Basically the same machine was also sold as the 3b1; the difference between the 7300 and the 3b1 is that the 3b1 has room for a taller hard disk drive. I think the OS would best be characterized as SVR2 with the addition of the 4.1bsd VM system ("real" SVR2 had no demand paged VM) and the further addition of its own unique approach to shared libraries. It's definitely not SVR3; no "STREAMS".