Following up on that, how do you boot from different partitions?
   If i was doing an upgrade and needed to boot from the sd0b instead of sd0a,
   where does one do that?

alpha's can only boot from the start of the disk.  partitions are understood
by SRM -- it only loads the first blocks from the disk and executes them.
   
   > type ^C (control-C) before it starts loading the kernel to get to the
   > SRM prompt, which is ">>>"

to be pedantic, it really is "\n\n>>> " :-)