Bytecode, also termed portable code or p-code, is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readablesource code, bytecodes are compact numeric codes, constants, and references (normally numeric addresses) that encode the result of compiler parsing and performing semantic analysis of things like type, scope, and nesting depths of program objects.
The name bytecode stems from instruction sets that have one-byte 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 operating system dependence by allowing the same code to run cross-platform, on different devices. Bytecode may often be either directly executed on a virtual machine (a p-code machine i.e., interpreter), or it may be further compiled into machine code 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 object file, but dynamically loaded during 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 machine code as necessary at runtime. This makes the virtual machine hardware-specific, but doesn't lose the portability of the bytecode. For example, Java and Smalltalk 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 around an order of magnitude (10x).
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, PHP,Although PHP opcodes are generated each time the program is launched, and are always interpreted and not just-in-time compiledTcl, AWK and Forth (however, Forth is seldom compiled via bytecodes in this way, and its virtual machine is more generic instead). The implementation of Perl 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.
ActionScript 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 compiler. Examples of compilers include one built into Adobe Flash Professional and one built into Adobe Flash Builder and available in the Adobe Flex SDK.
EM, the Amsterdam Compiler Kit virtual machine used as an intermediate compiling language and as a modern bytecode language
Emacs is a text editor with most of its functions implemented by Emacs Lisp, 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 Common Lisp can compile to bytecode or C code
Ericsson implementation of Erlang uses BEAM bytecodes
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 Smalltalk language