| Opcode/Instruction               | Op/En | 64-Bit Mode | Compat/Leg Mode | Description                                                                                                        |
| -------------------------------- | ----- | ----------- | --------------- | ------------------------------------------------------------------------------------------------------------------ |
| 0F C7 /1 CMPXCHG8B m64           | M     | Valid       | Valid           | Compare EDX:EAX with m64. If equal, set ZF and load ECX:EBX into m64. Else, clear ZF and load m64 into EDX:EAX.    |
| REX.W + 0F C7 /1 CMPXCHG16B m128 | M     | Valid       | N.E.            | Compare RDX:RAX with m128. If equal, set ZF and load RCX:RBX into m128. Else, clear ZF and load m128 into RDX:RAX. |