I found a offhanded link on kottke.org: Williams Defender Information and Links. I can’t tell you how much of a defender/stargate fan I was. I mean I was a child of the arcade. Having not many friends (well none really) to hang with, the arcade gave me an escapist retreat. Oh, I had my books, but T.V. sucked. So, when the games began to emerge, so did I… (from my room). Defender was my absolute favorite. Stargate, the sequel was good, but not as good and original as defender. This page is a pretty good “info set” about the game and ROMs that are available.