Edexcel GCSE Computer Science (1CP2) Exam Questions

• A Address bus (1)
• The only correct answer is A. The correct answer is address bus. Do not accept 'address' on its own.
• B is not correct because the control bus carries control signals in both directions between the CPU and other components
• C is not correct because the data bus carries data in both directions between the CPU and main memory
• D is not correct because the system bus is the collection of all three buses

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

• Reduces/makes the size of a file smaller (1)
• No data is lost/removed (during compression) (1)
• The original file/data can be recreated/restored exactly (1)

Allow 'the compressed file takes up less storage space' for the first mark.

The second and third bullets are two ways of making the same point: award a maximum of one mark for them, so a response that says no data is lost and that the original file can be restored, but does not say the file is smaller, scores one mark.

Do not accept descriptions of lossy compression, e.g. 'it removes data that is not needed to make the file smaller'.

Ignore reference to download/transmission times, bandwidth and streaming, as these are benefits of compression and not part of the definition.

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

• A compiler produces object code/machine code/an executable (file) (1) whereas an interpreter produces no object code/translated file (1)
• A compiler produces a machine code file (1) that can be run on its own/without the compiler/translator being present (1)
• An interpreter produces no object code/file (1) because it translates and executes each line instead of saving translated code (1)
• The compiler's output can be saved/stored (1) and run again later, while interpreted code has to be translated again each time it is run (1)

Allow binary for machine code.

Allow executable/an executable for object code.

Do not accept responses about translating the whole program, reporting errors or the speed of execution.

Do not accept 'the interpreter translates/executes one line at a time' on its own: this is how it translates, not what it produces. It earns the development only when linked to no object code/translated file being produced.

Do not accept the interpreter producing object code/an executable.

Indicative content

Machine independence

• A high-level language is machine independent, so the same source code can be run on different types of computer with few or no changes.
• The company can write the program once and sell it to users with different computers, without rewriting the code for each type of computer.
• Only one version of the program needs to be written and maintained, so development takes the company less time.

Processor specificity

• A low-level language is processor-specific, so a program written for one processor will not run on a different processor without being rewritten.
• Assembly language instructions depend on the instruction set of the particular processor, so the company would need a separate version of the program for each type of computer.
• Writing a separate low-level version for every type of computer would take the company much longer than writing one high-level program.
• Low-level code gives direct control of the hardware of one processor, so it is better suited to device drivers than to a program that must run on many different computers.

Translation

• High-level source code is translated for each type of computer by a compiler or an interpreter, so one version of the source code is enough for all the users.
• Assembly language is translated into machine code by an assembler, and the assembler produces machine code for one specific processor only.
• Machine code is already in a form that one particular processor can execute directly, but the same machine code will not run on a different processor.
• Each high-level statement translates into several machine code instructions, so the programmer does not need to know the instruction set of the processor.

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 high-level machine independence and low-level processor specificity, with the effect on the company's decision.
• Do not award low-level language, assembly language or machine code as portable, or 'high-level languages are written in English/like English' as a reason for machine independence.