The "Original" IEEE formats are essentially a two-byte header followed by an embedded mac address contains the OUI. The first 2 bytes are either hex 10:00 or 2x:xx followed by the 3-byte OUI and 3 bytes for a vendor-specified serial number. The difference between NAA 1 format and NAA 2 format is merely the presence of either a zero pad or an extra 3 nibbles of vendor information. The Registered IEEE formats dispense with padding and place the OUI immediately after the NAA. The OUI is no longer considered to be part of a MAC address. For NAA 5 format, this leaves 9 contiguous nibbles for a vendor-defined value. This is the same format used by the companion NAA 6 format, the only difference being a 16-byte number space is assumed, rather than an 8-byte number space. This leaves a total of 25 contiguous nibbles for vendor-defined values.