Understand that there are three common types of program translator:

The idea

A translator converts source code written by a programmer into a form the processor can execute. The specification names three common types: compiler, interpreter and assembler. A compiler translates the whole program in one go, producing an executable file; errors are reported after the whole program is translated, and the executable can then run without the compiler. An interpreter translates and executes the source code one statement at a time, stopping at the first error it meets, which makes it useful for testing and debugging but means the source (or interpreter) is needed each time the program runs. An assembler translates assembly language, with its mnemonics, into machine code. Each translator suits different circumstances: compilers for distributing finished programs, interpreters for development and step-by-step checking, assemblers for low-level assembly programs.

What earns the marks

• A compiler translates the whole source program in one go and produces an executable file.
• A compiler reports errors only after translating the whole program, and the resulting executable runs without needing the compiler.
• An interpreter translates and executes the source code one statement at a time, stopping when it reaches an error.
• An interpreter is useful during development and testing because errors are found as each statement is executed.
• An assembler translates assembly language (mnemonics) into machine code.
• Each translator suits different circumstances: compilers for distributing finished programs, interpreters for development, assemblers for low-level assembly programs.

Common mistakes and how to put them right

• Naming only one or two translators.

  Put it right by naming all three — compiler, interpreter and assembler.

• Confusing an interpreter with a compiler.

  Put it right by stating that an interpreter translates and executes one statement at a time, while a compiler translates the whole program before it runs.

• Describing an assembler as translating high-level code.

  Put it right by stating that an assembler translates assembly language into machine code.

• Saying a compiler finds all errors before running.

  Put it right by explaining that a compiler reports errors after translating the whole program, not that it guarantees an error-free program.

Exam tips

• Name all three translators explicitly: compiler, interpreter and assembler.
• For each translator, state what it takes as input and what it produces as output.
• Give a circumstance where each translator is the better choice, for example an interpreter for testing during development.
• Use precise vocabulary such as source code, machine code, executable and mnemonics.