Definition

Compilers can be classified by number of passes over the source, and by the relationship between source/target platforms.

Key Points

• By number of passes
  • Single-pass compiler: scans source once (e.g., Pascal) — fast, limited optimization
  • Multi-pass compiler: multiple scans, each pass builds on the previous (e.g., most modern compilers) — better optimization, more memory/time
• By platform relationship
  • Native compiler: generates code for the same machine it runs on
  • Cross compiler: runs on one machine, generates code for another (common in embedded systems)
  • Source-to-source (transpiler): converts one high-level language to another (e.g., TypeScript → JavaScript)
• By execution model
  • Bootstrap compiler: written in the language it compiles, used to build itself
  • Just-In-Time (JIT) compiler: compiles at runtime, blending compilation and interpretation (e.g., JVM, V8)

Example

• Cross compiler: compiling ARM firmware code on an x86 desktop
• JIT: Java HotSpot compiling hot bytecode paths to native code during execution

📌 CSS Frequency: Low-moderate — usually a short definitional sub-part of a broader compiler-types question.

Model Answer (short)

"Compilers are classified by passes (single-pass vs multi-pass) and by platform (native vs cross-compiler vs source-to-source translator). A cross compiler is especially important in embedded systems, where code is compiled on a powerful host machine but targets a resource-constrained device."