Windows NT

Windows NT
Windows NT
Windows NT logo.svg
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; 8 months ago (2011-02-22)) [+/−]
Latest unstable release Windows 8
NT 6.2 (Build 8102)
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

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, and Windows 7 are effectively Windows NT, although they are not branded using that name.

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 named NT OS/2 before receiving the Windows brand.[3] One of the original OS/2 3.0 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]


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 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[16], 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.[17] 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.


Windows NT releases
Version Marketing name Editions Release date RTM build
NT 3.1 Windows NT 3.1 Workstation (named just Windows NT), Advanced Server 27 July 1993 528
NT 3.5 Windows NT 3.5 Workstation, Server 21 September 1994 807
NT 3.51 Windows NT 3.51 Workstation, Server 30 May 1995 1057
NT 4.0 Windows NT 4.0 Workstation, Server, Server Enterprise Edition, Terminal Server, Embedded 29 July 1996 1381
NT 5.0 Windows 2000 Professional, Server, Advanced Server, Datacenter Server, Advanced/Datacenter Server Limited Edition 17 February 2000 2195
NT 5.1 Windows XP Home, Professional, 64-bit Edition, Media Center (original, 2003, 2004 & 2005), Tablet PC (original and 2005), Starter, Embedded, Home N, Professional N 25 October 2001 2600
NT 5.1 Windows Fundamentals for Legacy PCs N/A 8 July 2006 2600
NT 5.2 Windows XP 64-bit Edition Version 2003[18] 28 March 2003 3790
NT 5.2 Windows Server 2003 Standard, Enterprise, Datacenter, Web, Storage, Small Business Server, Compute Cluster 24 April 2003 3790
NT 5.2 Windows XP Professional x64 Edition 25 April 2005 3790
NT 5.2 Windows Server 2003 R2 Standard, Enterprise, Datacenter, Web, Storage, Small Business Server, Compute Cluster 6 December 2005 3790
NT 5.2 Windows Home Server N/A 16 July 2007 3790
NT 6.0 Windows Vista Starter, Home Basic, Home Premium, Business, Enterprise, Ultimate, Home Basic N, Business N Business: 30 November 2006
Consumer: 30 January 2007
NT 6.0 Windows Server 2008 Foundation, Standard, Enterprise, Datacenter, Web Server, HPC Server, Itanium-Based Systems[19] 27 February 2008 6001
NT 6.1[20] Windows 7 Starter, Home Basic, Home Premium, Professional, Enterprise, Ultimate[21] 22 October 2009[22] 7600
NT 6.1[20] Windows Server 2008 R2 Foundation, Standard, Enterprise, Datacenter, Web Server, HPC Server, Itanium-Based Systems 22 October 2009[23] 7600
NT 6.2[24] Windows 8 TBA TBA TBA
TBA Windows Server 8 TBA TBA TBA

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.[25] The build number is an internal identifier used by Microsoft's developers and beta testers.

Supported platforms

NT was written in C and C++,[26] and is reasonably portable, although (as of 2009) 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.[27]

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,[28] 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.[29]

According to Microsoft, it is a common misconception that the Xbox and Xbox 360 use a modified Windows 2000 kernel.[30] 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.[31][32] 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.[33]

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

Itanium editions x64 editions
  1. Windows 2000 Advanced Server Limited Edition[34]
  2. Windows 2000 Datacenter Server[34]
  3. Windows XP 64-Bit Edition[35]
  4. Windows Server 2003 Enterprise[36]
  5. Windows Server 2003 Datacenter[36]
  6. Windows Server 2008 for Itanium-Based Systems[37]
  7. Windows Server 2008 R2 for Itanium-Based Systems[38]
  1. Windows XP Professional x64 Edition[39]
  2. Windows Server 2003 Standard x64 Edition[39]
  3. Windows Server 2003 Enterprise x64 Edition[39]
  4. Windows Server 2003 Datacenter x64 Edition[39]
  5. Windows Vista Home Basic x64 Edition
  6. Windows Vista Home Premium x64 Edition
  7. Windows Vista Enterprise x64 Edition
  8. Windows Vista Ultimate x64 Edition
  9. Windows Server 2008 Web Server x64 Edition
  10. Windows Server 2008 Standard x64 Edition
  11. Windows Server 2008 Enterprise x64 Edition
  12. Windows Server 2008 Datacenter x64 Edition
  13. Windows 7 Home Basic x64 Edition
  14. Windows 7 Home Premium x64 Edition
  15. Windows 7 Professional x64 Edition
  16. Windows 7 Enterprise x64 Edition
  17. Windows 7 Ultimate x64 Edition

