Windows NT 4.0
|Microsoft Windows NT 4.0|
|Shell Update Release|
|CPU architecture||x86, MIPS R4000, DEC Alpha, PowerPC|
|Preceded by||Windows NT 3.5x|
|Succeeded by||Windows 2000|
Microsoft Windows NT 4.0 (codenamed Shell Update Release) is the successor to Windows NT 3.51 and the first version of Windows NT to feature the Windows Explorer interface introduced in Windows 95. It is the last version of Windows NT to include NT in its product name.
There are two editions of Windows NT 4.0. It has been found out that the only difference between the two editions (Server and Workstation) lied only in the Registry and the missing Server files.
Windows NT 4.0 Workstation was designed for general desktop use.
Windows NT 4.0 Server (Server, Server Enterprise Edition, Terminal Server) were designed to serve web pages to multiple clients using IIS.
There were 6 service packs released for Windows NT 4.
Service Pack 7
There was a 7th Service Pack planned, but it was canceled and Security Update Rollup 6a was released instead. 
In a support document titled "Update on Windows NT 4.0 Service Pack 7", Microsoft stated that:
Windows NT 4.0 Service Pack 6a, the most recent service pack for Windows NT, was released in November of 1999. Since then, Microsoft has been supporting our customers with a series of hotfixes in response to specific concerns, including security vulnerabilities. Microsoft intends to continue supporting customers by making hotfixes available as they are needed. However, since the release of Service Pack 6a, the frequency of critical problems reported to Microsoft has declined significantly. Microsoft originally planned on releasing Service Pack 7 late last year, approximately 1 year after the release of SP6a. At the time, Microsoft had produced relatively few post-SP6a hotfixes, and decided to delay SP7 until Q3 of 2001. The frequency of hotfixes has continued to decline, and now, well over 1 year beyond the last SP, we still have made fewer fixes than were included with either SP5 or SP6.
We discussed with a number of our customers their use of recent service packs, and their requirements for an additional service pack. From these discussions we learned that most customers are running a combination of Service Pack 5 and Service Pack 6; in some cases with 3-5 additional hotfixes. These customers told us that these service packs, particularly Service Pack 6a, have been very stable. There were three reasons we heard that customers were anticipating Service Pack 7:
- An easy mechanism for deploying the security fixes Microsoft has publicly released since SP6a.
- Availability of the Windows NT 4.0 Active Directory client, originally planned to be part of SP7—now available for download at http://www.microsoft.com/windows2000/news/bulletins/adextension.asp.
- International versions of the Internet Explorer High Encryption Pack for Windows NT are available and downloadable at: http://www.microsoft.com/windows/ie/.
Based on discussions with our customers, we have come to the conclusion that Service Pack 7 is not needed, but that an easy way to deploy our publicly released security fixes would be appreciated by many of our customers. It is clear to us that our customers would rather have a smaller, lightweight, easily deployable way to secure their systems, rather than potentially disrupt their stable environments with another large service pack. Microsoft is therefore planning to release a comprehensive rollup of all Windows NT 4.0 security vulnerabilities as a single package in Q3 2001.
Microsoft recognizes that some companies have been planning on a new service pack, especially since Microsoft had previously given indications that Service Pack 7 would be released. For customers who were planning on deploying Service Pack 7, we now encourage them to focus on completing rollouts of Service Pack 6a, in combination with the planned security pack. Microsoft will provide detailed instructions for deploying Service Pack 6a with the security pack.
While Microsoft will not offer any further service packs for NT 4.0, we are committed to providing regular service packs for the currently released operating system, Windows 2000. Service Pack 2 for Windows 2000 will be released in the near future. As new versions of Microsoft operating systems are released, Microsoft will continue to evaluate the need for service packs based on our customer's requirements and feedback, and the stability of the operating system.
— Microsoft, 
- Windows NT 4.0 Build 1124.1
- Windows NT 4.0 Build 1130.1
- Windows NT 4.0 Build 1141.1
- Windows NT 4.0 Build 1166.1
- Windows NT 4.0 Build 1175.1
- Windows NT 4.0 Build 1198.1
- Windows NT 4.0 Build 1201.1
- Windows NT 4.0 Build 1209.1
- Windows NT 4.0 Build 1227.1
- Windows NT 4.0 Build 1234.1
- Windows NT 4.0 Build 1264.1
- Windows NT 4.0 Build 1273.1
- Windows NT 4.0 Build 1287.1
- Windows NT 4.0 Build 1293.1
Release Candidate 1
Release Candidate 2
There was also an unidentified Workstation RC2 build, mentioned in Fate 103 warez CD.
Service Pack 1
Service Pack 2
Service Pack 3
Service Pack 4
Service Pack 5
Service Pack 6
Service Pack 6a
Post-Service Pack 6a Security Rollup
Source code leak
For detailed information, see the main article: Windows source code
In 2004, a large portion (approximately 80-95%) of the Windows NT 4.0 (with Service Pack 3) source code was leaked. Further investigations by Microsoft found that the source was leaked from Mainsoft, a software porting company (which ported Internet Explorer to Unix before such edition was dropped).
In 2010, the source was successfully compiled producing about 318MB of binaries.