The worst version of commercial unix available. It's not as nonstandard as AIX, but it has plenty of deficiencies to make up for that. Often referred to as HP-SUX. HP-UX sounds great at first, with things like kernel threads, but then you find out none of you current programs will port over to the damn thing without a lot of work. Plus the PA-RISC processor is a real dog. And all of their cabinets look like they were designed in 1970.