bytekod

Bytekod, or bytecode in English, is a form of intermediate code executed by a virtual machine or interpreter rather than directly by hardware. It is designed to be portable across different platforms and to enable safer, more easily optimized execution. Compilers translate high-level language sources into bytekod, which can later be translated into native machine code at runtime or interpreted.

Bytekod typically consists of a sequence of instructions and operands, sometimes with metadata. Many implementations use a stack-based design where operations push and pop values on a stack; others use a register-based approach. Bytekod specifications may include type information, access modifiers, and verification rules to ensure safety and correctness before execution.

A runtime loads bytekod, verifies it to prevent illegal memory access or operations, and then executes it. Execution can occur through interpretation, which processes instructions directly, or through just-in-time (JIT) compilation, which translates hot paths to native machine code for speed. The combination supports portability across hardware and operating systems while enabling performance optimizations at runtime.

Prominent ecosystems include Java bytekod, run on the Java Virtual Machine; the Common Intermediate Language (CIL) used by the .NET framework; Python bytekod compiled from source files; Lua bytekod; and Android’s Dex bytekod for apps. These systems illustrate how bytekod serves as a portable, language-agnostic target that can be produced by compilers from various languages and executed by specialized runtimes.

The bytekod model emerged with the rise of virtual machines in the 1990s, popularized by Java. It provides portability and security but adds overhead relative to native code. Modern runtimes often blend bytekod with ahead-of-time or JIT translation to balance flexibility and performance.