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Bytecode, also termed portable code or p-code, is a form of designed for efficient execution by a software interpreter. Unlike , bytecodes are compact numeric codes, constants, and references (normally numeric addresses) that encode the result of parsing and semantic analysis of things like type, scope, and nesting depths of program objects. They thus allow much better performance than interpreting source code directly.

The name bytecode stems from instruction sets that have one- followed by optional parameters. Intermediate representations such as bytecode may be output by programming language implementations to ease interpretation, or it may be used to reduce hardware and dependence by allowing the same code to run , on different devices. Bytecode may often be either directly executed on a (a i.e., interpreter), or it may be further compiled into for better performance.

Since bytecode instructions are processed by software, they may be arbitrarily complex, but are nonetheless often akin to traditional hardware instructions: virtual are the most common, but virtual have been built also. The Implementation of Lua 5.0 involves a register-based virtual machine. is register based Different parts may often be stored in separate files, similar to , but dynamically loaded during execution.


Execution
A bytecode program may be executed by parsing and directly executing the instructions, one at a time. This kind of bytecode interpreter is very portable. Some systems, called dynamic translators, or just-in-time (JIT) compilers, translate bytecode into as necessary at runtime. This makes the virtual machine hardware-specific, but doesn't lose the portability of the bytecode. For example, Java and code is typically stored in bytecoded format, which is typically then JIT compiled to translate the bytecode to machine code before execution. This introduces a delay before a program is run, when bytecode is compiled to native machine code, but improves execution speed considerably compared to interpreting source code directly, normally by several orders of magnitude.

Because of its performance advantage, today many language implementations execute a program in two phases, first compiling the source code into bytecode, and then passing the bytecode to the virtual machine. There are bytecode based virtual machines of this sort for Java, Python, ,Although opcodes are generated each time the program is launched, and are always interpreted and not just-in-time compiled , and Forth (however, Forth is seldom compiled via bytecodes in this way, and its virtual machine is more generic instead). The implementation of and Ruby 1.8 instead work by walking an abstract syntax tree representation derived from the source code.

More recently, the authors of V8 and Dart have challenged the notion that intermediate bytecode is needed for fast and efficient VM implementation. Both of these language implementations currently do direct JIT compiling from source code to machine code with no bytecode intermediary.


Examples
  • executes in the ActionScript Virtual Machine (AVM), which is part of Flash Player and AIR. ActionScript code is typically transformed into bytecode format by a . Examples of compilers include one built into Adobe Flash Professional and one built into Adobe Flash Builder and available in the Adobe Flex SDK.
  • objects
  • BANCStar, originally bytecode for an interface-building tool but used also as a language
  • Berkeley Packet Filter
  • Byte Code Engineering Library
  • C to Java virtual machine compilers
  • implementation of used to compile only to bytecode for many years; however, now it also supports compiling to native code with the help of
  • and Scieneer Common Lisp implementations of can compile either to native code or to bytecode, which is far more compact
  • Common Intermediate Language executed by Common Language Runtime, used by .NET Framework languages such as C#
  • Dalvik bytecode, designed for the Android platform, is executed by the Dalvik virtual machine
  • Dis bytecode, designed for the Inferno (operating system), is executed by the Dis virtual machine
  • for the Eiffel programming language
  • EM, the Amsterdam Compiler Kit virtual machine used as an intermediate compiling language and as a modern bytecode language
  • is a text editor with most of its functions implemented by , its built-in dialect of Lisp. These features are compiled into bytecode. This architecture allows users to customize the editor with a high level language, which after compiling into bytecode yields reasonable performance.
  • Embeddable Common Lisp implementation of can compile to bytecode or C code
  • Ericsson implementation of Erlang uses BEAM bytecodes
  • Icon The Implementation of the Icon Programming Language and Unicon The Implementation of Icon and Unicon a Compendium programming languages
  • used the to make its software applications more portable
  • , which is executed by the Java virtual machine
  • KEYB, the keyboard driver with its resource file KEYBOARD.SYS containing layout information and short sequences executed by an interpreter inside the resident driver.
  • , a modular bytecode compiler and virtual machine
  • LSL, a scripting language used in virtual worlds compiles in bytecode running on a virtual machine. Second Life has the original Mono version, Inworldz developed the Phlox version.
  • Lua language uses a register-based bytecode virtual machine
  • m-code of the languageFor the details refer to
  • of the programming language
  • language optionally compiles to a compact bytecode form
  • of implementation of the Pascal language
  • Parrot virtual machine
  • Pick BASIC also referred to as Data BASIC or MultiValue BASIC
  • The R environment for statistical computing offers a bytecode compiler through the compiler package, now standard with R version 2.13.0. It is possible to compile this version of R so that the base and recommended packages exploit this.For the details refer to
  • Scheme 48 implementation of Scheme using bytecode interpreter
  • Bytecodes of many implementations of the language
  • The Spin interpreter built into the Parallax Propeller
  • The database engine translates SQL statements into a bespoke byte-code format.
  • SWEET16
  • compiles to bytecode
  • and for Ruby

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