mov eax, 1

Basic mov immediate instruction.

Output:

b8 01 00 00 00
^^ ^^^^^^^^^^^
1  2

1. Opcode
2. Immediate value: 1 in little endian

Opcode bits:

1 0 1 1 1 0 0 0
^^^^^^^^^ ^^^^^
1         2

1. What to do.
2. Where to move to. 000 is eax.

Intel documentation says:

• Opcode: B8 + rd id.

  +rd says that the 3 bits at the end are the destination register.

  id says that a double word immediate follows.

• Op/En: OI.

  The "Instruction Operand Encoding" table for mov and OI says:

  Operand 1: opcode + rd (w) Operand 2: imm8/16/32/64