An operating system is a computer program that manages the hardware and software resources of a computer. At the foundation of all system software, an operating system performs basic tasks such as controlling and allocating memory, prioritizing system requests, controlling input and output devices, facilitating networking, and managing files. It also may provide a graphical user interface for higher level functions. It forms as a platform for other software to be accessed and ran.

Windows XP is a line of proprietary operating systems developed by Microsoft for use on general-purpose computer systems, including home and business desktops, notebook computers, and media centers. The letters "XP" stand for experience. Codenamed "Whistler" after Whistler, British Columbia, as many Microsoft employees skied at the Whistler-Blackcomb ski resort during its development, Windows XP is the successor to both Windows 2000 and Windows Me, and is the first consumer-oriented operating system produced by Microsoft to be built on the Windows NT kernel and architecture.

Windows XP was first released on October 2001, and over four hundred million copies are in use, according to a January 2006 estimate by an IDC analyst. It is succeeded by Windows Vista, which was released to the general public in January 2007.

Windows XP is known for its improved stability and efficiency over previous versions of Microsoft Windows. It presents a significantly redesigned eye catching user interface, a change Microsoft promoted as more user-friendly than previous versions of Windows. New software management capabilities were introduced to avoid any undesired issues that occurred within the previous systems.

It is also the first version of Windows to use product activation to combat software piracy, a restriction that did not sit well with some users and privacy advocates. Windows XP has also been criticized by some users for security vulnerabilities, tight integration of applications such as Internet Explorer and Windows Media Player.

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-like 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 (version 10.0) following in March 2001. Since then, four more distinct "end-user" and "server" editions of Mac OS X have been released, the most recent being Mac OS X (version 10.4), which was first made available in 2005.

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 workgroup 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.

Unix is a computer operating system originally developed between the 1960s and 1970s by a group of AT&T employees at Bell Labs. Today's Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations.

The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX®"

During the late 1970s and early 1980s, Unix's influence in academic circles led to large-scale adoption of Unix by commercial startups, the most notable of which is Sun Microsystems. Today, in addition to certified Unix systems, Unix-like operating systems such as Linux, Mac OS X and BSD derivatives are commonly encountered.

Linux is a Unix-like computer operating system family that uses the Linux kernel. A Linux system which includes system utilities and libraries from the GNU Project is sometimes referred to as GNU/Linux.

Most development from 1984 to 1991 was done by the GNU project. After 1991, the Linux kernel developers began working on it as well as other enthusiasts. From the late-90s onward Linux also gained the support of corporations such as IBM, Sun Microsystems, Hewlett-Packard, and Novell, Inc.

Linux is a prominent example of free software and of open source development. Its underlying source code is available for anyone to use, modify, and redistribute freely, and in some instances the entire operating system consists of free/open source software.