[[International Standard Name Identifier|In]] [[computing]], an '''opcode'''<ref name="Barron_1978_Opcode"/><ref name="Chiba_2007"/> (abbreviated from '''operation code''',<ref name="Barron_1978_Opcode"/> also known as '''instruction machine code''',<ref name="Intel_1973_MCS-4"/> '''instruction code''',<ref name="Intel_1974_MCS-40"/> '''instruction syllable''',<ref name="Jones_1988_CISC"/><ref name="Domagała_2012"/><ref name="Smotherman_2013"/><ref name="Jones_2016_CISC"/> '''instruction parcel''' or '''opstring'''<ref name="Schulman_2005"/><ref name="Chiba_2007"/>) is the portion of a [[machine code|machine language]] [[instruction (computer science)|instruction]] that specifies the operation to be performed. Beside the opcode itself, most instructions also specify the data they will process, in the form of [[operand]]s. In addition to opcodes used in the [[instruction set architecture]]s of various [[CPU]]s, which are hardware devices, they can also be used in [[virtual machine#Process virtual machines|abstract computing machines]] as part of their [[byte code]] specifications.
