New HP

I went scrounging again today and found a new source of old computers. There I found and passed up a HP 9000 835 and a HP 9836A. BUT I did bring home a HP 9000 520 (aka HP 9020). :-) I used to think the HP 9845 was big and heavy but not any more! I don't know much about the 520 except that they were supposed to be the replacement for the HP 9845 but had developement problems and were very late getting into production and few of them were sold. I believe it has BASIC in ROM but I'm not sure. Does anyone have docs for these? It has two HP-IB cables that are connected internally and a 15 pin socket under the front edge. What are they for? I picked up a HP 9153 hard drive that was in the same box with the 520. I'm hoping that there's software for the 520 on it. Joe