| 64 bits | 32 bits | 16 bits | 8 bits |
|---|---|---|---|
| rax | eax | ax | al |
| rbx | ebx | bx | bl |
| rcx | ecx | cx | cl |
| rdx | edx | dx | dl |
| rsi | esi | si | sil |
| rdi | edi | di | dil |
| rbp | ebp | bp | bpl |
| rsp | esp | sp | spl |
| r8 | r8d | r8w | r8b |
| r9 | r9d | r9w | r9b |
| r10 | r10d | r10w | r10b |
| r11 | r11d | r11w | r11b |
| r12 | r12d | r12w | r12b |
| r13 | r13d | r13w | r13b |
| r14 | r14d | r14w | r14b |
| r15 | r15d | r15w | r15b |