Using Second Hard Drive

Gentlemen:
I would like to use the hard drive from my old blown computer in my
present computer. The old one has lots of good programs which I'd
like to get at from time to time. Right now I have to unplug the
newer HD and connect the old HD every time I need the old data. Can
someone suggest how I can run either one? There are two sets of
connectors available.
Thanks for your comments.
Jack C.