Windows Server 2003 is the follow-up to Windows 2000 Server, incorporating compatibility and other features from Windows XP. Unlike Windows 2000 Server, Windows Server 2003's default installation has none of the server components enabled, to reduce the attack surface of new machines. Windows Server 2003 includes compatibility modes to allow older applications to run with greater stability. It was made more compatible with Windows NT 4.0 domain-based networking. Windows Server 2003 brought in enhanced Active Directory compatibility, and better deployment support, to ease the transition from Windows NT 4.0 to Windows Server 2003 and Windows XP Professional.
Changes to various services include those to the IIS web server, which was almost completely rewritten to improve performance and security, Distributed File System, which now supports hosting multiple DFS roots on a single server, Terminal Server, Active Directory, Print Server, and a number of other areas. Windows Server 2003 was also the first operating system released by Microsoft after the announcement of its Trustworthy Computing initiative, and as a result, contains a number of changes to security defaults and practices.
The product went through several name changes during the course of development. When first announced in 2000, it was known by its codename, "Whistler Server"; it was named "Windows 2002 Server" for a brief time in mid-2001, followed by "Windows .NET Server" and "Windows .NET Server 2003". After Microsoft chose to focus the ".NET" branding on the .NET Framework, the OS was finally released as "Windows Server 2003".
Windows Server 2003 was the first Microsoft Windows version which was thoroughly subjected to semi-automated testing for bugs with a software system called PREfast developed by computer scientist Amitabh Srivastava at Microsoft Research. The automated bug checking system was first tested on Windows 2000 but not thoroughly. Amitabh Srivastava's PREfast found 12% of Windows Server 2003's bugs, the remaining 88% being found by human computer programmers. Microsoft employs more than 4,700 programmers who work on Windows, 60% of whom are software testers whose job is to find bugs in Windows source code. Microsoft co-founder Bill Gates stated that Windows Server 2003 was Microsoft's "most rigorously tested software to date."
Microsoft later used Windows Server 2003's kernel in the development of Windows Vista.