10.20 parisc (very old)
11.00 parisc (old)
11iv1=11.11 parisc (actual)
11iv2=11.23 itanium (actual)

There are also Operating Environment (=base OS+add-on such
OnlineJFS,Serviceguard,...):
OE Foundation (base OS)
OE Enterprise (base OS+OnlineJFS+...)
OE Mission Critical (base OS+OnlineJFS+serviceguard+wlm+...)

Note that these OE accept to be installed only on servers, not wks (OE
Technical).