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 NT desktop (x86) minimum hardware requirements
NT version CPU RAM Free disk space
NT 3.1
NT 3.1 Advanced Server
386, 25 MHz 12 MB
16 MB
90 MB
NT 3.5 Workstation
NT 3.5 Server
386, 25 MHz 12 MB
16 MB
90 MB[40]
NT 3.51 Workstation
NT 3.51 Server
386, 25 MHz 12 MB
16 MB
90 MB[40]
NT 4.0 Workstation
NT 4.0 Server
486, 25 MHz 12 MB
16 MB
124 MB[41]
2000 Professional
2000 Server
Pentium, 133 MHz 32 MB
128 MB
650 MB[42]
XP Pentium, 233 MHz 64 MB* 1.5 GB[43]
Server 2003 Pentium, 133 MHz 128 MB 1.5 GB[42]
Vista Pentium III, 800 MHz 512 MB** 15 GB[44]
7 Pentium III, 1 GHz 512 MB** 16 GB[45]

*Windows XP can be run at 64 MB RAM. Some features require 128 MB RAM.[46]

**Windows Vista and 7 can be run from 512 MB but Microsoft recommends 1 GB.[47]

See also


  1. ^ Lextrait, Vincent (January 2010). "The Programming Languages Beacon, v10.0". Retrieved 4 January 2010. 
  2. ^ Zachary, G. Pascal (1994). Show Stopper!: The Breakneck Race to Create Windows NT and the Next Generation at Microsoft. Free Press. ISBN 978-0029356715. 
  3. ^ "Microsoft Windows NT OS/2 Design Workbook". Retrieved 2008-11-15. 
  4. ^ "Paul Thurrott's History of Windows Server 2003: The Road To Gold". 
  5. ^ Gates, Bill (1998-06-05). "Q&A: Protecting children from information on the Internet". Retrieved 2005-06-26. 
  6. ^ "Paul Thurrott's SuperSite for Windows". Retrieved 2010-11-24. 
  7. ^ "Chapter 28 - OS/2 Compatibility". Microsoft. Retrieved 2010-11-24. 
  8. ^ "POSIX and OS/2 are not supported in Windows XP or in Windows Server 2003". 2007-11-05. Retrieved 2010-11-24. 
  9. ^ "x64 editions deployment". Retrieved 2010-11-24. 
  10. ^ Barr, Adam Microsoft, TCP/IP, Open Source, and Licensing, Kuro5hin, June 19, 2001. Retrieved October 3, 2010.
  11. ^ "File Systems". Retrieved 2010-11-24. 
  12. ^ "UEFI Support and Requirements for Windows Operating Systems". 2009-05-13. Retrieved 2010-11-24. 
  13. ^ Dave Cutler's preface to Mark Russinovich, David A. Solomon. Microsoft Windows Internals, (Fourth Edition), Microsoft Press. ISBN 0-7356-1917-4
  14. ^ Andrew Pollack (1991-07-27). "Microsoft Widens Its Split With I.B.M. Over Software - New York Times". New York Times. Retrieved 2008-09-02. 
  15. ^ Paul Thurrott (2003-01-24). "Windows Server 2003: The Road To Gold". Retrieved 2010-01-05. 
  16. ^ "Supporting Windows NT and 2000 Workstation and Server". Prentice Hall. 1999-12-01. ISBN 9780130830685. Retrieved 2011-08-29. 
  17. ^ "NT Drivers - FAQ - WDM". 
  18. ^ "Microsoft Releases Windows XP 64-Bit Edition Version 2003 to Manufacturing". March 2003. Retrieved 2008-01-14. 
  19. ^ "Windows Server 2008: Overview of Editions". Retrieved 2009-05-18. 
  20. ^ a b "Operating System Versioning". Microsoft Developer Network. Microsoft. 2009-05-20. Retrieved 2009-07-06. 
