In computer science, an opcode (operation code) is the portion of a machine language instruction that specifies the operation to be performed. Their specification and format are laid out in the instruction set architecture of the processor in question (which may be a general CPU or a more specialized processing unit). Apart from the opcode itself, an instruction normally also has one or more specifiers for operands (i.e. data) on which the operation should act, although some operations may have implicit operands, or none at all. There are instruction sets with nearly uniform fields for opcode and operand specifiers, as well as others (the x86 architecture for instance) with a more complicated, varied length structure. [1]

Depending on architecture, the operands may be register values, values in the stack, other memory values, I/O ports, etc., specified and accessed using more or less complex addressing modes. The types of operations include arithmetics, data copying, logical operations, and program control, as well as special instructions (such as CPUID and others).



Assembly language, or just assembly, is a low-level programming language, which uses mnemonics, instructions and operands to represent machine code. This enhances the readability while still giving precise control over the machine instructions. Most programming is currently done using high-level programming languages,[2][3] which are typically easier to read and write. These languages need to be compiled (translated into machine language), or run through other compiled programs.[4]

Software instruction sets

Opcodes can also be found in so called byte codes and other representations intended for a software interpreter rather than a hardware device. These software based instruction sets often employ slightly higher-level data types and operations than most hardware counterparts, but are nevertheless constructed along similar lines. Examples include the Java programming language's Java Virtual Machine (JVM), the byte code used in GNU Emacs for compiled LISP code, .NET Common Intermediate Language (CIL), and many others.[5]

See also


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  • Opcode —   [Abk. für Operation Code], Teil einer Anweisung in Maschinensprache. Ähnlich wie bei höheren Programmiersprachen bestehen Programmbefehle in Maschinensprache aus einem Anweisungsteil, dem Opcode, und einem Datenteil. Der Opcode legt den… …   Universal-Lexikon

  • opcode — /opˈkōd/ noun A code containing operation instructions for a microprocessor ORIGIN: operation, and ↑code …   Useful english dictionary

  • Opcode — Ein Opcode, auch op code oder operation code, ist eine Zahl, die die Nummer eines Maschinenbefehls für einen bestimmten Prozessortyp angibt. Alle Opcodes zusammen bilden den Befehlssatz des Prozessors oder der Prozessorfamilie. Jeder Befehl hat… …   Deutsch Wikipedia

  • Opcode — Langage machine Le langage machine, ou code machine, est la suite de bits qui est interprétée par le processeur d un ordinateur exécutant un programme informatique. C est le langage natif d un processeur, c est à dire le seul qu il puisse traiter …   Wikipédia en Français

  • opcode — noun A mnemonic used to refer to a microprocessor instruction in assembly language …   Wiktionary

  • Opcode — Operation(al) Code …   Acronyms

  • opcode — ● ►en n. m. ►PROG Code d opération. En général, c est le numéro qui identifie une fonction dans une bibliothèque, ou une instruction parmi celles qui constituent le jeu d instructions d un processeur …   Dictionnaire d'informatique francophone

  • Opcode — Operation(al) Code …   Acronyms von A bis Z

  • opcode — abbr. Operation Code …   Dictionary of English abbreviation

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