Interactive explainer: CPU instruction operands, source vs destination, DEC example, and state transition model
Anatomy of an instruction
DEC
opcode
what to do
RAX
destination operand
encoded as register index
DEC has one operand — the destination.
The CPU reads from it, subtracts 1, writes back.
The operand is selected by register index, not by value.
Click a register — DEC will target it
Set pre-state value
0x000000000000000A
State transition: pre → DEC → post