Knowledge Organiser: Translators (Compiler, Interpreter, Assembler)
Key Terms
- Compiler: Translates the entire high-level program into machine code all at once, producing an executable file
- Interpreter: Translates and executes a high-level program one line at a time — no output file created
- Assembler: Translates Assembly language mnemonics into machine code (near one-to-one translation)
- Source code: The original high-level or assembly program written by the programmer
- Executable file: The compiled machine code file that can run directly without translation
Must-Know Facts
- Compiler: translates ALL at once → creates executable → fast execution → reports all errors after compilation
- Interpreter: translates ONE LINE at a time → no file created → slower execution → stops at first error
- Assembler: translates Assembly mnemonics → machine code (1-to-1 mapping)
- Compiled programs can be shared without source code; interpreted programs need source code every time
- Interpreter is easier for development/testing (instant feedback); compiler is faster for final distribution
- All three translators convert code the CPU cannot understand into machine code it can
Key Concepts
- Compiler = translate whole book first, then read quickly; Interpreter = translate each sentence as you go
- Interpreter advantage: easier debugging (stops at first error with line number shown)
- Compiler advantage: faster execution; distributable without source code
- Assembler is processor-specific — Assembly code for one CPU type won't assemble for another
Common Mistakes
- Confusing compiler and interpreter behaviour on errors: A compiler reports ALL errors after translating the whole program; an interpreter stops at the FIRST error it encounters — different error reporting behaviour
- Saying compiled programs run slower: Compiled programs run FASTER because translation has already been done — the executable runs directly on the CPU without re-translating each time
- Forgetting the assembler as a third type: Many students only mention compiler and interpreter — the assembler (which translates Assembly mnemonics to machine code) is a distinct third translator type
- Confusing Assembly language with machine code: Assembly uses human-readable mnemonics (LDA, ADD, STA); machine code is pure binary (0s and 1s) — they are different levels of language
- Saying interpreted programs cannot be distributed: Interpreted programs can be distributed — but the recipient needs both the source code and an interpreter installed, unlike compiled executables which run standalone