Hi
Yes, the hardware platform is special for unix and the linux is designed for PC which is popular used, also linux is free. The different is little between the Unix and linux, if u want to learning the Unix/linux, I think the book: UNIX: THE TEXTBOOK (author:Syed Mansoor Sarwar ... ) is helpful for u.
Linux was designd to be like UNIX, linux command produce the same output as the UNIX commands , but the internal implementation of them may differ.
The difference between linux & unix is that linux is free and open source but UNIX is commercial.