Starting this build introduces many bugs, ex.

Requires patching to show up in Explorer.

The only build that had Animated Preview Pane Aurora.

However, it requires some work in order to enable it.

The first build that included full DWM and Aero.

The first build that had 64-bit version.

The first build that had a checked version.

New Setup UI, screen saver and logon screen.

'Start' is removed from the Start Menu button (when sidebar is enabled) and 'My' in the Start menu is removed everywhere.

New logon screen, wallpaper and boot screen.

Plex theme is replaced by Slate (only lab06_n compile).

The first build that had ia-64 version.

Some improvements in the Internet Explorer.

The first build that had Home Edition SKU.Wallpaper and logon screen were updated.Some changes in the Setup UI and Plex theme.Ctrl+Alt+Delete now opens a security interface instead of Task Manager.Skipped OOBE and changed watermark to 'Longhorn Professional'.Windows Messenger was updated to version 5.0.Some improvements in Internet Explorer.Using install.wim during the installation.Removed Classic View from Control Panel.The only build to contain both Media Center and Tablet PC editions.Animated files and folders icon in the Explorer.A new display settings applet was introduced, based on the Windows Presentation Foundation.Internet Explorer was updated to version 6.05.First build to include Desktop Composition Engine (basic window transparency effects).After that, the main branch began compiling Longhorn builds. 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. The xpclient release branch, dedicated to XP, spun off from the main branch in 2001.

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.' However, pre-reset 'Longhorn' builds are based, not on XP, but on Windows Server 2003 release candidate code.

The popular belief is that pre-reset 'Longhorn' builds are based on Windows XP. Bill Gates would later state that this choice for a codename of the operating system was 'a bit random'. Whistler and Blackcomb are names of mountains in British Columbia, Canada, 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. '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'.

4 Concepts, presentations, demos and prototypes.

Longhorn wallpaper windows 1080