Build lab

A build lab is a machine which produces official builds of Windows NT. Initially, there was a single build lab for the entire project. However, as the number of developers grew, teams working on different parts of the operating system were assigned their own virtual build labs, which included a branch of the project code, as well as the infrastructure to build the code. This carried over to Source Depot branch names, which led to the term being also used for the teams themselves and the branches.

Builds that were not built by a build lab are called private builds. They are identified by having the  file flag set in the executable's version information and by including the account name of the person or service who initiated the build in the branch part of the build tag.

Whistler and pre-reset Longhorn
The top-most branch was called main, which integrated changes from all labs. Under it were several numbered labs, each of which was working on a separate part of Windows, such as: These labs also had a "_N" branch, which served as a buffer between main and the actual branch. For example, changes from main would first get merged into Lab06_N before later being merged into Lab06 and vice versa.
 * Lab01: Kernel
 * Lab02: Networking
 * Lab03: Server
 * Lab04: Terminal Services
 * Lab06: User interface
 * Lab07: Internet Information Services/COM+ (added in Longhorn )

There were also idx (internal development X) labs; builds in this lab are usually recompilations intended for TAP/OEM partners. However, they were also occasionally released for public testing (e.g.: Longhorn build 4074 or Whistler build 2257).