Can we install Unix in PC or imac?

I'm a beginner in Unix OS. I really want to know what kind of hardware I need in order to install the Unix OS.(I know Linx can be installed in both Mac & PC, but not Unix)

Thanks to let me ask such question here.

on mac you can install OS X which will be released in its final version on March 24th. Its core is called Darwin and is built on FreeBSD. FreeBSD can also be installed on PCs.

Or you can just download Darwin for free and install it on a mac, it will not have any of the gui that OS X has.