Windows Longhorn build 4015 (main)

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Build of Windows Longhorn
OS family
Timebomb2004-03-25 (+363 days)
Works in
2018-01-07 172901.png
Preinstallation Environment
TCB.png TCBGallery.png

Windows "Longhorn" build 4015, with a build tag of 4015.main.030328-1500 is a "Longhorn" Milestone 5 build. This is the first Milestone 5 build, leaked on 2003-04-28 by WiNBETA.

Please note: that there is a second build numbered 4015. This was compiled by build lab06 rather than main, and information on it is scarce.

New features and changes

  • The wallpaper has changed to a Milestone 5 background, being slightly darker than the Milestone 4 background and containing the Windows logo instead of the Longhorn logo.
  • The latter year in the Longhorn branding in "winver" and About Program dialogs has been changed back to 2003.
  • A new login screen is utilized, replacing the Windows XP login screen.
  • Windows Explorer has been written in .NET managed code, although this often causes memory leaks and frequent crashes.[1]
  • Parental controls
  • The Windows Sidebar now gives a separate taskbar when enabled, which overrides the current theme the taskbar has.
    • Additional configurability for the sidebar - including being able to put it below the start bar at the bottom of the screen
  • "Libraries" - later introduced in Windows 7
  • Download manager - which was eventually dropped
  • WinFS - causes memory leaks
  • Push notifications - later introduced in Windows 8
  • Desktop Composition Engine - can be enabled with the uxdesk.dll,DceStart command in the Run dialog box. Note that a DX8 graphics card is required or DCE will crash. Only window transparency included.



Most copies of this build's CD are not bootable due to corruption, since it results in an "NTLDR is missing" error. If booting from the installation media only results in an "NTLDR is missing" error, it can only be upgraded from an earlier build.

Memory Leak

Windows Explorer has several memory leaks which can make this build difficult to use. Turning off the Sidebar will usually stop these memory leaks.