Windows NT

Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was originally designed to be a powerful high level language based processor independent multiprocessing multiuser operating system with features comparable to UNIX to complement workstation versions of Windows that were based on MS-DOS until 2001. It was the first 32-bit version of Windows. Since increases in processor performance, Windows XP and Windows Server 2003 are actually the latest versions of Windows NT, though they are not branded as such for marketing purposes.

Major Features
The original version of Windows is a 16-bit GUI program which runs on MS-DOS and was written in Intel 8086 assembler. MS-DOS uses interrupts to call operating system services. 16-bit Windows is characterised by the use of 16-bit near pointers, 32-bit far pointers, and an awkward memory allocation system which requires the programmer to lock down a pointer to obtain a physical address and then release it so the operating system can relocate objects as needed to maximise efficiency. This was made necessary by the segment-based addressing of the Intel 8086 based processor which essentially adds a 4-bit extension to the 16-bit addressing of the Intel 8080. DOS was also written to suit the needs of a single user, with minimal security. A user with Windows 95 who does not type in a proper password still can access the local resources, if not the network. 16-bit Windows is also built around the concept of cooperative multitasking. A program must do operations quickly and then give control back to Windows, which can then give messages to other tasks. If a program fails to do so, it will stop all other processes on the machine, rendering it inoperable, and this often happened on Win16 machines.

Microsoft had marketed XENIX as a version of UNIX, but it never became very popular as a business operating system. The Intel 8086 was not a very powerful processor, but the 286 and 386 had features which could support an true multitasking environment. Win32 replaces the earlier memory allocation scheme with true 32-bit pointers, permitting a 4 gigabyte address space (with 2 gigabytes for application code) exceeded on actual machines only by the 2000s. Operating system calls are made with conventional subroutine calls, and a sophisticated system manages users and privileges to meet corporate and defence standards. If the administrator loses the login password, the system must be rebuilt.

Windows NT supports preemptive multitasking and threading like most large scale systems. The kernel can stop any task and start others without help from the application programmer. NT also manages virtual memory like a time sharing computer and supports networking and remote terminals. NT is generally not compatible with UNIX in terms of programming APIs except in areas such as Windows Sockets which are patterned after Berkeley Sockets, but otherwise NT tends to be comparable in features and capabilities. The NTFS file system has powerful multiuser and security features, with long file names and large disk addressing capability compared with the DOS-based FAT system. Many SQL Server and IIS features require the use of NTFS.

Market Share
NT has grown from being called "Nice Try" to passing Unix in 2005 for sales of servers according to IDC, a market research firm based in Framingham, Mass. Others observe that Windows NT servers using IIS, ASP and ASP.NET by the 2000s had a diminishing share of web and corporate servers (under 30%) with UNIX dominating with over 70% of the market. The entry level $99 workstation Windows XP lacks the ability to run SQL Server databases and IIS web servers and other corporate features found in Professional and Server versions, but NT is now a major platform for PC based games. Since NT has become the base technology for workstations, it nearly completely dominates desktop and laptop workstations with Apple a distant second and Linux yet fewer.

Development
When development started in November 1988, Windows NT (using protected mode) was to be known as OS/2 3.0, the third version of the operating system developed jointly by Microsoft and IBM. In addition to working on three versions of OS/2, Microsoft continued parallel development of the DOS-based and less resource-demanding Windows environment (using real mode). When Windows 3.0 was released in May 1990, it was 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 be as immediately popular as Microsoft's 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.

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 has led some writers to refer to the kernel as a microkernel, but the Windows NT kernel no longer meets many of the criteria of a 'microkernel', although this was the original goal of chief architect Cutler. 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; it was this that allowed the late adoption of the Windows API (into the Win32 subsystem). Windows NT was the first operating system to use Unicode internally.

Releases
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. The NT version is no longer marketed, but is said to reflect the degree of changes to the core of the operating system. The build number is an internal figure used by Microsoft's developers.

Supported platforms
Like Unix, NT was written in a high level language such as C. It can be recompiled to run on other processor systems, at the expense of larger and slower code. For this reason, NT was not favored initially for use with slower processors with less memory. It also 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, nearly all actual NT deployments have been on x86 architecture processors.

Windows NT 3.1 ran on Intel IA-32 x86, DEC Alpha, and MIPS R4000 processors. Windows NT 3.51 added support for PowerPC processors. Intergraph Corporation ported Windows NT to its Clipper architecture and later SPARC, but neither version was sold to the public. Windows NT 4.0 was the last major release to support Alpha, MIPS, or PowerPC, though development of Windows 2000 for Alpha continued until 1999, when Compaq stopped support for Windows NT on that architecture. 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 3rd parties (Motorola, Intergraph, etc.) have few, if any, publicly available updates.

Windows XP 64-Bit, Windows Server 2003 Enterprise, and Windows Server 2003 Datacenter support Intel's IA-64 processors. As of April 25 2005 Microsoft had released four editions for 'x64' (AMD64 or EM64T): Windows XP Professional x64 Edition, Windows Server 2003 Standard x64 Edition, Windows Server 2003 Enterprise x64 Edition, and Windows Server 2003 Datacenter x64 Edition.

The Xbox uses a heavily modified and stripped down Windows 2000 kernel. This kernel was heavily modified again for the Xbox 360 which runs on PowerPC. This version is not for separate sale, and little is known about it.

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 current Draft Revision 0.8 (March 10 2006) requires 512 MB of main memory for 6.0, an 8-fold increase on the previous release. No specifications for processors or free disk space have been published for Vista at the time of writing.

'NT' designation
It is popularly believed that Dave Cutler intended the initialism 'WNT' as a pun on VMS, incrementing each letter by one, similar to the apocryphal story of Arthur C. Clarke deriving HAL 9000's name by decrementing each letter of IBM. While this would have suited Cutler's sense of humor, the project's earlier name of NT OS/2 belies this theory. Another of the original OS/2 3.0 developers, Mark Lucovsky, states that the name was taken from the Intel i860 processor&mdash;code-named 'N-Ten'&mdash;which served as the original target hardware. 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.

The letters were dropped from the name of Windows 2000, though the box contained the phrase 'Built on NT technology'. This action ostensibly reflected Microsoft's intent to unify its home and business lines, then represented by Windows 98 and Windows NT 4.0, but this goal would not be achieved until the introduction of Windows XP. Some believe this to be the result of a trademark dispute between Microsoft and Nortel as on the bottom of the Windows NT 4.0 product boxes is a notice explaining that 'NT' is a trademark of Northern Telecom.