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. 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 based on Windows NT, although they are not branded as Windows NT.
Although various Microsoft publications, including a 1998
question-and-answer session with Bill
Gates, reveal that the letters 'NT' were expanded to 'New
for marketing purposes, they originally stood for 'N-Ten', the codename
i860 processor that NT was initially developed for.
However, they no longer carry any specific meaning.<br>
Microsoft decided to create a portable operating system, compatible
and POSIX support and with multiprocessing in October 1988.
When development started in November 1989, Windows NT was to be known
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. When Windows 3.0 was released in May 1990, it 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 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