Mac OS X was developed as an entirely new, BSD-based operating system that runs on a more advanced processor (the Power PC) but which maintains backward compatibility with the Mac OS (which runs on the Motorola m68k).
The Mac OS X consists of Darwin and the Mach microkernel (an advanced kernel developed at Carnegie-Mellon University) together with Apple's proprietary Aqua GUI (which is widely regarded as the best in the industry).
Sky OS - a commercial hobbyist operating system developed by Robert Szeleney from 1996. It is mostly POSIX compliant, and comes with many of the GNU utilities, including the very highly rated GCC (GNU Compiler Collection).
Solaris - developed by Sun Microsystems for its SPARC processor and the most widely used proprietary flavor of UNIX.
Solaris was introduced as Sun OS in 1989, and it was based on BSD Unix. TRON (The Real-time Operating system Nucleus) - started by Professor Ken Sakamura of the University of Tokyo in 1984 with the goal of creating an ideal computer architecture.
TRON claims to be the world's most widely used operating system because it is embedded in a vast number and variety of electronic products.
GNU/Linux, as it is also called (because it makes extensive use of utilities and other software developed by the GNU project) is suitable for use on a wide range of platforms and is compatible with both 32 bit and 64 bit processors.
More than 200 distributions (i.e., versions) of Linux have been introduced, among the most popular of which are Red Hat, Su SE, Mandrake, Debian and Ubuntu.
Microsoft Windows - the successors to the very popular MS-DOS, it was announced in 1983, and the first version, Windows 1.0, was finally released in 1985.Darwin - an open source derivative of 4.4BSD (Berkeley Software Distribution Version 4.4) that serves as the core for the Macintosh OS X. There is also a GNU version of Darwin, which is called GNU-Darwin.Free BSD - the most popular of the BSD operating systems, accounting for approximately 80 percent of BSD installations (at least until Darwin came onto the scene).Although its overall market share is still small, Linux is the most rapidly growing of any major operating system. in 2001 as a replacement for its aging Mac OS operating system.Now commonly referred to as Mac Classic, the pioneering Mac OS was introduced with the first Macintosh computers in 1984, and it was the first commercial operating system to include a GUI.