Edexcel GCSE Computer Science (1CP2) Exam Questions

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

• A read/write head moves over the surface of the disk (1) to read/write data by detecting or changing the magnetic alignment of areas of the surface (1)
• The head magnetises areas of the disk surface in different directions (1) so each area represents a binary 1 or 0 (1)
• Data is stored on concentric circles called tracks (1) which are divided into sectors (1)

Allow one mark for tracks/concentric circles on their own.

For the second mark in the first two bullets, the response must refer to the magnetic alignment/charge being detected or changed, not just that the head reads/writes data.

Do not award a mark for 'it is magnetic' or 'it stores data in binary' with no description of how the data is stored.

Do not accept descriptions of optical storage (e.g. a laser, pits and lands) or solid state storage (e.g. electric charges in chips).

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

• The address bus carries the address of the next instruction (1) so the CPU can locate/fetch it from main memory/RAM (1)
• The address bus carries the address of the memory location to be read (1) so the instruction/data stored there can be located/accessed (1)
• The CPU needs to know where the next instruction is stored (1) so the address bus sends the address to main memory/RAM (1)

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

Allow 'from the program counter/PC' as part of the point for one mark, e.g. the address bus carries the address from the program counter (1), but the second mark needs the destination or purpose (e.g. to locate/fetch the instruction in main memory/RAM).

Do not award the second mark for naming the program counter/PC alone.

Do not accept answers that say the address bus carries data/instructions from main memory to the CPU, as these travel on the data bus.

Do not accept answers that say the address bus stores the address.

Do not allow an answer that only restates that the address bus carries addresses without saying which address or why it is needed.

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.

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.