Windows NT (Or "New Technology") is Microsoft's business-class operating system, or OS. It is based on a semi-microkernel design. Microsoft's microkernel is called the HAL or hardware abstraction layer and handles only access to hardware, where other microkernels also handle memory allocation and process control. Windows' great success is predicated on the fact that the Win32 API set is an extension of the API used by Windows 3.1, which meant that original 16 bit windows applications could mostly be used on NT and take advantage of its improved memory model with nothing more than a recompile; It is also popular largely because workstation and server run the same operating system, thus simplifying administration and lowering TCO, or total cost of ownership as compared to a heterogenous environment. NT's core logic was written by a number of ex-DEC engineers, which gives rise to a variety of rumors about its similarity to VMS -- some of which are true. Windows NT also features a number of other significant advantages over Windows 95 (and its descendants) including a partially journaling file system known as NTFS which also provides security in a way that FAT16 and FAT32 filesystems cannot; it provides ACLs (access control lists) and a broad, extensible permissions scheme which can be used to allocate a wide number of fairly atomic rights.

The name "NT" did not originally mean "New Technology". It stood for "N-Ten", an early simulator of the Intel i860, the CPU at which Windows NT was originally targeted. The i860 had not yet seen silicon and only the emulator existed; it was named "NT" because it ran on the N-Ten. Interestingly, the next CPU targeted by Windows NT (after abandonment of the i860 architecture) was the MIPS R3000, but we know it best for its support of the intel i386 because of its wide distribution.

Windows NT actually grew (in a way) out of OS/2 version 2. OS/2 was a collaboration between Microsoft and industry giant IBM, who had been delivering DOS on their PC computers essentially since their inception. Microsoft detached themselves from OS/2 in between versions 2 and 3; Both IBM and Microsoft retained the rights to whatever they had taken away with them. This allowed OS/2 2.1 to come out with a DOS compatibility layer which would actually be able to run Windows 3.1 within it, but it was too little too late. Rather than continue to work with IBM, Microsoft decided to implement the Windows 3.0 API and a workalike 32-bit implementation thereof, and release their own operating system. Windows NT did retain an OS/2 compatibility layer, and the OS/2 HPFS "high performance file system".

Windows NT has come in a variety of different versions and flavors over time. The original was Windows NT 3.1, which mimicked Windows 3.1, though it was on an entirely different level since it was a 32 bit rather than 16 bit operating system. Released on July 27, 1993, NT 3.1 made use of the MMU provided in the i386 architecture, delivering protected and virtual memory at a level seamless to applications. It was followed on September 21, 1994 by Windows NT 3.5 (Code-named "Daytona") which delivered significant performance improvements and a Netware client. The Netware client really enabled Microsoft to move into the market because most file servers at the time were running Novell. On May 30, 1995, 3.5 was replaced by Windows NT 3.51, a version whose primary purpose was to deliver PowerPC support. IBM was nine months late delivering PowerPC and so Microsoft took this time to do a number of bug fixes, making 3.51 the most stable release of Windows at the time. Depending on who you talk to, you may be told that it is still the most stable version of windows.

3.51 was superseded on July 31, 1996 by Windows NT 4.0 ("Cairo") which included the Windows 95 ("Chicago") user interface. Unfortunately, Microsoft moved large portions of the user interface into the kernel's memory space. This meant it was possible for the user interface to access and overwrite portions of memory which do not strictly belong to it, and reliability suffered dramatically. NT 4.0 also included Microsoft's first attempts to implement Plug and Play on Windows NT for ISA expansion cards, which largely went badly awry. Windows NT 4.0 is also known as the "Shell Update Release" because the largest single change is that from the Windows 3.1 style interface (File Manager and Program Manager) to the Windows 95 style interface (featuring a Start Menu and integrating file and program management into a single program.) NT 4.0 also provided support for the DEC Alpha processor, a true 64 bit architecture which was at the time the fastest individual processor available and which powered systems running VMS and Unix. This was made possible primarily because NT was designed for portability from the beginning. Unfortunately, NT 4.0 (service pack 3) is the last version of NT to have support for PowerPC or Alpha.

