Register Names

The following is a list of register names for x86-64 assembly

Base Label	Labels for Lower n-bits of a Register				Additional Info
	8-bit	16-bit	32-bit	64-bit
a	al	ax	eax	rax	a for accumulator
b	bl	bx	ebx	rbx	b for base
c	cl	cx	ecx	rcx	c for counter
d	dl	dx	edx	rdx	d for data
si	sil	si	esi	rsi	source index
di	dil	di	edi	rdi	destination index
bp	bpl	bp	ebp	rbp	stack base pointer
sp	spl	sp	esp	rsp	stack pointer (end position of runtime stack)
r8	r8b	r8w	r8d	r8
r9	r9b	r9w	r9d	r9
r10	r10b	r10w	r10d	r10
r11	r11b	r11w	r11d	r11
r12	r12b	r12w	r12d	r12
r13	r13b	r13w	r13d	r13
r14	r14b	r14w	r14d	r14
r15	r15b	r15w	r15d	r15

Additional Notes:

In the 8-bit column for the first 8 register, l stands for low or lower. You can actually address the upper 8-bits of the lower 16-bits with h.

In the 4 central columns for registers r8 through r15, the letter b stands for byte (8-bits being addressed), w for word (there was a time where most machines had a word size of 16 bits, that is, this is a legacy holdover from that time), and d for double word (32-bits is twice 16-bits).

There are some additional registers outside of the 16 mentioned above, that is the ip, or instruction pointer register, and then the status flags.