Opcode

In

Overview

Specifications and format of the opcodes are laid out in the instruction set architecture (ISA) of the processor in question, which may be a general CPU or a more specialized processing unit.^[10] Opcodes for a given instruction set can be described through the use of an opcode table detailing all possible opcodes. 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.^[10] 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, variable-length structure.^[10][11] Instruction sets can be extended through the use of opcode prefixes which add a subset of new instructions made up of existing opcodes following reserved byte sequences.^{[citation needed]}

Operands

Depending on architecture, the operands may be

Assembly language, or just assembly, is a low-level programming language, which uses mnemonic instructions and operands to represent machine code.^[10] This enhances the readability while still giving precise control over the machine instructions. Most programming is currently done using high-level programming languages,^[12] which are typically easier for humans to understand and write.^[10] These languages need to be compiled (translated into assembly language) by a system-specific compiler, or run through other compiled programs.^[13]

Software instruction sets

Opcodes can also be found in so-called

• Gadget (machine instruction sequence)
• Illegal opcode
• Syllable (computing)
• Fused operation

References