Bytecode facts for kids

Bytecode is a special kind of computer code that helps programs run smoothly. Think of it as a secret language that computers understand better than regular human-written code. It's like a middle step between the code a programmer writes and the code a computer's processor can directly use.

Unlike the code you might see a programmer write (called source code), bytecode is made of small, coded instructions and numbers. These instructions are created after a special program, called a compiler, has checked the original code. Bytecode is very compact, meaning it takes up less space.

The name "bytecode" comes from the fact that its instructions often use one-byte codes, followed by other information. This type of code is super useful because it helps programs work on many different kinds of computers and devices without needing to be completely rewritten for each one. This is called being cross-platform.

Bytecode can either be run directly by a special program called a virtual machine (VM), or it can be changed even further into machine code. Machine code is the computer's native language, which helps the program run even faster.

How Does Bytecode Work?

A bytecode program can be run by reading and performing its instructions one by one. This is done by a bytecode interpreter, which is a program that understands and executes bytecode. This method is very flexible and allows the program to run on many different systems.

Some systems use something called a Just-In-Time (JIT) compiler. This special program translates the bytecode into machine code (the computer's direct language) right when the program is about to run. This makes the program run much faster, sometimes ten times faster, than just interpreting the bytecode directly. Even though the JIT compiler makes the program specific to the computer it's running on, the original bytecode is still portable.

For example, programs written in Java and Smalltalk are often saved as bytecode. When you run them, a JIT compiler quickly changes that bytecode into machine code. This makes the program start a little slower because of the translation, but it runs much faster afterward.

Because of this speed advantage, many programming languages today first turn their source code into bytecode. Then, a virtual machine runs this bytecode. Languages like Java, Python, and PHP use this method.

Examples of Bytecode

Many programming languages and systems use bytecode to make their programs work efficiently and on different devices. Here are some examples:

• ActionScript: This language, used for Flash Player and AIR, turns its code into bytecode for the ActionScript Virtual Machine (AVM).
• Android: The Android platform uses a special kind of bytecode called Dalvik bytecode, which runs on the Dalvik virtual machine.
• C#: Languages like C# (used in .NET Framework) compile into Common Intermediate Language (CIL) bytecode, which is run by the Common Language Runtime.
• Emacs: This popular text editor uses Emacs Lisp, its own programming language. Many of its features are compiled into bytecode, allowing users to customize it with good performance.
• Erlang: The Ericsson version of Erlang uses BEAM bytecodes.
• Java: Java bytecode is very famous and is run by the Java Virtual Machine (JVM). This is why Java programs can run on almost any device.
• Lua: This language uses a register-based bytecode virtual machine.
• MATLAB: The m-code of the MATLAB language is a form of bytecode.
• OCaml: This language can optionally compile its code into a compact bytecode form.
• Pascal: The UCSD Pascal system used p-code, which was an early form of bytecode.
• Python: When you run a Python program, it's often compiled into bytecode first. You can even see this bytecode using a special tool called `dis`.
• R: This language, used for statistics, has a bytecode compiler that can make programs run faster.
• Ruby: Languages like Ruby (especially YARV and Rubinius) use bytecode.
• Smalltalk: Many versions of the Smalltalk language use bytecodes.
• SQLite: This database system translates SQL commands into its own special bytecode format.
• WebAssembly: This is a new type of bytecode designed to run very fast in web browsers, allowing complex applications to run directly on the web.

See also

In Spanish: Bytecode para niños