Windows Longhorn build 4015 (main)

Windows Longhorn build 4015 (main)  is one of the first Milestone 5 builds of Windows Longhorn, which was shared on 26 April 2003 by WiNBETA.

Setup
Setup has received a few minor design uplifts compared to build 4011.

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.
 * Windows Explorer has been written in .NET managed code, although this often causes memory leaks and frequent crashes.
 * Parental Controls is updated to now restrict games that are rated higher than a specfic ESRB rating.
 * This build includes Libraries. The libraries included is the Photo and Video Library, Music Library, Document Library, and Game Library; the latter doesn't work. It was later introduced in Windows 7.
 * WinFS now works, but it often causes memory leaks.
 * Notifications once again have been slightly updated.
 * The Plex theme has received a few updates, such as buttons now having animations upon hovering over them.
 * The Windows start button has changed, being different than the start button shown from builds 3683 - 4011.
 * The glass borders make their first appearance in this build, but they require patched . This variant of DCE is also included in builds 4017 and 4020.
 * There is an early version of a new Help Center included in the  folder. Opening it causes a Trust Advisor warning to pop up.

Sidebar and taskbar
The new taskbar given from the Windows Sidebar is enabled by default, and you can no longer get the old taskbar with the sidebar enabled. This new taskbar overrides any theme that is utilized. Tiles for the sidebar have also been updated slightly, such as the search tile, which has been modified to be slightly more fitting.

Login screen
A new login screen is utilized, replacing the Windows XP login screen. It also uses the wallpaper found in builds 3706 to 4001 albeit being zoomed in on the top-right by default, however it doesn't use animations found in later builds. Additionally, an ability to set custom login screen background has been added; that can be done by setting any path to image in  string value, that is located in   registry key.

Installation

 * Many drivers aren't installed by default during the hardware portion of setup and have to be installed manually.
 * On some installs, once copying files has completed, setup will fail to create a  file. Although booting will still be possible,   will default to.
 * The hardware setup tends to hang easily, after a while, you can press ⇧ Shift to open the Command Prompt, then run  and terminate the process   to log in. Due to this, the Out-of-Box Experience will not run.
 * Most copies of this build's installation media are not bootable due to corruption, since it results in an "NTLDR is missing" error. If booting from the installation media results in an "NTLDR is missing" error, it can either be upgraded from an earlier build (except build 4011 on some machines, which will give a  BSOD) or it can be fixed with a patch. The ISO image of this build found on BetaArchive's FTP server does not have this issue.
 * On some machines, booting from the CD may take longer than expected.

Login screen
Password hints have no effect on this build as the new login screen has no option to show a hint.

Memory leak
As with most later Longhorn builds, this build's Explorer tends to leak memory after a while. Turning off the Sidebar reduces the effect of the memory leak. WinFS and related services are also affected by major memory leaks. Disabling WinFS solves the problem.

Drivers
When certain Anti-virus drivers are installed, inserting or unplugging a USB device may result in a  bugcheck.