How do I interpet this x86_64 assembly opcode?

Question

Looking at some assembly code for x86_64 on my Mac, I see the following instruction:

48 c7 c0 01 00 00 00  movq    $0x1,%rax

But nowhere can I

Answer 1

Actually, mov is 0xc7 there; 0x48 is, in this case, a long mode REX.W prefix.

Answering also the question in comments: 0xc0 is b11000000. Here you can find out that with REX.B = 0 (as REX prefix is 0x48, the .B bit is unset), 0xc0 means "RAX is first operand" (in Intel syntax; mov rax, 1, RAX is first, or, in case of mov, output operand). You can find out how to read ModR/M here.