Edexcel GCSE Computer Science (1CP2) Exam Questions

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

• Decodes each (fetched) instruction (1) to work out which operation is needed / which components should carry it out (1)
• Coordinates/directs the other components (1) by sending control signals along the control bus (1)
• Fetches the next instruction (1) by sending its address to main memory along the address bus (1)
• Sends a read/write control signal to main memory (1) so that the instruction or data is transferred during the fetch/execute stage (1)

Do not accept answers about synchronising the CPU or timing the cycles (that is the role of the clock).

Do not accept answers about carrying out arithmetic or logical operations (that is the ALU).

Do not accept answers about holding data or the results of instructions (that is registers/main memory).

Do not accept generic answers that only say the CU controls the CPU or processes instructions, with no linked development.

Only award one mark for a response that only repeats that the CU sends control signals; the second mark needs a linked outcome such as coordination, a memory read/write, or fetching an instruction.

Do not accept 'during the decode stage' as the development for the decoding point, as it restates the question.

Indicative content

Magnetic storage

• A magnetic hard disk drive stores data on a magnetic platter that spins, with a read/write head on an actuator arm that moves over its surface.
• The read/write head magnetises small areas of the platter to represent binary 1s and 0s, and reads the magnetic pattern back when the data is needed.
• The data is held on concentric tracks that are divided into sectors. (Accept data being stored magnetically without further detail, but a vague 'it uses a magnet' is not enough for this point.)
• The platter and the read/write head are sealed inside the drive unit because of the precision needed.

Solid state storage

• A solid state drive stores data in flash memory chips and has no moving parts.
• A large electric current forces electrons through a barrier and traps them in a floating gate; the presence or absence of this trapped charge represents a 1 or a 0. (Accept either convention for which charge state represents a 1 and which represents a 0.)
• The charged cells are detected to read the data back. (Accept: the data can be erased and rewritten by applying a new current.)
• As there is no disk to spin to the correct position and no arm to move, data can be read from and written to solid state storage very quickly.

Suitability for the company's video files

• A magnetic HDD has a very large capacity and is generally cheaper per gigabyte than an SSD of the same capacity, which suits a company that stores many large video files.
• An SSD has very fast read/write speeds, so the company's large video files open and save quickly while they are being edited.
• An SSD has no moving parts, so it is more durable if the company's computers are carried between filming locations.
• A magnetic HDD could store finished videos as an archive and an SSD could hold the project being edited, so the company gets high speed while editing and low-cost capacity for storage.

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 answers must give accurate accounts of how data is stored on both magnetic and solid state storage and sustain a line of reasoning that applies at least one of them to the company's video files. An answer that covers only one storage type, or that describes both types without any application to the company, cannot go above Level 2.
• Do not accept descriptions of optical storage (pits and lands, a laser) as magnetic or solid state storage, and do not accept 'magnetic storage uses a laser' or 'solid state storage is volatile' or 'solid state storage is RAM'.

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.