Re: AC Alpha....
" The first fact convinced Compaq to switch from Alpha to Itanium"
Compaq switched from Alpha to Itanium because Intel had made it clear that the Compaq/Intel "special relationship" (re x86) was at risk unless CPQ did as they were told. This was around the time when a 64bit x86 was still impossible (according to Intel) and IA64 was still going to be "industry standard 64bit".
The HP-UX market was an HP-UX market. It wasn't specifically a PA-RISC market, and it isn't specifically an IA64 market. People largely continue to buy HP-UX *despite* IA64, not *because* of IA64.
Ditto VMS. It was (and is) a VMS market, not an IA64 market. It was VMS that mattered when it was on VAX (though VAX was relatively unique in the early years), and it was VMS that mattered when it was Alpha, and the same still goes for IA64. People largely continue to buy VMS *despite* IA64, not *because* of IA64.
Customers of HP-UX and VMS have little hardware reason to buy IA64, IA64 does little that can't already be done on an AMD64, and if/when those OSes become available on a subset of AMD64-based Proliant (check out the cores and memory on a high end Proliant), customers will continue to buy those OSes.
VMS and HP-UX both have stuff that is unique to those OSes and provides businesses with some kind of advantage. What does IA64 have that is unique to it which is an *advantage* to the customer, the software developer, the system designer? IA64 has plenty which is a *disadvantage*.
Anyways, readers don't need to take my word for it, they could ask (or look at) the customers, software developers, etc whose investment is in a multi-platform OS such as Linux or Windows. Folks who can choose their hardware platform are not choosing IA64, whatever Intel may once have said about "industry standard 64bit".
The IA64 story is only going one way;the same way as Alpha (albeit perhaps for slightly different reasons).