Windows Longhorn

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For post-reset history and builds, see Windows Vista.
Windows Longhorn
Windows Longhorn Logo.png
Windows "Longhorn"
Preliminary name
Kernel version NT 6.0
CPU architecture x86, x64, IA-64
Release date N/A
Support end N/A
Preceded by Windows XP
Succeeded by Windows Vista

Longhorn was the codename for the planned successor of Windows XP.

One of the original - and largest - changes is that, with "Longhorn", the .NET Framework would be integrated into the core Windows platform, deprecating the traditional Win32 API. During development, portions of the operating system were rewritten, causing memory leaks and instability, particularly in Windows Explorer.

Development was reset, but post-reset builds continued to use the "Longhorn" codename until the final name, Windows Vista, was announced on 22 July 2005.



"Longhorn" was chosen as the codename for the operating system to represent its initial status as an internim release between Windows XP (codenamed "Whistler") and "Blackcomb". Whistler and Blackcomb are names of mountains in British Columbia, Canada,[1][2] and Longhorn is the name of a saloon located in between the two mountains, representing the operating system's initial status as an internim release between the two products.[3] Bill Gates would later state that this choice for a codename of the operating system was "a bit random".[4]


The popular belief is that pre-reset "Longhorn" builds are based on Windows XP. This was likely spurred by Paul Thurrott's statement on his review of build 5048: "The problem, I was told recently, was that the underpinnings of Longhorn--then based on the Windows XP code base--were struggling under the weight of all of the technologies that Microsoft planed to implement in this release."[5] However, pre-reset "Longhorn" builds are based, not on XP, but on Windows Server 2003 release candidate code. The xpclient release branch, dedicated to XP, spun off from the main branch in 2001. The main branch continued to compile Server 2003 builds at the 3xxx range, such as build 3663 (release candidate 1), until the dnsrv branch dedicated to Server 2003 spun off from the main branch in 2002. After that, the main branch began compiling Longhorn builds.[6]


Several different logos were created throughout the development of "Longhorn". Early builds used 2D and 3D representations of a longhorn bull; later builds included white or glass versions of the Windows flag.

Concepts, presentations, demos and prototypes

Implementation of concepts

Twitter user Lucas Brooks (mswin_bat) found that porting the private Milestone 7 Aero theme to a Milestone 5 build like 4017 enables the striped sidebar shown in a demo.[8]


For server builds, see the Windows Server 2008 page.
  • No information available
  • Existence doubtful
  • Information or pictures available
  • Leaked or released

Lab guide (Source: Grabberslasher)[9]

  • Lab01: Base (Kernel)
  • Lab02: Networking
  • Lab03: Server
  • Lab04: Management
  • [Lab05:] Main
  • Lab06: Desktop
  • Lab07: IIS/COM+

Milestone 1&2

Planning stage. No builds known.

Milestone 3

Milestone 4

Milestone 5

Milestone 6

Milestone 7

Development reset

See Windows Vista.

See also


See also

BetaArchive forum

External links


Paul Thurrott

Other non-Microsoft