my main server is an ultra10/440 running 32 bit kernel. my router is an ultra1 (for now) running a 32 bit kernel... all my other ultrasparcs run 64 bit kernels tho. you can actually build a 32 bit kernel, install a bootblock/ofwboot and move the disk from the ss20 to the U1/U2. :-) i've done this, and back again.