Interactive x86-64 general-purpose register explorer covering sub-register aliases and the identity vs value distinction

Sub-register aliases — all in the same 64-bit storage

bits 63–32 upper 32 (RAX only)
bits 31–16 EAX upper
bits 15–8 AH
bits 7–0 AH (legacy)
bits 7–0 AL
RAX
bits 63–0 · all 64
EAX
bits 31–0 · low 32
AX
bits 15–0 · low 16
AH / AL
bits 15–8 / 7–0

The 16 general-purpose registers

Index 64-bit name 32-bit 16-bit 8-bit low Role / notes

Identity vs. value — write a value, watch the aliases

Pick a register Index (identity): 0
Write a value 0
RAX 0x0000000000000000
EAX 0x00000000
AX 0x0000
AH / AL 0x00 AH (bits 15–8) 0x00 AL (bits 7–0)
The register's index stays constant — only the value changes. RAX is always register #0 regardless of what's in it.