Hmm, hopefully this answers your question or points you in the right direction at least.

For HP-UX, iv seen a thread or two about this and also you may wanna check HPs website and also IBM has a few things about theres on the ibm.com site, as for sun they to have a website with information but i think what you mean is a non biased opinion.

HP-UX:

http://www.hp.com/products1/unix/operating/

this has a good amount of info including what playforms and things it runs on and also some good info to read about.

Sun's website should have something similar and also me supporting IBM (hey they made the first PC and allowed others to use the idea so we have mroe than one brand name of PC) and i go to IBM.com once ina while and they have a lot of info, id just check there websites and google the three types you were curiouse about and see what pops up, also if i find some better sites to go over it ill list them here and more info if i can find it, hope it helps