In programming language implementation, what is the main difference between a compiler and an interpreter?

Introduction / Context:
Programming languages are implemented using compilers, interpreters or a combination of both. Understanding the difference between these two approaches is essential for reasoning about performance, error detection and portability. Many exam questions test whether you can clearly distinguish how a compiler works compared to an interpreter.

Given Data / Assumptions:

We have a high level source program written in a language such as C, Java or Python.
The goal is to execute this program on a specific machine architecture.
Two general strategies are compilation and interpretation.
The question asks for the main conceptual difference between these strategies.

Concept / Approach:
A compiler reads the entire source program, performs analysis and optimization and produces an equivalent target program, typically machine code or bytecode, which can then be executed many times without needing the source. Errors are usually reported at compile time before the program runs. An interpreter, in contrast, reads the program, translates and executes it incrementally, often line by line or statement by statement, directly at run time, without generating a separate standalone machine code file.

Step-by-Step Solution:
Step 1: When using a compiler, the compilation step is separate from execution. The compiler generates an executable file or intermediate code. Step 2: Once the compiled program is produced, it can be distributed and run multiple times without invoking the compiler again. Step 3: When using an interpreter, the source program or an intermediate representation is fed directly into the interpreter each time it runs, and the interpreter repeatedly performs translation and execution as it goes. Step 4: Compiled programs often run faster because translation overhead is paid once, whereas interpreted programs provide flexibility and easier debugging at the cost of additional run time overhead. Step 5: This behaviour matches the description in the correct option, which contrasts whole program translation before execution with statement by statement translation during execution.

Verification / Alternative check:
Compiler design textbooks describe compilation as a series of phases that end with code generation and linking, while interpretation is described as repeatedly fetching, analyzing and executing source level or intermediate instructions. Platform type, language category or absolute error reporting are not used as defining criteria in formal definitions.

Why Other Options Are Wrong:
Scripting versus system languages is a loose classification, and many languages can be implemented both ways.
Mainframes and personal computers can run both compilers and interpreters; hardware type is not the distinguishing feature.
Compilers do detect many errors at compile time, and interpreters cannot guarantee to report every possible error before execution.

Common Pitfalls:
A common mistake is to think that a language is by definition compiled or interpreted. In reality, many languages, such as Java and Python, have both compiled and interpreted implementations or use hybrid approaches with bytecode. For exam answers, focus on the conceptual difference in when and how translation occurs.

Final Answer:
The main difference is that a compiler translates the entire source program into a target program before execution, while an interpreter translates and executes the program incrementally at run time.