Rear disk caliper question

Hello,

I have a 94 Saturn SC2 with rear disk breaks, I need to change the pads on
them, when I pulled the caliper off I tried to push the piston back in and
it would not move, I then tried with a clamp and it still would not move.
Yes the emergancy break was off. but that did get me thinking that maybe
because of the emergancy break that maybe there was something I am missing.
on rear drums there is the adjuster that automaticaly ajusts itself as the
pads wear and needs to be adjusted when you replace the break shoes, so my
question is is this the same with rear disk's or is the piston just siezed
and I have to replace it?

thank you
Brent