Sizes

x86-64.

Size	Intel keyword	GAS suffix / examples
1 byte	byte	b (movb, addb); registers al, bl, …
2 bytes (16-bit “word”)	word	w (movw); ax, bx, …
4 bytes (32-bit “double word”)	dword	l (movl); eax, ebx, …
8 bytes (64-bit “quad word”)	qword	q (movq); rax, rbx, …
16 bytes	oword / xmmword	SSE / AVX vector
32 bytes	ymmword	AVX2 vector
64 bytes	zmmword	AVX-512 vector

ARM64.

Suffix	Size
b	byte (1 B); ldrb, strb
h	half-word (2 B); ldrh, strh
w (no suffix, w-prefixed register)	word (4 B); ldr w0, ...
x-prefixed register	dword (8 B); ldr x0, ...

References

• Registers for the register sizes and aliases.

• Signed vs unsigned for the sign-handling difference between same-size operations.