> For example, add eax, 512 translates to 05 00 02 00 00.

> The first byte (05) is an opcode specifically representing adding the EAX register to a 16-bit number. The remaining bytes are 512 (0x200) in little-endian byte order.

That explains only the first 3 of the 5 bytes in the instruction. What are the remaining 00s for? Did he perhaps mean that the opcode is for adding EAX to a 32-bit number?