The "X" in Mac OS X, which is read aloud as "Mac Oh Ess Ten," comes from roman numerals. Mac OS X first came out in 2001, and is completely different than the Mac OS that it replaced. Mac OS X is a UNIX OS that is based on NEXTSTEP, an older OS that Apple bought and turned into Mac OS X. Mac OS X and NEXTSTEP have a background in a kind of UNIX called BSD (more specifically FreeBSD and NetBSD). The core of Mac OS X is an open source OS called Darwin, but Darwin cannot run Mac OS X software.
Mac OS X releases are named after kinds of "big cats" and have a version number that starts with 10. The newest version of Mac OS X is called "Snow Leopard" and is version 10.6. It was released on August 28, 2009. The version before that was called "Leopard".
Link-http://thepiratebay.org/torrent/4029716/Mac_OS_9.0.4_International_English__retail_version