Most likely this is what you have as it was standard on the first few 
models of PowerMac's.

note: the 6400's and 6500's like you have had a modem or ethernet as 
OEM.

Michael

On Jul 14, 2004, at 8:52 PM, Gerald Combs wrote:

> The special interface was the "AAUI" (Apple AUI).  Dunno why they 
> didn't
> just use the IEEE standard AUI like everyone else at the time.  If your
> friend's Mac has an AAUI interface, you can get a transceiver for $4,
> according to Froogle:
>
>     http://www.smalldog.com/product/37076/atfgc
>
> Better hurry, though.  There are only 282 of these rare and valuable
> artifacts left in stock.