The EUI-48™ node address consists of a 24-bit OUI and a 24-bit EI, while the the EUI-64™ consists of either a 24 or 36 bit OUI and a 40 or 28-bit EI respectively. The EIs in both cases are assigned by the organization. Microchip’s MAC address chips come with uniquely pre-programmed and write-protected 48-bit EUI addresses.