HP-UX was one of the most popular operating systems to run on Itanium though?

HP was also one of the few companies to actually sell Itanium systems! They were also the last to stop selling them. They ported both OpenVMS and HP-UX to Itanium.

	▲	tyingq 5 hours ago \| parent [-]
		Well, largely because they made it difficult for customers to stay on PA-RISC, then later, because their competitors were dying off...and if you were in the market for stodgy RISC/Unix there weren't many other choices.