OpenVMS was what I cut my systems teeth on. This was back in the late
80s when
Unix was that unreliable OS that crashed all the time (much like
NT now), and if you wanted to get
real work done, you used a
VAX with
VMS on it.
You haven't lived until you've done systems programming on VMS. Although if you do systems programming on NT it's vaguely similar--Dave Cutler was hired by Microsoft to design the Windows NT internals, and the structures are similar.