Stephen Harris wrote:
In older BSD systems (eg around SunOS 4 times or before) swap space was utilised oddly; all memory was allocated from swap, so you needed _at least_ <physmem> of swap just to use all your real memory! So if you added <physmem> of swap then your total virtual memory size was still only <physmem>. No help! So the rule of thumb came along that said "swap = 2*<physmem>" and that gave you a VM of 2*<physmem>.
<old codger hat> this was also how early IBM System/370 DOS/VS worked... the swap space (which was contiguous cylinders of the disk, btw) was mapped 1:1 to virtual memory address space </old codger hat>
now, on late model Solaris, 'swap' is also used as tmpfs, which /tmp and /var/run utilizes by default, so you definitely want to allocate sufficient swap space for this at least, regardless of how large your physical memory is.