The Windows Vista Epic

A Bit of History

If, like me, you're interested in all topics around computing and electronics, you must be fascinated by the Windows Longhorn saga (which became Vista).

It must be said that the history of one of the most hated operating systems in the world is full of twists and turns. Indeed, Longhorn development began in May 2001, even before Windows XP was released. Microsoft's original ambitions for this software were clear: a minor version of the system made to wait for the release of Windows 7 (then called Windows Blackcomb). However, as development progressed, many features intended for Blackcomb were added to Longhorn. This led to the reset of development on more stable foundations (.NET Server 2003 SP1) in August 2004, and Vista's release in November 2006.

Let's go back a bit to the pre-reset development phase since it's by far the most interesting.

At Microsoft (and this is the case elsewhere too), software development is divided into milestones. Longhorn had 7 before being reset. Additionally, the system is the last whose development was distributed across virtual development labs (VDL) with the following roles:

  • Lab01: Base (kernel)
  • Lab02: Network
  • Lab03: Server
  • Lab04: Management
  • Lab05: Main
  • Lab06: Desktop (user interface)
  • Lab07: IIS (Internet Information Service) / COM+ (web site graphical manager)

These labs were completely independent from each other, hence the notable differences between two versions (builds) having the same numbers but different labs.

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For example, builds 4042.main (left) and 4042.Lab06 (right) have the same version number but don't look alike. (It happens that one belongs to milestone 6 and the other to milestone 7, making it a transitional version)

As mentioned earlier, Longhorn was intended to be a "minor update to Windows XP," so its first builds looked very much like XP with a different theme superimposed over "Luna." This is the case with the first build to leak, 3683.Lab06. It features three major novelties compared to XP: the sidebar, virtual desktops (which would finally be implemented in Windows 10), and the "plex" theme (which was temporary).

Build 3683.Lab06 is also the first to identify as "Longhorn XP Professional" instead of Windows XP Professional

You may have noticed this version's wallpaper saying "Longhorn M3," meaning milestone 3. It turns out that no earlier build has leaked so far (as of July 4, 2025).

I propose to study the major builds of each milestone, as well as the features they bring:

Milestone 3 was marked by a complete visual overhaul of Windows. Indeed, it's the first to integrate a theme different from "Luna" (Windows XP's default theme), called "Plex," intended to be replaced by "Aero" later in development. The first functional versions of DCE (the rendering engine for Windows Vista's window transparency) also make their appearance in these builds. Build 3718.Lab06_N, once graphics drivers are installed, features effects during window minimization and closing, as well as partial transparency of windows.

Image from, like most, betawiki.net (link at end of article)

Milestone 4 was marked by the complete rebranding of the system, no longer referencing Windows XP. Build 4011.main (the last of the milestone) was the first to no longer feature Windows XP logos, and brought DCE functionality for window transparency that had been buggy since the beginning of the milestone. The Avalon user interface (based on .NET framework) is now usable with the new taskbar.

Build 4011.main wasn't the first to support DCE, but the builds from its milestone that preceded it had a buggy version of the rendering engine

Milestone 5 was marked by the appearance of a functional but still buggy version of WinFS (a storage subsystem based on SQL Server technology), automatic data entry (the "build string," version number in Pig Latin: onghornLay rofessionalPay), a new security screen when pressing ctrl-alt-delete, as well as a "home" edition complementary to the "professional" version.

Image 1 Image 2

Milestone 6, despite its large number of builds compared to previous milestones, didn't receive many modifications. It was marked by the addition of a new "aero" theme using the DCE rendering engine for "crystalline" transparency of window borders, the "carousel" view, and IA-64 (Intel Itanium) compatibility.

Finally, milestone 7, the longest, was marked by the replacement of the "Plex" theme with "Slate" and "jade" themes. It's the most popular milestone, as many Longhorn "reboot" projects use build 4074.idx02 as their base. It's also the last milestone before development restart, which means that all features still in "test" are found in most of its builds (aero transparency, avalon applications, buddy matchmaker, new dialog boxes, new driver installation method, ...).

Image 1 Image 2

On the right, Longhorn's default "aero" theme (after a slight modification to activate it) and on the left a modified version for the Windows Longhorn The Way It Was Meant To Be (TWIWMTB) version

The features to be attributed to Longhorn were rather vague, so much so that developers soon no longer knew which ones were intended for Longhorn or Blackcomb, and began integrating them all into Longhorn. This caused strong instabilities, particularly on builds 407x, 408x, 409x whose Windows Explorer frequently crashed or leaked memory, making them almost unusable without patches (TWIWMTB or Longhorn Reloaded for build 4074).

Facing increasingly important stability problems, as well as delays due to the inefficiency of task distribution across seven labs, Longhorn's development was reset on August 20, 2004, based on Windows Server 2003 SP1 (.NET Server 2003 SP1) source code. The last "pre-reset" build to leak is 4093.main, very unstable, which groups all of Longhorn's novelties, even those in beta or only half-working.

Build 4093.main is the last "pre-reset" build and brings novelties such as a Windows activation client prototype or "Avalon" applications based on XAML code (very unstable and non-functional Windows Movie Maker prototype)

Longhorn Project Reboots

Longhorn's adventure didn't stop on August 20, 2004. It has been continuing well beyond since many internet users continued, independently of Microsoft's will, Longhorn's development from build 4074. The interest was to make the version more stable and unlock its many hidden and/or buggy features.

Among these reboots, the best known are Longhorn TWIWMTB, Longhorn Reloaded, and SigmaOS.

Patches for the vanilla Longhorn 4074 version also exist, the best known being Longhorn 2008 Beta 2.

For More Information

In this section, the different sources of this article are listed, as well as other resources to learn more.

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