IBM minis still humming

Yesterday, I finally received the chance to examine a family of computers that has been bugging me for a while. In the mid to late 1970s, IBM introduced a family of minis designed to kill the PDP-11, or so they thought. The series/1 is a bit different, in that they are not designed to run COBOL applications in a business environment. They are also very modular, something that other IBM offerings are not. I saw about 25 of the big beasts, all humming away at thier duties, and of course, now want one (love at first sight, it happens alot with collectors). Unfortunately, I am still lacking just about all technical information about the family. Has anyone on the list ever use one of these things? What operating system did it use? Just how good (or bad, probably) are these things? Oh, sorry about repeating the modem information! William Donzelli william(a)ans.net