Primary Memory 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

• B RAM is faster to access than secondary storage (1)
• The only correct answer is B. The correct answer is RAM is faster to access than secondary storage.
• A is not correct because RAM is volatile
• C is not correct because RAM has a smaller capacity than secondary storage
• D is not correct because RAM is more expensive than secondary storage

• A The next instruction (1)
• The only correct answer is A. The correct answer is the next instruction.
• B is not correct because data is fetched during the execute stage
• C is not correct because an instruction is decoded after it is fetched
• D is not correct because the program counter holds the address used to fetch the instruction

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:

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

• The program instructions and data are stored together in main memory/RAM (1)
• The same memory is used for both instructions and data (1)
• The instructions are fetched from main memory and executed by the CPU (1)
• The instructions are fetched and executed one at a time / in sequence (1)
• The program can be changed/replaced by loading new instructions into memory, without changing the hardware (1)

Do not accept the program is stored in secondary storage / on the hard disk.

Do not accept the program is stored in the CPU / in registers.

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

• Holds/stores the data and instructions of the program currently being run (1) to be fetched by the CPU during the fetch-decode-execute cycle (1)
• Instructions and data are loaded/copied from secondary storage into RAM (1) before they can be processed by the CPU (1)
• Stores the program that is currently running (1) together with the data that it uses (1)
• Holds the data and instructions that the CPU needs next (1) so the CPU can access them quickly (1)

Allow a response that describes both that RAM holds the current program and that the program was loaded from secondary storage into RAM, provided each statement is linked to a development.

Do not accept responses about cache or registers as the store of the current program.

Do not accept responses that say RAM stores data permanently or that RAM is read-only.

Do not accept 'RAM is where the CPU processes data' (this describes the ALU/registers), or 'RAM stores the operating system' unless it is linked to the program currently being run.

Do not award a second mark for a response that only states that RAM holds data and instructions with no linked development.

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 description such as:

• RAM can be read from/written to much faster than secondary storage (1) so the CPU can fetch the instructions and data quickly enough to keep working/does not idle (1)
• The CPU can fetch/execute instructions faster than they can be read from secondary storage (1) so instructions and data are copied into RAM to avoid the CPU waiting/idling (1)
• RAM is connected to the CPU by the address/data/control buses (1) so the CPU can fetch instructions and data directly from main memory during the fetch-decode-execute cycle (1)

For each linked description, the first mark is for the point and the second mark is for a valid development linked to it. A point with no development scores 0. A development that only repeats the point (for example, 'so data can be accessed faster') does not earn the second mark, but the point can still earn one mark.

Do not accept responses that only restate the question, such as 'so the program is copied into RAM'.

Do not accept responses about RAM being volatile, being permanent/non-volatile storage or having a large capacity.

Do not award for a response that only says the CPU cannot run instructions directly from secondary storage, or that the CPU can only directly access main memory, unless it is linked to why this means RAM gives faster access (for example, so the CPU does not wait).

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

• RAM is volatile (memory) (1) because it needs a constant/continuous power supply to hold/store the data it contains (1)
• Data is held in RAM as electrical states/charges (1) so when the power supply is removed these states cannot be kept/refreshed and the data is lost (1)
• RAM is used as short-term storage for the data and instructions currently in use (1) because it can only hold them while the computer has power (1)

For both marks, the expansion must follow/associate with the statement and must link the loss of the data to the power supply being removed.

Accept 'RAM is volatile' on its own for the first mark; the second mark is only awarded for a linked reason about the power supply.

Do not accept 'RAM is temporary/short-term memory' or 'RAM is cleared when the computer is switched off' on its own for both marks, as neither gives a reason.

Do not accept answers that say the data is deleted/cleared/erased by the computer or the operating system, or that the data is saved/moved to secondary storage, without saying why the data cannot be kept (e.g. because RAM needs power/is volatile).

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

• More applications/programs can be open/run at the same time (1) because more instructions and data can be held in main memory at once (1)
• Programs run faster (1) because the CPU does not have to wait for instructions/data to be read/transferred from slower secondary storage (1)
• The CPU waits/idles for less time (1) because instructions and data can be transferred to the CPU more quickly from RAM (1)

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

Do not accept 'more files/photos/documents can be stored' or 'the computer has more storage' - this is a benefit of secondary storage, not RAM.

Do not accept 'the CPU becomes faster' or 'the clock speed increases'.

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.

