Hardware address is the unique fingerprint of your computer. We need this to assign a specific serial number that will not work on any other computer except yours.

A hardware address is also known as Ethernet ID, Airport ID, MAC address and a few other names.

-In OS8 or 9, you can determine the hardware address from the TCP/IP control panel. Go under the Apple menu to Control Panels. Choose TCP/IP from the list. When TCP/IP is open, go under the File menu to Get Info. The hardware address will be displayed in the dialog box.

-In OSX, you can determine the hardware address from the System Preferences dialog box:

Click on Network from within the System Preferences dialog box:

Choose the connection you're using, double click it:

For Ethernet:

For Airport: