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. 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 emulator that NT was developed under. However, they no longer carry any specific meaning.
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Features
A main design goal of NT was hardware and software portability. 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 version 4. Broad software compatibility was achieved with support for several API "personalities", including Win32, POSIX and OS/2 APIs - the latter was 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 from the BSD Unix stack).

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, gaining speed at the expense of security,[9] but this option is no longer present since Windows Vista.