NT4 was finally replaced by Windows 2000 on February 17, 2000; Note the dropping of the "NT" designation, though the start screen will happily inform you that it is based on "NT Technology", a redundant statement similar to "NIC card" or "ATM machine". Windows 2000's version number indicates that it is Windows NT 5.0. Windows 2000 brought a number of significant advantages, including proper support for Plug and Play, USB, IEEE 1394/Firewire, and other technologies. Windows' "Domain" system for user authentication was replaced at this time with a system based on LDAP and Kerberos with data provided via DNS, called Active Directory. AD is largely internet-centric, and uses domain names to replace the original Windows NT Domains.

October 25, 2001 brought us Windows XP ("Whistler"), aka Windows NT 5.1. XP provided a new, skinnable interface which is nonetheless still based on the interface brought over on NT 4 from Windows 95. It also provided a more user-friendly interface for logging in and handling security and file sharing, and a number of Wizards to handle common tasks. Windows XP also provides support for uPnP or Universal Plug and Play, a system for the autoconfiguration of network devices, largely championed by intel. Even the home edition features the ability to control the system remotely through what is now called "Remote Desktop Connection" but has previously been known as "Terminal Services" (In Windows 2000.) Windows XP is about to be released in a 64 bit version for the AMD x86-64 processors (Hammer core) which will also work with the AMD-compatible intel EMT64-extended processors.

Windows 2000 was superseded by Windows Server 2003 on April 24, 2003. This version of Windows has significantly more separation between processes than earlier versions, and as such is somewhat slower but has better security. In particular most items default off to decrease potential points of failure. For example, IIS installs without any dynamic content. Server 2003 is also going to support x86-64, and already supports Intel's Itanium processors, 64 bit VLIW-architecture units in little demand.

NT 6.0, or "Windows Vista" was released to businesses November 30, 2006, and to the general public January 30, 2007. It has so far (May 10, 2008) been, to say the least, a boondoggle; it is slower than Windows XP at nearly all operations and has proved to be perhaps the least backwards-compatible version of Windows ever (with the possible exception of the Windows 98-derived Windows ME.) While Vista incorporates numerous feature improvements and fairly dramatic upgrades to its GUI, the end result (Even through the use of new technologies intended to make the system faster, some of which Vista was the first operating system to support) is less efficient and responsive than its predecessor.

The server edition of NT 6, "Windows Server 2008", was released February 27, 2008. Unlike former editions of Windows NT Server which largely differ from the Workstation Edition (and since Windows XP, the Home Edition as well) only in the included management tools and in some registry settings which control the number of connections allowed, this version includes numerous pieces of functionality not found in the cheaper versions including a GUI-less install, Windows Powershell, Self-Healing NTFS, a Hypervisor-based Virtual Machine (aka Virtualization) package called Hyper-V, and detailed process resource management.

Today, Windows NT is one of the leading server and desktop operating systems. Widely deployed both in the home (mostly in the form of Windows XP) and on servers, it provides a single, seamless interface between desktop and server, meaning that the same applications will run on both, and minimizing the amount of training necessary to support a single enterprise. Similar to other operating systems such as Linux or the various BSD variants, it comes with everything you need to get up and start doing useful work from the beginning; a web server, ftp server, tools for administration, and so on. It is considered to be less stable than most Unix variants and certainly comes packaged with less software, but is nonetheless the leading operating system in the world today due to various issues such as having a uniform interface across platforms, strong (though often expensive) support, and essentially having gotten there first. Over time it has shaken off (admittedly limited) competition from IBM's OS/2 Warp and various Unixes to sit in the top spot in the commercial world in terms of low-end and small business servers. Whether you agree or disagree with NT from a technical or even moral standpoint, one must accept that there is a high amount of momentum behind the platform.

As of May 10, 2008, the most recent release version of Windows NT server is Windows Server 2008. The latest release version of Windows NT for home is Windows Vista.


  1. Thurrott, Paul. Windows Server 2003: The Road To Gold Part One: The Early Years., January 24, 2003. (
  2. "Windows NT." Wikipedia, The Free Encyclopedia. 7 May 2008, 02:22 UTC. Wikimedia Foundation, Inc. 10 May 2008 <>.
  3. "Windows Server 2008." Wikipedia, The Free Encyclopedia. 10 May 2008, 05:14 UTC. Wikimedia Foundation, Inc. 10 May 2008 <>.