Hello guys, I searched the Web but did find useful matters that exactly answer these questions: 1- In Windows we have 7, 8.1, 10 etc. in Linux, Ubuntu, Redhat etc. but what about the Unix? Is there any specific Unix OS for installing on a machine? 2- When someone says "my OS is Unix" what does he/she mean by that? 3- How to download and install a Unix OS? Is it free or not? Thanks.