From HP-UX 10.20 onwards swap is implemented somewhat differently which is why the old rules do not apply. From 10.20 onwards you have a true demand paged memory model, so when things execute they have two types of pages, retrievable and anonymous, retreivable pages are related to things like files on disk and these will no longer be allocated against your swap device, as they can simply be retreived from disk if they ever get kicked from memory, now your anonymous pages are the interesting ones, they cannot be retreived and you must therefore allocate some swap for them, now we have the awkward question of what is swap, well it is no longer your swap device, it is normal demand paged memory, so the swap page will be allocated initially against memory and if accessed enough will remain there, however if the machine starts to become short of memory pages get flushed from the memory cache according to the same rules as any other page and if the page had not been accessed it will be put on the freelist, if it remains there long enough without a page reclaim, it will be re-used, at this point it will be written to the swap device.
This is why you hear statements like if you have enough memory you do not need any swap space, this can be true these days, the rule of 4 came from the days when an entire process, plus all its stack, etc must have a one to one relationship with space on the swap device, this has not been true for a number of years now.
Hope this helps.
