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.

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

• It controls the motors/rotors (1) so that the drone can take off, hover, turn and land (1)
• It keeps the drone stable/level automatically (1) by taking readings from a sensor (accelerometer/gyroscope/GPS) (1)
• It receives signals from the remote control (1) and changes the speed of the motors to steer the drone (1)
• It monitors the battery level (1) and brings the drone back to the ground before the battery runs out (1)

The development must relate to the function given in the point.

Accept a named function that the embedded system controls, e.g. 'it keeps the drone level', as the first mark (1).

Award the second mark only when the development gives a specific outcome or detail of that function, e.g. 'so that the drone can take off, hover, turn and land' or 'by changing the motor speeds to keep it level'.

Do not award the second mark for a generic outcome such as 'so it works', 'so it can fly' or 'so the drone moves'.

A bare 'it controls the motors so it can fly' therefore earns the first mark only.

Allow any other specific function of a drone that is carried out by the embedded system.

Do not accept 'it flies the drone' / 'it is the drone's brain' / 'it makes the drone work' without a named function being controlled.

Do not accept answers that describe the user or the remote control flying the drone with no function carried out by the embedded system.

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 up to two marks for a linked explanation such as:

• The CPU can only fetch/read instructions from main memory/RAM (1) so the instructions of a running program must be copied/loaded into RAM before they can be executed (1)
• RAM is faster to access than secondary storage (1) so the instructions can be fetched quickly enough for the CPU to execute them (1)
• The CPU needs the instructions in RAM to fetch and execute them (1) because the fetch-decode-execute cycle reads each instruction from main memory/RAM (1)
• The address of the next instruction is sent to RAM on the address bus (1) so the instruction can be transferred to the CPU/registers for decoding/execution (1)

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

Allow the point and reason in either order if they are linked.

Do not accept answers that only say the CPU needs instructions, or that RAM is faster, without linking this to fetching/executing the instructions.

Do not accept answers that only say RAM holds data and instructions without linking this to the fetch-decode-execute cycle.

Do not accept 'RAM is permanent/non-volatile storage, so the instructions are kept safe' - RAM is volatile.

The response does not need to name the address bus or the fetch stage for full marks; a linked reason that explains why instructions must be in RAM (for example, the CPU can only fetch from RAM, or RAM is faster than secondary storage) is enough.