Compiled languages usually run faster because the entire source program is translated into machine code before execution, whereas interpreted code is translated or processed while the program is running. This gives compiled programs less translation overhead during execution.
A compiler translates the complete source code into executable machine code before the program runs. The processor can then execute these machine-code instructions directly whenever the program is launched.
An interpreter generally translates and executes source code one instruction or statement at a time. During execution, it must repeatedly analyze instructions, determine their meaning, and perform the required operations. This creates runtime overhead.
| Factor | Compiled language | Interpreted language |
|---|---|---|
| Translation time | Before execution | During execution |
| Executable output | Usually produces machine code or an executable file | Usually requires the interpreter each time |
| Optimization | Compiler can optimize the program as a whole | Optimization may be limited by runtime translation |
| Repeated execution | Previously translated code can be reused | Translation or interpretation may recur |
Compilers can also perform code optimization before execution. For example, they may remove unreachable instructions, simplify calculations, or select more efficient machine instructions. Because the compiler can examine the whole program, it may identify optimization opportunities that an interpreter processing one statement at a time cannot.
However, “compiled always means faster” is a common misconception. Performance depends on the language implementation, hardware, program, and optimization techniques. Some interpreted environments use just-in-time compilation, which translates frequently executed code into machine code during runtime and can substantially improve performance. Compiled programs may also have an initial compilation delay, although this occurs before execution.
For IB Computer Science A1.4 Translation, distinguish compilation time from execution time. In an exam response, explain the mechanism rather than merely stating that compiled languages are faster: identify prior translation into machine code, reduced runtime translation overhead, and compiler optimization, then acknowledge that just-in-time compilation makes the comparison less absolute.
