Windows Build Version Interpretation Explanation and Definition

When reading Windows related articles on My Digital Life, especially when dealing with new releases been published by Microsoft, be it at alpha, pre-beta, beta, release candidate (RC), release-to-manufacturing (RTM) or another other stage of development, there tends to be a build version number that been tagged with the code bits or the ISO images. For example, Windows 7 Beta 1 has the build number of 6.1.7000.0.081212-1400. Here’s some technical knowledge on what’s the meaning of this set of digits.

As an example, 6.1.7000.0.081212-1400 can be categorized as v.w.xxxx.z.yymmdd-ttnn.

• 6 (v) = Major Windows NT operating system (OS) version number. Currently, Windows Vista and Windows Server 2008 kernel is NT version 6. Windows 7 likely to have version 6 as major version too, as it’s built on Windows Vista kernel.
• 1 (w) = Minor version number.
• 7000 (xxxx) = Major build number.
• 0 (z) = Minor build number, which may be omitted.
• 081212 (yymmdd) = Build date stamp in the format of year, month and day).
• 1400 (ttnn) = Built time stamp in 24-hour format.

On some part of Windows operating system such as registry key BuildLab and BuildLabEx in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion, some Windows users may find a more complete build version number with build lab information. For example, Windows Vista SP1 and Windows Server 2008 has the full complete build version number of 6.0.6001.18000 (longhorn_rtm.080118-1840) and Windows XP SP2 has version 5.1 (Build 2600.xpsp_sp2_rtm.040803-2158).

In the long build tag version number, the winmain, longhorn_rtm and winmain_win7m3 are all the name of the build lab. What is build lab? Actually, there is many development teams that contribute to the final product of Windows. For example, some known teams are vbl, nt, Main or WinMain, idx01, idx02, idx03, idx05, idx06, Lab01, Lab02, Lab03, Lab04, Lab06, Lab07, Lab08, Lab09 and Lab10. Each team has area to specialize in, such as user interface, NT kernel and etc, and each team has their own view of the source tree, their own mini build lab, and builds an entire installable build. Thus, naturally, the name of the build lab is also part of the complete build tag.

For Windows 7 Beta 1 Build 7000, the build version tag is 6.1.7000.0 (winmain_win7beta.081212-1400). WinMain is the name of the team, but Win7Beta is actually component part, and most probably comes from WinMain build lab too, and not another team of WinMain_Win7Beta. Component name is completely random, some been named as just beta, core_build or just core and etc.

The existence of many build labs also explain where there are builds for Windows 7 which has higher build version, but was compiled at earlier date. And, it also explains although a build has been tagged as, let’s say beta or RC release, but there are other builds that still make the round in the news as possible leaks, such as in the case of Windows 7 build 7004.