Edexcel GCSE Computer Science (1CP2) Exam Questions

• A They are lost (1)
• The only correct answer is A. The correct answer is They are lost
• B is not correct because RAM is volatile and its contents are lost when the power is switched off, so they are not stored permanently
• C is not correct because RAM is volatile and its contents are lost when the power is switched off, so they are not saved to secondary storage
• D is not correct because ROM is read-only memory that holds the start-up instructions, so the contents of RAM are not written to it

Award one mark for:

• Embedded (computer) system (1)

Allow embedded computer/embedded device.

Allow dedicated (computer) system.

Do not accept microcontroller/microprocessor controlled system.

Do not accept general purpose computer/PC/laptop.

Award one mark for:

• Laser (1)

Allow laser beam

Do not accept read/write head

Do not accept pits

Do not accept lands

Do not accept reflective surface

Do not accept magnet/magnetic

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:

• 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:

• Data is stored as electric charges (1) which are trapped/held in the memory cells/chips (1)
• A current forces electrons through a barrier (1) and they stay trapped on the other side until another current/'flash' is applied (1)
• A cell that is holding trapped electrons/a charge represents a 1 (1) and a cell with no charge represents a 0 (1)

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

Allow one mark for stating that data is stored as electric charges/electrons without a linked reason.

Do not accept 'there are no moving parts' or 'it is fast/durable' - these are characteristics of solid state storage, not how data is stored.

Do not accept 'data is stored magnetically' or 'as pits and lands'.

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

• It decodes instructions (1) so the CPU knows what operation/instruction to perform (1)
• It sends control signals (1) to coordinate/control the flow of data/instructions between components (1)
• It manages/directs the fetch-decode-execute cycle (1) by controlling the sequence/timing of the stages (1)
• It directs the other components of the CPU (1) so that each instruction is fetched/decoded/executed in the correct order (1)

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

Allow an explanation that the control unit directs data/instructions along the address/data/control buses (1) so the fetch-decode-execute cycle can take place (1)

Do not accept a generic 'it controls the CPU/components' point without linked expansion as to what is controlled/directed.

Do not accept 'it fetches instructions from memory' on its own; credit only if linked to the address/data/control buses or control signals.

Do not accept 'it stores/holds the instruction/data' as this is the role of a register.

Do not accept answers about the ALU performing calculations.

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

• Control unit / CU (1)
• Arithmetic logic unit / ALU (1)
• Register(s) (1)
• Clock (1)

Do not accept main memory / RAM.

Do not accept cache.

Marks can be awarded in any order.

Indicative content

The role of the CPU and registers

• The control unit decodes the instruction fetched from main memory and controls the other components during the cycle.
• The ALU carries out arithmetic and logical operations during the execute stage, such as adding two values held in registers.
• Registers hold the data, addresses and results that the CPU is working on during the cycle.
• The program counter holds the address of the next instruction to be fetched, so it is incremented after each fetch.
• The memory address register holds the address of the memory location that is about to be read or written.
• The memory data register holds the instruction or data that has been fetched from or is being written to main memory.

The role of the address bus, data bus and control bus

• The address bus carries the address of the memory location that the CPU needs to access from the CPU to main memory.
• The address bus is one-way, so addresses are only sent from the CPU to main memory.
• The data bus carries instructions and data between the CPU and main memory, so it is bi-directional.
• The width of the data bus affects how many bits can be transferred at one time.
• The control bus carries control signals such as read and write signals, so main memory knows whether the CPU wants to read an instruction or write data.
• The control bus carries signals from the control unit to coordinate the components during the fetch-decode-execute cycle.

The role of the clock

• The clock sends regular pulses that synchronise the actions of the CPU and main memory.
• Each clock pulse triggers the next step of the fetch-decode-execute cycle, so the stages happen in the correct order.
• The clock provides a regular timing signal so that the fetch-decode-execute cycle repeats at a steady rate.
• The clock is separate from the control bus; the control bus carries control signals, while the clock provides timing pulses.
• Do not credit the address bus storing addresses, the data bus storing data, or the control bus controlling the computer without naming a control signal; do not credit clock speed affecting performance as a role in the cycle.
• Level 3 responses must cover all three bullets and link them to the fetch-decode-execute cycle; Level 2 answers may identify roles but link them only partly to the cycle.

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)

Indicative content

Why secondary storage is needed

• Secondary storage is non-volatile, so it keeps the operating system, applications and students' work when the power is turned off.
• It stores programs and files that are not currently in use, so they are not lost when the computer is switched off.
• It provides a larger capacity than primary storage for files such as students' work, videos and photographs.
• It allows each computer to keep many students' files and the software the school has installed.

The difference between primary and secondary storage

• Primary storage (RAM) is volatile and directly accessible by the CPU; secondary storage is non-volatile and not directly accessible by the CPU.
• RAM holds the data and instructions currently in use; secondary storage holds data and programs long term.
• Primary storage is faster but smaller and more expensive per gigabyte; secondary storage is slower but larger and cheaper.
• The school's computers need both: RAM to run the operating system and applications, and secondary storage to keep them when the computer is switched off.

A suitable type of secondary storage for the school's computers and a reason why it is suitable

• A solid state drive (SSD) is suitable because it has no moving parts, so it is durable and quiet, and has fast read/write speeds, which helps the computers start up quickly.
• A magnetic hard disk drive (HDD) is suitable because it is cheap and offers a very large capacity, which is useful for storing many students' files.
• Either type could be used; a small SSD for the operating system and applications plus a large HDD for files would balance speed and cost.

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

• Award credit for a type of secondary storage only when a reason is given that is linked to the school's computers; a named type alone (e.g. 'SSD') is not creditworthy. Do not accept RAM as secondary storage or the claim that secondary storage is the same as RAM. Do not accept CD/DVD/Blu-ray as the main storage for the school's computers because their capacity is too low and write speeds are slow.
• For Level 3, the answer must cover all three bullets and apply at least one point to the school's computers. A 6-mark answer is well developed with sustained reasoning and a justified choice; a 5-mark answer covers all three but with limited development or application. Comparisons of speed and cost between primary and secondary storage are creditworthy as part of the difference.