In IB Computer Science HL, students are expected to understand how high-level code is translated into machine code. This means clearly distinguishing between interpreters, compilers, and Just-In-Time (JIT) compilation.
Many students confuse these terms or treat them as interchangeable. In IB exams, this leads to vague answers and lost marks. Each approach works differently and has distinct advantages and disadvantages.
Why Code Translation Is Needed
Computers do not understand high-level programming languages. All programs must eventually be converted into machine code before they can run.
The method used to perform this translation affects:
- Execution speed
- Error detection
- Portability
- Memory usage
This is why interpreters, compilers, and JIT systems exist.
What Is an Interpreter?
An interpreter translates and executes code line by line, one statement at a time.
How it works:
- Reads one line of source code
- Translates it into machine code
- Executes it immediately
- Moves to the next line
Key characteristics:
- No separate executable file
- Errors are reported one at a time
- Execution is slower than compiled code
Advantages:
- Easy debugging
- Platform independence (with the right interpreter)
- Faster development cycle
Disadvantages:
- Slower execution
- Program must be interpreted every time it runs
In IB terms, interpreters prioritise flexibility over performance.
What Is a Compiler?
A compiler translates the entire program into machine code before execution.
How it works:
- Reads all source code
- Translates it into machine code
- Produces an executable file
- The executable runs independently
Key characteristics:
- Errors are detected all at once
- Faster execution once compiled
- Platform-specific executables
Advantages:
- High execution speed
- Optimised machine code
- No need for source code during execution
Disadvantages:
- Slower development cycle
- Less flexible across platforms
In IB exams, compilers are associated with performance and efficiency.
What Is Just-In-Time (JIT) Compilation?
JIT compilation combines features of both interpretation and compilation.
How it works:
- Code is initially interpreted
- Frequently used sections are compiled at runtime
- Compiled sections are reused
This approach:
- Improves performance over pure interpretation
- Retains flexibility
- Optimises code dynamically
JIT is commonly used in:
- Virtual machines
- Managed runtime environments
IB HL students should understand JIT as a hybrid approach.
Comparing Interpreters, Compilers, and JIT
For IB Computer Science HL, students should compare based on:
- Interpreter: flexible, slower, line-by-line
- Compiler: fast execution, less flexible, pre-compiled
- JIT: balance of speed and flexibility
Clear comparison is more important than memorising examples.
Common Student Mistakes
Students often:
- Say interpreters are “simpler compilers”
- Forget when translation happens
- Ignore performance trade-offs
- Confuse JIT with full compilation
Accuracy matters.
Final Thoughts
Interpreters, compilers, and JIT compilation represent different strategies for executing programs. Each exists because software development balances speed, flexibility, and efficiency differently depending on context.
Understanding these differences allows IB Computer Science HL students to explain how programs actually run — a key skill assessed in higher-level questions.
