Mac OS X (pronounced /mæk oʊ ɛs tɛn/) is a line of
computer operating systems developed, marketed, and sold by
Apple Inc., and since 2002 has been included with all new
Macintosh computer systems. It is the successor to Mac OS 9,
the final release of the "classic" Mac OS,
which had been Apple's primary operating system since 1984.
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
early 1996. Its sixth and most recent version, Mac OS X
v10.5 is certified UNIX 03 while running on Intel
processors. The first version released was Mac OS X Server
1.0 in 1999, and a desktop-oriented version, Mac OS X
version 10.0 followed in March 2001. Releases of Mac OS X
are named after big cats; for example, Mac OS X v10.5 is
usually referred to by Apple and users as
"Leopard". The server edit