With Irix it means overcommitment of virtual memory, which can lead to stability issues. With SunOS/Solaris it means delaying paging decisions needed with the performance penalties I described earlier in stressful situations. That is just a design choice with pros and cons.
I was not referring to speed
I am not confusing anything. I was talking about pseudoswap, where virtual memory that gets reserved actually gets preallocated. Pages in pseudoswap will not be paged out.
It is not incorrect (see above). There is a big difference here.
Well I have witnessed it.
There is for pseudoswap. For every other system that does not have enough physical paging space available the effect is similar, because virtual memory is limited and this typically means a large part of your RAM never gets used.

---------- Post updated at 03:18 PM ---------- Previous update was at 02:43 PM ----------

I agree the discussion is becoming a bit broad here, HP-UX was not even directly relevant to the discussion but served as an example and we fanned out from there

My point was simply that if you do not have enough physical swap space, part of internal memory will never get used, simply because processes will not be allowed to start due to insufficient virtual memory. If you have more swap space, say equal to the amount if internal memory then this allows you to load more processes but typically this will still not lead to a situation where actual paging does occur. If you keep adding more swap space then this allows you to continue loading up to the point where actual paging does start to occur. A little bit of paging does not hurt performance, but obviously if the pageout rate starts to become significant then this will gradually start to slow down the system. But you can simply control this situation by running fewer programs.

At least you have a choice then, which is not the case if you do not have enough swap space.

S.