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Windows NT

Company / developer	Microsoft
Programmed in	C, C++ and Assembly language[1]
Working state	Current
Source model	Closed source / Shared source
Initial release	27 July 1993 (1993-07-27) (as Windows NT 3.1)
Latest stable release	Windows 7, Windows Server 2008 R2 NT 6.1 (Build 7601: Service Pack 1)  (February 22, 2011; 16 months ago (2011-02-22)) [±]
Latest unstable release	Windows 8 NT 6.2 (Build 8400)  (May 31, 2012; 53 days ago (2012-05-31)) [±]
Update method	Windows Update
Supported platforms	IA-32, x86-64, Alpha, MIPS, PowerPC, ARM, Itanium
Kernel type	Hybrid
Default user interface	Graphical (Windows Explorer)
License	MS-EULA
Official website	www.microsoft.com/windows/

Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement consumer versions of Windows that were based on MS-DOS. NT was the first fully 32-bit version of Windows, whereas its consumer-oriented counterparts, Windows 3.1x and Windows 9x, were 16-bit/32-bit hybrids. Windows 2000, Windows XP, Windows Server 2003, Windows Vista, Windows Home Server, Windows Server 2008, Windows 7, Windows 8 and Windows Server 2012 are members of the Windows NT family, although they are not branded using the name "Windows NT".

  Naming

It is popularly believed that Dave Cutler^[2] intended the initialism "WNT" as a pun on VMS, incrementing each letter by one. However, the project was originally intended as a follow-on to OS/2 and was referred to as "NT OS/2" before receiving the Windows brand.^[3] One of the original NT developers, Mark Lucovsky, states that the name was taken from the original target processor—the Intel i860, code-named N10 ("N-Ten").^[4] Various Microsoft publications, including a 1998 question-and-answer session with Bill Gates, reveal that the letters were expanded to "New Technology" for marketing purposes but no longer carry any specific meaning.^[5] The letters were dropped from the name of Windows 2000, though Microsoft described the product as "Built on NT technology".

  Major features

A main design goal of NT was hardware and software portability. Various versions of NT family operating systems have been released for a variety of processor architectures, initially Intel IA-32, MIPS R3000/R4000, and Alpha, with PowerPC, Itanium, AMD64 and ARM supported in later releases. The idea was to have a common code base with a custom Hardware Abstraction Layer (HAL) for each platform. However, support for MIPS, Alpha, and PowerPC was later dropped after NT 4.0. Broad software compatibility was achieved with support for several API "personalities", including Win32, POSIX,^[6] and OS/2^[7] APIs - the latter two were phased out starting with Windows XP.^[8] Partial MS-DOS compatibility was achieved via an integrated DOS Virtual Machine - although this feature is being phased out in the x86-64 architecture.^[9] NT supported per-object (file, function, and role) access control lists allowing a rich set of security permissions to be applied to systems and services. NT supported Windows network protocols, inheriting the previous OS/2 LAN Manager networking, as well as TCP/IP networking (for which Microsoft would implement a TCP/IP stack derived at first from STREAMS, then later rewritten in-house.^[10])

Windows NT 3.1 was the first version of Windows to utilize 32-bit "flat" virtual memory addressing on 32-bit processors. Its companion product, Windows 3.1, used segmented addressing and switches from 16-bit to 32-bit addressing in pages.

Windows NT 3.1 featured a core kernel providing a system API, running in supervisor mode, and a set of user-space environments with their own APIs which included the new Win32 environment, an OS/2 1.3 text-mode environment and a POSIX environment. The full preemptive multitasking kernel could interrupt running tasks to schedule other tasks, without relying on user programs to voluntarily give up control of the CPU, as in Windows 3.1 Windows applications (although MS-DOS applications were preemptively multitasked in Windows starting with Windows 1.0).

Notably, in Windows NT 3.x, several I/O driver subsystems, such as video and printing, were user-mode subsystems. In Windows NT 4, the video, server, and printer spooler subsystems were integrated into the kernel. Windows NT's first GUI was strongly influenced by (and programmatically compatible with) that from Windows 3.1; Windows NT 4's interface was redesigned to match that of the brand new Windows 95, moving from the Program Manager to the Start Menu/Taskbar design.

