opkoodi

Opkoodi, or opcode, is the portion of a machine language instruction that specifies the operation the processor should perform. It is used by the instruction decoder to select the appropriate arithmetic, logic, control, or memory operation, which is then carried out in conjunction with operands such as registers or memory addresses.

The opcode forms a core part of an instruction set architecture (ISA). Depending on the architecture, opcodes may be fixed in size or variable in length, and they may be augmented by prefixes, secondary codes, or additional fields to extend the set of operations. Some CPUs use a dense opcode space with many distinct codes, while others rely on a smaller primary set supplemented by modifiers. In modern processors, decoding the opcode is often the first step in a pipeline that may translate the instruction into micro-operations or microcode, enabling flexible and efficient execution.

In human-readable form, opcodes are represented by mnemonics in assembly language, such as ADD, MOV, LOAD, or STORE. An assembler translates these mnemonics into the corresponding binary opcodes and operand encoding. A disassembler performs the reverse, converting binary instructions back into mnemonics for analysis or debugging. The exact meaning and encoding of opcodes are architecture-specific, varying across different CPUs and generations.

Opkoodi design influences instruction density, decoding speed, and energy use. Differences between architectures—such as fixed-width RISC designs versus variable-length CISC designs—lead to different trade-offs in how operations are represented and executed.