Indicative content

the role of RAM in the stored program concept

• In the von Neumann stored program concept, a program's instructions and the data it uses are held together in main memory.
• RAM holds the instructions and data of the program that the CPU is currently processing.
• The CPU fetches each instruction from RAM during the fetch-decode-execute cycle, so a program must be in RAM before it can be run.
• RAM is directly accessible by the CPU, so instructions can be fetched quickly enough for the CPU to keep working.

what happens to a program when it is opened

• When a program is opened, a copy of its instructions and data is transferred from secondary storage, such as the hard drive, into RAM.
• The operating system loads the program into RAM so that the CPU can start fetching and executing its instructions.
• When the program is closed, it is removed from RAM, and the space it used is free for another program.
• If a computer does not have enough RAM, the program may not open, or another open program has to be closed first.

why the CPU cannot execute a program directly from secondary storage

• Secondary storage, such as a hard disk drive, is much slower to access than RAM.
• The CPU can process instructions much faster than secondary storage can supply them, so the CPU would have to wait and would not be working at full speed.
• RAM is fast electronic memory with no moving parts, so data can be read from it in a fraction of the time taken by a magnetic hard disk drive.
• Running the school's programs directly from secondary storage would make the computers in the IT room very slow to use.

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 responses must cover both the role of RAM in the stored program concept and the speed difference between RAM and secondary storage, with a reason such as the CPU having to wait for instructions.
• Answers that make only basic, independent points, such as what RAM is, that a program is copied into RAM when it is opened, or that RAM is faster than a hard drive, without linking them to explain why the CPU would have to wait for instructions, are limited to Level 1.
• Do not accept statements that RAM is permanent storage, that RAM replaces secondary storage, or that secondary storage is read-only.

Indicative content

Why the report was lost

• The report was being created and edited in RAM, which is volatile.
• Volatile memory loses its contents when the power supply is removed.
• The power cut removed the power, so the data in RAM was lost.
• The report had not been saved to secondary storage before the power cut.
• Only data that had been saved to secondary storage would remain after the power cut.

The difference between RAM and secondary storage

• RAM is volatile and holds data temporarily while the computer is on.
• Secondary storage is non-volatile and keeps data permanently when the power is off.
• RAM is directly accessible by the CPU and is much faster than secondary storage.
• Secondary storage has a larger capacity and is cheaper per gigabyte than RAM.
• RAM holds the programs and data currently in use; secondary storage holds files for long-term storage.

How the employee could prevent this in future

• The employee should save the report regularly to secondary storage, such as the hard drive or a USB flash drive.
• The employee could enable autosave or autosave/recovery features in the word processor.
• The employee could use cloud storage that saves changes automatically.
• The employee could use an uninterruptible power supply (UPS) or battery to keep the laptop on during a power cut.
• The employee should not rely on RAM to keep work permanently.

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 responses must explain that RAM is volatile and contrast this with non-volatile secondary storage.
• Do not award marks for stating that the report was lost from secondary storage unless it had been saved there.

Indicative content

How RAM is used when editing video

• The editing software and the video project being worked on are loaded into RAM so that the CPU can access them quickly.
• RAM holds the frames, effects and timeline data that the CPU is processing as part of the fetch-decode-execute cycle.
• The CPU fetches the instructions and the video data it needs from RAM, which is much faster than fetching them from secondary storage.
• Having more RAM means that more of the 4K video project and its effects can be held in memory at the same time.
• RAM is also used by the operating system and any other open software, so not all of the RAM is available to the editing software.

Why too little RAM causes poor performance

• If there is not enough RAM, the operating system uses virtual memory on secondary storage for data that will not fit in RAM.
• Virtual memory is much slower than RAM, so the editor waits longer for 4K video to load and for effects to be applied.
• Data has to be swapped between RAM and virtual memory, which is extra work that slows the computer down.
• The editing software may freeze or close if it runs out of memory while working on the 4K video.
• Playback of the 4K video is not smooth because the frames cannot all be held in RAM ready for the CPU.

Why adding more RAM may not always improve performance

• If the computer already has enough RAM for the editing software, the extra RAM will not be used and performance will hardly change.
• The clock speed and the number of cores of the CPU decide how quickly instructions are processed, so a slow CPU will still limit how quickly the video is edited.
• A slow secondary storage drive will still limit how quickly the 4K video files can be loaded into RAM.
• Adding RAM only improves performance if a shortage of RAM was the reason for the computer being slow.

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 responses must explain how RAM is used when editing video and give a developed reason why adding more RAM may not always improve performance; responses that only explain how RAM is used, or only why too little RAM causes poor performance, are limited to Level 2.
• Accept 'paging' or 'swap file' as equivalent to virtual memory, but do not accept 'cache' or 'ROM'; do not credit statements that adding RAM increases the CPU clock speed or makes the CPU faster, or that 'RAM is volatile' explains poor performance, as these are not linked to the question asked.