Architecture
Opcode
The portion of an instruction that specifies the operation to be performed.
Detailed Explanation
The opcode (operation code) tells the processor what to do—ADD, LOAD, BRANCH, etc. Instruction decoders examine the opcode to activate appropriate execution units and control signals.
Opcode encoding affects decoder complexity and instruction density. RISC architectures use fixed opcode positions for simpler decoding. Variable-length instructions may have opcodes of different sizes.