Windows Longhorn build 4051

Windows Longhorn build 4051 is a Milestone 7 build of Windows Longhorn. It is the build given to attendees of Microsoft's Professional Developers Conference 2003 in Los Angeles, California, which was held during the 27 October to 30 October of that year as a cut-down release from the demo builds shown off at that conference, making it one of the only two pre-reset Longhorn builds that received a widespread release by Microsoft, the other being build 4074.

This build comes in x86, x64 and IA-64 variants. The x64 version is not overly different from the x86 version, but it has a new setup style and several apps including Internet Explorer 6 have been optimized for x64 (often, the x86 versions do not run).

This build was compiled in evaluation mode and can be installed on the current date. Attempting to log onto the desktop once the timebomb has been triggered will return the user to the login screen.

Setup
Although the setup process overall is similar to previous builds of Longhorn, you cannot upgrade to this build from a previous build of Longhorn, due to this being a PDC build.

Explorer

 * New Documents and Photos and Videos libraries.
 * The prefix "My" was dropped in most of the remaining folders, resulting in new names for locations Computer, Network Places and Contacts.

Internet Explorer
Internet Explorer 6.05 included an add-on manager, a download manager, pop-up blocker, and a tool to quickly delete browsing history.

Other new features and changes

 * A new TCP/IP stack. IPv6 is also enabled by default in this new stack.
 * Self-Healing NTFS was added in this build.
 * The top buttons in the migration wizard now function.
 * The  banner has been changed to align with the new Slate theme.

Shell
The x64 and IA-64 compile of this build lacks the Sidebar and Explorer preview pane as a result of the absence of the Avalon framework, which was still being implemented onto different architectures at the time of compilation. It would eventually be completely ported over and included by default starting with the IA-64 compile of build 4067.

ClearType
Some copies of this build's x86 counterpart do not have ClearType font smoothing enabled by default.

Notifications
Notifications tend to reappear quite a lot, until the user reaches a certain point where they will finally close for real upon closing. To fix this, disable the Sidebar or click on Options, and then click on "Don't show this again".

TCP/IP stack
The TCP/IP stack has a few bugs, however, most of them were fixed in build 4053.

x64 build specifics
The x64 compile of this build suffers from performance regressions and is subject to a number of bugs, which also include a crash on startup. The build installs a barebone set of drivers during setup, and additionally lacks a significant majority of the WoW64 compatibility layer, resulting in most x86-based applications not being able to run properly. To achieve better performance, apply the Windows Classic theme.

Hardware Abstraction Layer bugcheck on Checked/Debug compile
Attempting to boot the x64 checked/debug version of this build on a host device that has the Hyper-V hypervisor enabled results in a bug within the Hardware Abstraction Layer's processor feature check, in turn triggering a 0x7E bugcheck. The issue can be worked around by either substituting the  binary with the variant from the Free compile or by disabling Hyper-V  from the host's boot options.