  21. ^ LeBlanc, Brandon (2009-02-04). "A closer look at the Windows 7 SKUs". Retrieved 2009-02-05. 
  22. ^ Rothman, Wilson (2009-06-02). "Windows 7 To Be Released October 22". Gizmodo. Retrieved 2009-06-06. 
  23. ^ "Windows Server 2008: Product Roadmap". Retrieved 2009-05-18. 
  24. ^
  25. ^ Russinovich, Mark; Solomon, David (2001-12), Windows XP: Kernel Improvements Create a More Robust, Powerful, and Scalable OS, archived from the original on 2003-04-23,, retrieved 2006-12-19 
  26. ^ "Windows NT System Overview". Retrieved 2010-11-24. 
  27. ^ Lucovsky, Mark (2000-08-09). "Windows: A Software Engineering Odyssey". Retrieved 2006-11-02. 
  28. ^ "Intergraph Announces Port of Windows NT to SPARC Architecture". The Florida SunFlash. 1993-07-07. 
  29. ^ Microsoft demonstrates early build of Windows 8
  30. ^ Shaheen Gandhi. "Xbox Team: The Xbox Operating System". Retrieved 2008-05-29. 
  31. ^ Paul Thurott (December 1999). "The Road to Gold: The development of Windows 2000 Reviewed". Retrieved 2008-01-05. 
  32. ^ Raymond Chen (August 2008). "Windows Confidential". 
  33. ^ Paul Thurott (June 2000). "Windows 2000 Reportedly Returning to Alpha Platform". Retrieved 2008-01-05. 
  34. ^ a b Fontana, John (30 August 2001). "Microsoft Ships 64-Bit Windows for Itanium". PC World. PCWorld Communications, Inc. Retrieved 14 October 2011. 
  35. ^ "Microsoft Windows XP 64-Bit Edition". Microsoft TechNet. Microsoft Corporation. 15 August 2001. Retrieved 14 October 2011. 
  36. ^ a b "Comparison of Windows Server 2003 Editions". Microsoft TechNet. Microsoft Corporation. Retrieved 14 October 2011. 
  37. ^ "Windows Server 2008 for Itanium-Based Systems Feature Support". Microsoft TechNet. Microsoft Corporation. Retrieved 14 October 2011. 
  38. ^ "Windows Server 2008 R2 for Itanium-Based Systems". Windows Server Editions. Microsoft Corporation. Retrieved 14 October 2011. 
  39. ^ a b c d "A description of the x64-based versions of Windows Server 2003 and of Windows XP Professional x64 Edition". Microsoft Support Center. Microsoft Corporation. Retrieved 14 October 2011. 
  40. ^ a b "Windows NT 3.5x Setup Troubleshooting Guide (MSKB 139733)". 2006-11-01. Retrieved 2010-11-24. 
  41. ^ "INFO:Windows NT 4.0 Setup Troubleshooting Guide". 2006-10-31. Retrieved 2010-11-24. 
  42. ^ a b "System requirements for Microsoft Windows 2000 operating systems". 2007-11-13. Retrieved 2010-11-24. 
  43. ^ "System requirements for Microsoft Windows XP operating systems". 2007-09-14. Retrieved 2010-11-24. 
  44. ^ "System requirements for Microsoft Windows Vista". 2007-11-13. Retrieved 2010-11-24. 
  45. ^ "Windows 7 system requirements". Microsoft. Retrieved 2009-08-30. 
  46. ^ "Windows XP Professional System Requirements". Retrieved 7 March 2010. 
  47. ^ "Windows 7 System Requirements". Retrieved 27 January 2011. 

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