Examples of operating systems

Microsoft Windows

Microsoft Windows is a family of proprietary operating systems that originated as an add-on to the older MS-DOS operating system for the IBM PC. Modern versions are based on the newer Windows NT kernel that was originally intended for OS/2. Windows runs on x86, x86-64 and Itanium processors. Earlier versions also ran on the DEC Alpha, MIPS, Fairchild (later Intergraph) Clipper and PowerPC architectures (some work was done to port it to the SPARC architecture).

As of June 2008, Microsoft Windows holds a large amount of the worldwide desktop market share. Windows is also used on servers, supporting applications such as web servers and database servers. In recent years, Microsoft has spent significant marketing and research & development money to demonstrate that Windows is capable of running any enterprise application, which has resulted in consistent price/performance records (see the TPC) and significant acceptance in the enterprise market.

The most widely used version of the Microsoft Windows family is Windows XP, released on October 25, 2001.

In November 2006, after more than five years of development work, Microsoft released Windows Vista, a major new operating system version of Microsoft Windows family which contains a large number of new features and architectural changes. Chief amongst these are a new user interface and visual style called Windows Aero, a number of new security features such as User Account Control, and a few new multimedia applications such as Windows DVD Maker. A server variant based on the same kernel, Windows Server 2008, was released in early 2008.

Windows 7 is currently under development; Microsoft has stated that it intends to scope its development to a three-year timeline, placing its release sometime at the end of 2009.

Unix and Unix-like operating systems

Ken Thompson wrote B, mainly based on BCPL, which he used to write Unix, based on his experience in the MULTICS project. B was replaced by C, and Unix developed into a large, complex family of inter-related operating systems which have been influential in every modern operating system (see History).

The Unix-like family is a diverse group of operating systems, with several major sub-categories including System V, BSD, and Linux. The name "UNIX" is a trademark of The Open Group which licenses it for use with any operating system that has been shown to conform to their definitions. "Unix-like" is commonly used to refer to the large set of operating systems which resemble the original Unix.

Unix-like systems run on a wide variety of machine architectures. They are used heavily for servers in business, as well as workstations in academic and engineering environments. Free software Unix variants, such as GNU, Linux and BSD, are popular in these areas.

Market share statistics for freely available operating systems are usually inaccurate since most free operating systems are not purchased, making usage under-represented. On the other hand, market share statistics based on total downloads of free operating systems are often inflated, as there is no economic disincentive to acquire multiple operating systems so users can download multiple systems, test them, and decide which they like best.

Some Unix variants like HP's HP-UX and IBM's AIX are designed to run only on that vendor's hardware. Others, such as Solaris, can run on multiple types of hardware, including x86 servers and PCs. Apple's Mac OS X, a hybrid kernel-based BSD variant derived from NeXTSTEP, Mach, and FreeBSD, has replaced Apple's earlier (non-Unix) Mac OS.

Unix interoperability was sought by establishing the POSIX standard. The POSIX standard can be applied to any operating system, although it was originally created for various Unix variants.

Mac OS X

Mac OS X is a line of proprietary, graphical operating systems developed, marketed, and sold by Apple Inc., the latest of which is pre-loaded on all currently shipping Macintosh computers. Mac OS X is the successor to the original Mac OS, which had been Apple's primary operating system since 1984. Unlike its predecessor, Mac OS X is a UNIX operating system built on technology that had been developed at NeXT through the second half of the 1980s and up until Apple purchased the company in early 1997.

The operating system was first released in 1999 as Mac OS X Server 1.0, with a desktop-oriented version (Mac OS X v10.0) following in March 2001. Since then, five more distinct "end-user" and "server" editions of Mac OS X have been released, the most recent being Mac OS X v10.5, which was first made available in October 2007. Releases of Mac OS X are named after big cats; Mac OS X v10.5 is usually referred to by Apple and users as "Leopard".

The server edition, Mac OS X Server, is architecturally identical to its desktop counterpart but usually runs on Apple's line of Macintosh server hardware. Mac OS X Server includes work group management and administration software tools that provide simplified access to key network services, including a mail transfer agent, a Samba server, an LDAP server, a domain name server, and others.