Mac OS X = UNIX? [duplicate]

Yes.

Indeed 10.5 and 10.6 are Unix (tm) certified which linux is not.

To be more specific, Mac OS X is built on Darwin---a derivative of BSD---running on a Mach microkernel.

Mac OS X is based on the Berkeley Software Distribution. BSD is Unix.

Indeed it is:

Mac OS X, whose "X" represents the Roman numeral for "10" and is a prominent part of its brand identity, is a Unix-based operating system, built on technologies developed at NeXT >between the second half of the 1980s and Apple's purchase of the company in late 1996. Its sixth release Mac OS X v10.5 "Leopard" gained UNIX 03 certification while running > on Intel processors.

From: http://en.wikipedia.org/wiki/Mac_OS_X

As another poster stated it's also Unix certified: http://www.opengroup.org/openbrand/register/brand3555.htm

Mac OS X is a genetic UNIX (being a descendant of NEXTSTEP and ultimately BSD, a genetic UNIX).

It's also a UNIX-like OS (being UNIX-like).

See the relationship to UNIX and Linux here:

http://www.netneurotic.de/mac/unix/timeline.html

Note that Linux is UNIX-like but no genetic or trademark UNIX. Mac OS X is both a trademark and a genetic UNIX.