NTFS, a journaled, secure file system, was created for NT. Windows NT also allows for other installable file systems, and with versions 3.1 and 3.51, NT could also be installed on DOS's FAT or OS/2's HPFS file systems. Later versions could be installed on a FAT32 partition, in select cases, including Vista versions.^[11] Windows Vista and Windows 7 require a FAT32 partition to boot on an EFI based system.^[12]

  Development

Microsoft decided to create a portable operating system, compatible with OS/2 and POSIX and supporting multiprocessing, in October 1988.^[13] When development started in November 1989, Windows NT was to be known as OS/2 3.0,^[14] the third version of the operating system developed jointly by Microsoft and IBM. To ensure portability, initial development was targeted at the Intel i860XR RISC processor, switching to the MIPS R3000 in late 1989, and then the Intel i386 in 1990.^[15] Microsoft also continued parallel development of the DOS-based and less resource-demanding Windows environment, resulting in the release of Windows 3.0 in May 1990. Windows 3 was eventually so successful that Microsoft decided to change the primary application programming interface for the still unreleased NT OS/2 (as it was then known) from an extended OS/2 API to an extended Windows API. This decision caused tension between Microsoft and IBM and the collaboration ultimately fell apart. IBM continued OS/2 development alone while Microsoft continued work on the newly renamed Windows NT. Though neither operating system would immediately be as popular as Microsoft's MS-DOS or Windows products, Windows NT would eventually be far more successful than OS/2.

Microsoft hired a group of developers from Digital Equipment Corporation led by Dave Cutler to build Windows NT, and many elements of the design reflect earlier DEC experience with Cutler's VMS ^[16] and RSX-11. The operating system was designed to run on multiple instruction set architectures and multiple hardware platforms within each architecture. The platform dependencies are largely hidden from the rest of the system by a kernel mode module called the HAL (Hardware Abstraction Layer).

Windows NT's kernel mode code further distinguishes between the "kernel", whose primary purpose is to implement processor and architecture dependent functions, and the "executive". This was designed as a modified microkernel, as the Windows NT kernel was influenced by the Mach microkernel developed at Carnegie Mellon University^[17], but does not meet all of the criteria of a pure microkernel. Both the kernel and the executive are linked together into the single loaded module ntoskrnl.exe; from outside this module there is little distinction between the kernel and the executive. Routines from each are directly accessible, as for example from kernel-mode device drivers.

API sets in the Windows NT family are implemented as subsystems atop the publicly undocumented "native" API; this allowed the late adoption of the Windows API (into the Win32 subsystem). Windows NT was one of the earliest operating systems to use Unicode internally.

  Driver models

Windows NT introduced its own driver model, the Windows NT driver model, and is incompatible with older driver frameworks. With Windows 2000, the Windows NT driver model was enhanced to become the Windows Driver Model, which was first introduced with Windows 98, but was based on the NT driver model.^[18] Windows Vista added native support for the Windows Driver Foundation, which is also available for Windows XP, Windows Server 2003 and to an extent, Windows 2000.

  Releases

Windows NT 3.1 to 3.51 incorporated the Program Manager and File Manager from the Windows 3.x series. Windows NT 4.0 onwards replaced those programs with Windows Explorer (including a taskbar and Start menu), which originally appeared in Windows 95.

The first release was given version number 3.1 to match the contemporary 16-bit Windows; magazines of that era claimed the number was also used to make that version seem more reliable than a ".0" release. There were also some issues related to Novell IPX protocol licensing, which was apparently limited to 3.1 versions of Windows software.^{[citation needed]}

The NT version number is not now generally used for marketing purposes, but is still used internally, and said to reflect the degree of changes to the core of the operating system;^[30] however, for application compatibility reasons, Microsoft has kept the major version number as 6 in releases following Vista.^[31] The build number is an internal identifier used by Microsoft's developers and beta testers.

