Programming languages: high-level vs low-level

OCR J277 Paper 2 tests language levels and translators — usually 4–6 mark questions. Know the characteristics, advantages and disadvantages of each level, and which translator is used for each.

Levels of programming language

Machine code (level 0 — lowest level)

• Binary instructions that the CPU executes directly (no translation needed).
• Specific to a particular CPU architecture (not portable).
• Very difficult for humans to read and write.
• Used in: no modern development — only generated by compilers/assemblers.

Assembly language (low-level)

• Uses mnemonics (short abbreviations) to represent machine code instructions.
• One-to-one correspondence with machine code: one assembly instruction = one machine code instruction.
• Translated by an assembler.
• Advantages: direct hardware control; very efficient; used for device drivers, embedded systems, real-time systems.
• Disadvantages: complex; not portable (tied to CPU architecture); hard to debug.

High-level languages (e.g. Python, Java, C++, C#)

• Written in a human-readable form with English-like syntax.
• One statement can generate many machine code instructions.
• Translated by a compiler or interpreter.
• Advantages: easier to write, read and debug; portable (can run on different hardware); faster development.
• Disadvantages: slightly less efficient than hand-written assembly; less direct hardware control.

Translators

Translator	How it works	Advantage	Disadvantage
Assembler	Converts assembly language into machine code	Direct one-to-one translation	Only for assembly language
Compiler	Translates the entire source code into machine code at once; produces an executable	Fast at run time (no translation needed during execution); source code protected (not distributed)	Slow compilation; errors all reported together; not interactive
Interpreter	Translates and executes one line at a time	Easy to debug (stops at first error); cross-platform	Slower at run time (translating each time it runs); source code must be distributed

When to use each translator

• Compiler: production software where speed matters; distributing software without sharing source code (e.g. commercial apps).
• Interpreter: development/testing (easier debugging); scripting languages; Python in interactive mode; web browsers executing JavaScript (JIT compilation is a mix).

Common OCR exam mistakes

1. Saying machine code "needs to be translated" — it does NOT. It runs directly on the CPU.
2. Saying compilers are "better" than interpreters — it depends on the use case. Interpreters are better for debugging; compilers are better for production performance.
3. Confusing assembler with compiler — an assembler converts assembly language (mnemonics); a compiler converts high-level language code.
4. Forgetting portability: high-level languages are generally portable (can run on different hardware if a compatible interpreter/compiler exists); machine code and assembly are not portable.