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 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 Technology' for marketing purposes, they originally stood for "N-Ten," the codename of the Intel i860 XR processor for which NT was initially developed. However, they no longer carry any specific meaning.
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, and AMD64 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, and OS/2 APIs - the latter two were phased out starting with Windows XP. Partial MS-DOS compatibility was achieved via an integrated DOS Virtual Machine - although this feature is being phased out in the x86-64 architecture. 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.)
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