  Supported platforms

NT was written in C and C++,^[32] and is reasonably portable, although (as of 2009^[update]) only three architectures are currently supported. That said, it proved far more difficult to port applications such as Microsoft Office which were sensitive to issues such as data structure alignment on RISC processors. Unlike Windows CE which routinely runs on a variety of processors, the lack of success of RISC-based systems in the desktop market has resulted in nearly all NT deployments being on x86 architecture processors.

  32-bit platforms

In order to prevent Intel x86-specific code from slipping into the operating system by developers used to developing on x86 chips, Windows NT 3.1 was initially developed using non-x86 development systems and then ported to the x86 architecture. This work was initially based on the Intel i860-based Dazzle system and, later, the MIPS R4000-based Jazz platform. Both systems were designed internally at Microsoft.^[33]

Windows NT 3.1 was released for Intel x86 PC compatible, DEC Alpha, and ARC-compliant MIPS platforms. Windows NT 3.51 added support for the PowerPC processor in 1995, specifically PReP-compliant systems such as the IBM Power Series desktops/laptops and Motorola PowerStack series; but despite meetings between Michael Spindler and Bill Gates, not on the Power Macintosh as the PReP compliant Power Macintosh project failed to ship.

Intergraph Corporation ported Windows NT to its Clipper architecture and later announced intention to port Windows NT 3.51 to Sun Microsystems' SPARC architecture,^[34] but neither version was sold to the public as a retail product.

Only two of the Windows NT 4.0 variants (IA-32 and Alpha) have a full set of service packs available. All of the other ports done by third parties (Motorola, Intergraph, etc.) have few, if any, publicly available updates.

Windows NT 4.0 was the last major release to support Alpha, MIPS, or PowerPC, though development of Windows 2000 for Alpha continued until August 1999, when Compaq stopped support for Windows NT on that architecture; and then three days later Microsoft also canceled their AlphaNT program, even though the Alpha NT 5 (Windows 2000) release had reached RC2 (build 2128).

Microsoft announced on 5 January 2011 that the next major version of the Windows NT family will include support for the ARM architecture. Microsoft demonstrated a preliminary version of Windows (version 6.2.7867) running on an ARM-based computer at the 2011 Consumer Electronics Show.^[35]

According to Microsoft, it is a common misconception that the Xbox and Xbox 360 use a modified Windows 2000 kernel.^[36] They claim that the Xbox operating system was built from scratch but implements a subset of Windows APIs. The idea that it does, indeed, run a modified copy of the Windows kernel still persists in the community.

  64-bit platforms

Released versions of NT for Alpha were 32-bit only. The 64-bit port of Windows was originally intended to run on Itanium as well as on Alpha. Alpha hardware was accordingly used internally at Microsoft during early development of 64-bit Windows.^[37][38] This continued for some time after Microsoft publicly announced that it was cancelling plans to ship 64-bit Windows for Alpha, because Itanium hardware was not yet available for development.^[39]

As of June 2010^[update], Microsoft has released seven editions for Itanium and seventeen editions for the x64 processor architecture:

  Hardware requirements

The minimum hardware specification required to run each release of the professional workstation version of Windows NT has been fairly slow-moving until the 6.0 Vista release, which requires a minimum of 15 GB of free disk space, a 10-fold increase in free disk space alone over the previous version.

*Windows XP can be run with 64 MB of RAM. Some features require 128 MB RAM.^[53]

  See also

• Architecture of Windows NT
• Criticism of Microsoft Windows
• F6 disk
• Microsoft Windows
• NT Domain
• NTFS
• ReactOS (an open source project with the goal of providing binary- and device driver-level compatibility with Windows NT)
• Windows NT Startup Process
• Windows Preinstallation Environment
• Microsoft Servers
• Windows Embedded

  References

  External links

• Official Page
• Windows NT and VMS: The Rest of the Story, discussion of ancestry of NT by Mark Russinovich
• A Brief History of the Windows NT Operating System a Microsoft PressPass Fact Sheet