Windows NT 3.1, 3.5, 3.51, 4.0

NT 3.1
Windows NT 3.1 is an operating system that was produced by Microsoft as part of the Windows NT family of operating systems. It was released on July 27, 1993.

At the time of Windows NT's release, Microsoft's Windows 3.1 desktop environment had established brand recognition and market share; but Windows 3.1 relied on the DOS operating system for essential functions, and it had a constrictive 16-bit architecture. Windows NT, however, was a complete, 32-bit operating system that retained a desktop environment familiar to Windows 3.1 users.

By extending the Windows brand and beginning Windows NT at version 3.1, Microsoft implied that consumers should expect a familiar user experience. The name Windows NT ("New Technology") advertised that this was a re-engineered version of Windows.

Windows NT began as a rewrite of the OS/2 operating system, which Microsoft had co-developed with IBM in the 1980s. For several reasons, including the market success of Windows 3.0 in 1990, Microsoft decided to advance Windows rather than OS/2. They relinquished their OS/2 development responsibilities to IBM, and forked their work on OS/2 v3.0 into a competing operating system.

Windows NT 3.1 was available in two editions: Windows NT 3.1 for workstations, and Windows NT 3.1 Advanced Server for servers. When these premiered, their sales were limited by high system requirements, and a general lack of 32-bit applications to take advantage of the OS's data processing capabilities.

NT 3.5
Windows NT 3.5 is an operating system developed by Microsoft, released on September 21, 1994. It is the second release of Windows NT.

One of the primary goals during Windows NT 3.5 development was to improve the operating system's performance. As a result, the project was codenamed "Daytona", after the Daytona International Speedway in Daytona Beach, Florida. Like many other older Windows versions before 1996, Microsoft stopped supporting Windows NT 3.5 on December 31, 2001. Support for Windows NT 3.51 Workstation also ended in that date.

Features
Windows NT 3.5 comes in two editions: NT Workstation and NT Server. They respectively replace the NT and NT Advanced Server editions of Windows NT 3.1. The Workstation edition allows only 10 concurrent clients to access the file server and does not support Mac clients.

Windows NT 3.5 includes integrated Winsock and TCP/IP support. (Its predecessor, Windows NT 3.1, only includes an incomplete implementation of TCP/IP based on the AT&T UNIX System V "STREAMS" API.) TCP/IP and IPX/SPX stacks in Windows NT 3.5 are rewritten. NetBIOS over TCP/IP (NetBT) support as a compatibility layer for TCP/IP was introduced as also the Microsoft DHCP and WINS clients and DHCP and WINS servers.

Windows NT 3.5 can share files via the File Transfer Protocol, and printers through the Line Printer Daemon protocol. It can act as a Gopher, HTTP, or WAIS server, and includes Remote Access Service for remote dial-up modem access to LAN services using either SLIP or PPP protocols. Windows NT 3.5 Resource Kit includes the first implementation of Microsoft DNS.

Other new features in Windows NT 3.5 include long filenames of up to 255 characters, Object Linking and Embedding (OLE) version 2.0 and support for input/output completion ports. Microsoft updated the graphical user interface to be consistent with that of Windows for Workgroups 3.11. NT 3.5 shows performance improvements over NT 3.1, and requires less memory.

NT 3.51
Windows NT 3.51 is the third release of Microsoft's Windows NT line of operating systems. It was released on May 30, 1995, nine months after the release of Windows NT 3.5, and three months before the release of Windows 95. The release provided two notable feature improvements; firstly NT 3.51 was the first of a short-lived outing of Microsoft Windows on the PowerPC architecture. The second most significant enhancement offered through the release was that it provides client/server support for inter-operating with Windows 95, which was released three months after NT 3.51. Windows NT 4.0 became its successor a year later. Support for NT 3.51 ended in 2001 and 2002 for the Workstation and Server editions, respectively.

Overview
The release of Windows NT 3.51 was dubbed "the PowerPC release" at Microsoft. The original intention was to release a PowerPC edition of NT 3.5, but according to Microsoft's David Thompson, "we basically sat around for 9 months fixing bugs while we waited for IBM to finish the Power PC hardware". Editions of NT 3.51 were also released for the x86, MIPS, and Alpha architectures.

New features introduced in Windows NT 3.51 include PCMCIA support, NTFS file compression, replaceable WinLogon (GINA), 3D support in OpenGL, persistent IP routes when using TCP/IP, automatic display of textual descriptions when the mouse pointer was placed on toolbar buttons ("tooltips") and support for Windows 95 common controls.

In view of the significant difference in the kernel base, Windows NT 3.51 is readily able to run a large number of Win32 applications designed for Windows 95. More recent 32-bit applications will not work, as the developers have prevented their application from working with any Windows version earlier than Windows 98, and also because some applications do not work properly with the older Windows NT 3.51 interface.

Despite this, Microsoft in their application releases muddied the issue, releasing 32-bit versions of Microsoft Office right up to Office 97 (the last version of Microsoft Office supported on NT 3.51), but relying upon 16-bit versions of Internet Explorer technology from versions 3.0 to 5.0. Web browsers based on and including Firefox were operable up to version 2.0.0.22, released in April 2009; they required a few manual file updates to work without compromising browsing security.

Windows NT 3.51 is the last of the series to be compatible with the Intel 80386 processor.

NewShell
On May 26, 1995, Microsoft released a test version of a shell refresh, named the Shell Technology Preview, and often referred to informally as "NewShell". This was the first incarnation of the modern Windows GUI with the Taskbar and Start menu. It was designed to replace the Windows 3.x Program Manager/File Manager based shell with Windows Explorer-based graphical user interface. The release provided capabilities quite similar to that of the Windows "Chicago" (codename for Windows 95) shell during its late beta phases; however, it was intended to be nothing more than a test release. There was a second public release of the Shell Technology Preview, called Shell Technology Preview Update made available to MSDN and CompuServe users on August 8, 1995. Both releases held Windows Explorer builds of 3.51.1053.1. The preview program provided early feedback for the Shell Update Release, the next major Windows NT version with the new interface built-in, which was released in July 1996 as Windows NT 4.0.

Updates
Five Service Packs were released for NT 3.51, which introduced both bug fixes and new features. Service Pack 5, for example, fixed issues related to the Year 2000 problem.

NT 4.0
See Windows NT 4.0.