Bytecode is computer object code that is processed by a program, usually referred to as a virtual machine, rather than by the "real" computer machine, the hardware processor. The virtual machine converts each generalized machine instruction into a specific machine instruction or instructions that this computer's processor will understand. Bytecode is the result of compiling source code written in a language that supports this approach. Most computer languages, such as C and C++, require a separate compiler for each computer platform - that is, for each computer operating system and the hardware set of instructions that it is built on. Windows and the Intel line of microprocessor architectures are one platform; Apple and the PowerPC processors are another. Using a language that comes with a virtual machine for each platform, your source language statements need to be compiled only once and will then run on any platform.
The best-known language today that uses the bytecode and virtual machine approach is Java. The LISP language, used in artificial intelligence applications, is an earlier language that compiled bytecode. Other languages that use bytecode or a similar approach include Icon and Prolog.
Rather than being interpreted one instruction at a time, Java bytecode can be recompiled at each particular system platform by a just-in-time compiler. Usually, this will enable the Java program to run faster. In Java, bytecode is contained in a binary file with a .CLASS suffix.