opkoder

Opkoder (singular: opkode) is the set of codes that specify the operation to be performed by a computer's processor in a machine language instruction. In most instruction set architectures, a processor instruction is composed of an opcode field plus one or more operands and sometimes addressing-mode information. The opcode determines the basic operation (for example, add, load, store, jump) that the processor should perform; operands indicate the data or addresses to use, and addressing modes define how to interpret those operands.

Encoding and structure: The size and layout of opcodes vary by architecture. Some use fixed-width instructions with a dedicated opcode field; others use variable-length encodings or multibyte prefixes to extend the opcode space. In many systems, opcodes are represented by binary patterns that are mapped to semantic operations in the processor's control logic or microcode.

Role and usage: Opkoder are central to machine language, assembly language, and the design of software tools such as assemblers, disassemblers, emulators, and linters? emulators, and compilers. Understanding opcodes is essential for low-level programming, performance analysis, and reverse engineering. Modern CPUs often use complex instruction sets with numerous opcodes, while RISC architectures emphasize a smaller, more regular opcode set with broader use of addressing modes.

History and terminology: The term opkoder derives from op-code, and in Danish-language literature is the standard term for the operation code field of an instruction. The concept predates modern microarchitectures and appears in early computers as well as contemporary ISAs.