MAC addresses

Can anyone please describe the MAC address on a 5/05 processor with respect to its ethernet port?

MAC defined

Short for Media Access Control address, a hardware address that uniquely identifies each node of a network. In IEEE 802 networks, the Data Link Control (DLC) layer of the OSI Reference Model is divided into two sublayers: the Logical Link Control (LLC) layer and the Media Access Control (MAC) layer. The MAC layer interfaces directly with the network media. Consequently, each different type of network media requires a different MAC layer.
On networks that do not conform to the IEEE 802 standards but do conform to the OSI Reference Model, the node address is called the Data Link Control (DLC) address

What the MAC ID does for the SLC-5/05 controller is that it uniquely identifies the controller on an Ethernet network. Every individual Ethernet interface ever made (like an SLC daughterboard or the NIC card in your computer) has a unique MAC ID.

When you're planning on using "BOOTP" protocol to assign IP addresses to controller in your network, the MAC ID is how the BOOTP server can identify specific SLC-5/05 controllers and set them up with their IP addresses.