Bitsavers has an interesting paper on PA-RISC 2.0 (the jump to 64 bits). It's got a high-level introduction, and then all the actual details.

https://bitsavers.org/pdf/hp/pa-risc/PA_RISC_2.0_Architectur... (2MB file)

Having briefly worked at HP on the IA64 effort IIRC the PA-RISC chips fabbed at Intel were the side-effect of the Itanium agreement. HP was owed a certain volume of chips and since Merced was very delayed they had to make those chips for HP.

Unfortunely most of the HP-UX documentation I used to browse regularly is now gone from HP website, at least from public pages, lots of broken links even when we manage to find some old PDFs.

I guess, it might be support/partners eyes only nowadays.

> PA-RISC Performance and History

Itanium is not PA-RISC. The article is thin.

It doesn't really claim that though, does it? I thought it was clear it was a follow on from PA-RISC, though I may be filtering it through my own brain.