a Level 3 answer must cover the control unit/ALU and registers and link them to the stages of the cycle.
• Award no credit for 'the control unit is the brain of the CPU', 'the ALU stores data' or 'registers are the same as RAM'; accept the program counter, MAR, MDR and accumulator as examples of registers, accept the clock, address bus, data bus and control bus where they are linked to a stage of the cycle, and accept 'main memory' or 'RAM' as equivalent.

Indicative content

How data is stored on optical media

• Data is stored as pits and lands burnt or pressed into a spiral track on the disc.
• A laser beam is shone at the disc and the light that is reflected back is measured; pits and lands reflect the light differently.
• The differences in the reflected light are read as binary 1s and 0s.

Benefits of optical discs for selling films

• Optical discs are cheap to mass produce once the master disc has been pressed, so the studio can sell each film at a low price.
• A disc is small and light, so a customer can easily store it, carry it home or give it as a gift.
• A Blu-ray disc can hold a whole high-definition film (up to 50 GB), so a customer can watch the film without an internet connection.
• Artwork can be printed on the disc and its case, which helps the studio sell the film.

Drawbacks of optical discs for selling films

• A DVD holds only about 8.4 GB, so a high-definition film with extra features may not fit on one and the studio would need to sell it on a Blu-ray instead.
• Optical discs are easily scratched, which can cause read errors so the film will not play.
• Many modern devices, such as some laptops, no longer have a disc drive, so some customers would not be able to play the film.
• Discs can be affected by heat and sunlight, so they may deteriorate over time.

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 2 requires points to be linked or developed, for example a benefit or drawback explained in terms of the studio or its customers. An answer that only lists basic, independent points, with no linkage, is limited to Level 1.
• Level 3 requires all three areas and a judgement about whether the studio should keep selling films on optical discs. Do not credit magnetic storage or solid state storage as a description of how optical media stores data; credit these only where they are compared with optical media.