x86 architecture general purpose registers   traditional general purpose registers   6 3   3 2 3 1   1 6 1 5   8 7   0 RAX or R0 zero-extended EAX or R0D preserved preserved AX or R0W AH AL or R0B RCX or R1 zero-extended ECX or R1D preserved preserved CX or R1W CH CL or R1B RDX or R2 zero-extended EDX or R2D preserved preserved DX or R2W DH DL or R2B RBX or R3 zero-extended EBX or R3D preserved preserved BX or R3W BH BL or R3B RSP or R4 zero-extended ESP or R4D preserved preserved SP or R4W preserved SPL or R4B RBP or R5 zero-extended EBP or R5D preserved preserved BP or R5W preserved BPL or R5B RSI or R6 zero-extended ESI or R6D preserved preserved SI or R6W preserved SIL or R6B RDI or R7 zero-extended EDI or R7D preserved preserved DI or R7W preserved DIL or R7B   additional general purpose registers   6 3   3 2 3 1   1 6 1 5   8 7   0 R8 zero-extended R8D preserved R8W preserved R8B R9 zero-extended R9D preserved R9W preserved R9B R10 zero-extended R10D preserved R10W preserved R10B R11 zero-extended R11D preserved R11W preserved R11B R12 zero-extended R12D preserved R12W preserved R12B R13 zero-extended R13D preserved R13W preserved R13B R14 zero-extended R14D preserved R14W preserved R14B R15 zero-extended R15D preserved R15W preserved R15B   instruction pointer   6 3   3 2 3 1   1 6 1 5   8 7   0 RIP reserved EIP reserved IP