Edexcel GCSE Computer Science (1CP2) Exam Questions

Award one mark for:

• Several/multiple machine code instructions (1)

The answer must refer to instructions.

Do not accept machine code on its own.

Do not accept binary on its own.

Do not accept 'one or more machine code instructions' as it does not show that one statement becomes several instructions.

Do not accept assembly code/compiled code/low-level code on their own.

Do not accept 'a line of code'/'a statement' as this repeats the question.

Award one mark for any of the following:

• Object code (1)
• Machine code (1)
• Executable code / an executable (1)

Allow object file.

Do not accept source code.

Do not accept high-level code.

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

• The interpreter executes each line as soon as it has been translated (1) so translation and execution happen together/at the same time (1)
• The compiler translates the whole program first (1) and the machine code is run later/separately (1)
• The interpreter translates the code and runs it while the program is running (1) whereas the compiler does not run the code it produces (1)
• The compiler produces translated code that is executed only after all the translation has finished (1) but the interpreter executes each line immediately (1)

Allow 'translates one line at a time' where it is linked to executing each line immediately.

Do not accept answers that only state that a compiler is faster/an interpreter is slower, without reference to when execution happens.

Do not accept answers that only give object code, error reporting or portability, without reference to when execution happens.

Do not accept the compiler executing the program as it translates it.

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

• The same source code can be used on different processors (1) because a compiler/interpreter for each processor translates it into that processor's machine code/instructions (1)
• The program is machine/processor independent (1) because the code is translated into the machine code/instructions of each processor it is run on (1)
• A different compiler/interpreter is used for each type of processor (1) so the same source code can be translated into each processor's machine code/instructions (1)
• The program can be moved/copied to a computer with a different processor (1) because a compiler/interpreter that produces code for that processor exists (1)

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

Do not accept 'it is portable' without a linked reason about translation for different processors.

Do not accept 'it is easier to use/read/write' on its own without a linked reason about translation/processors.

Do not accept 'it is not written in binary'/'it is not machine code'/'it is not written in assembly language' as the reason without saying that the code is translated into each processor's machine code/instructions.

Do not accept the misconception that the program runs directly on any processor without being translated.

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

• The programmer can control/manipulate the hardware directly (1) because low-level instructions can access registers/memory addresses/hardware features (1)
• The code can be made to work efficiently with a specific device (1) because low-level languages are processor/chipset specific, so the instructions match that hardware (1)
• The code produced is fast to execute (1) because it is optimised for the specific processor/uses few instructions (1)
• The code produced is small (1) so it fits in the limited memory/ROM available in the device (1)

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

Fast execution and small code size are typical advantages of low-level languages; award them only where the linked reason relates to the device.

Do not accept 'it is easier to write/learn/understand' or 'it is faster to write' as a point or as the expansion, because low-level languages are not easier for these.

Do not accept 'it is close to the hardware' or 'it works with hardware' without expansion of what that allows the program to do.

Do not accept 'because it is low-level' as the expansion; the answer must say what the language/hardware allows.

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

• The compiler produces object code/machine code for the whole program (1) so there is no complete executable until every line has been translated (1)
• The compiler translates all the source code before producing the object code (1) so the program cannot start until translation has finished (1)
• The compiler checks the whole program for errors during translation (1) so all of the source code must be read before an executable can be produced (1)

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

Allow 'in one go'/'all at once' for the translation point, but this does not earn the second mark unless it is linked to why the program cannot be executed until translation has finished.

A statement that the whole program is translated, with no linked reason about when the program can be executed, earns 1 mark only.

Do not accept 'a compiler is faster' or 'compiled code runs faster' on its own; this does not explain why translation must finish before execution.

Do not accept 'it translates and runs the program one line at a time', as this describes an interpreter.

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

• No object code/machine code file is stored/saved (1) so there is no translated program to run on the next occasion (1)
• The translation is only temporary/is lost when the program ends (1) because each line is translated as the program runs (1)
• No executable file is created/saved (1) so the whole program has to be translated again every time it is run (1)
• The interpreter translates each line while the program is running (1) so nothing is kept that could be run without the interpreter (1)

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

Do not accept 'it is interpreted' or 'it is not compiled' without saying that no object code/executable is stored/saved.

Do not accept 'the source code is high-level so it must be translated' or 'the source code has to be turned into machine code' on its own, as this is true of any translation.

Do not accept answers about the source code being deleted.

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

• The compiler translates the whole program into machine code before it is run (1) so no translation is needed while the program is executing (1)
• The machine code/object code is already produced before execution (1) so the CPU can carry out the instructions directly without translating them (1)
• The compiled program does not need an interpreter at run time (1) so no time is spent translating each line before it is executed (1)

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

A statement that translation happens before execution, with no linked reason for faster running, earns 1 mark only.

Do not accept 'faster to run' or 'quicker' on its own without a reason linked to translation before/during execution.

Do not accept 'compiled code is optimised' or 'compilation takes less time' without linking this to translation before execution/at run time.

Do not accept answers about the compiler being installed or available.

The question asks why a compiled program usually runs faster, so answers must refer to when translation happens, not just general performance claims.

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.

Indicative content

How each translator deals with a syntax error

• An interpreter stops as soon as it finds a syntax error and displays an error message.
• With an interpreter, the lines before the error have already been executed, so the student can see how far the program got before it stopped.
• A compiler reports errors at the end of translation, so the student gets a list of all the syntax errors in the program in one go.

How much of the program is translated at a time

• An interpreter translates one line at a time and executes each line immediately.
• A compiler translates the whole program in one go before any of it is run.
• A compiler produces object code, so after every change the whole program must be compiled again before the student can run it.
• An interpreter produces no object code, so the student does not have to wait for the whole program to be translated before it runs.

How this affects the student's testing

• An interpreter suits this student because the program can be run straight away after each small change.
• The interpreter stops at the first error found, so the student fixes that error and runs the program again, but may only find the next error on the next run.
• Reporting every error at the end of compilation means the student can fix several errors at once, but cannot run the program until the whole program compiles.
• The student should use an interpreter while testing, and compile the finished program once it works.

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 relate the way each translator works to the student's testing, not just describe the two translators.

Do not accept answers about run-time or logic errors where no comparison of the translators is made.