Windows Blackcomb

Windows Blackcomb is the original codename of Windows 7 used from 2001-2005, it was later replaced by Windows Vienna. It has the version number 6.1.

Build 2468
First Blackcomb Build. Delt release for Windows 7. Released in April 2001

Build 2472
Pre-Alpha release for Windows 7. Released in May 2001.

Build 2477
Pre-Alpha release for Windows 7. Not leaked. Released in May 2001. Similar to Windows Beta 4.1.

Build 3570
Known to exist from some build strings in later builds, this is considered to be Blackcomb Milestone 1. If such a build existed it would look like Windows XP in exact.

Build 3826 (Milestone 2)
Not leaked, but known to exist from screenshots. Has XP Luna design.

Build 3837 (Milestone 3)
Not leaked, similar to 3826. The about screen is a screenshot called it 'Blackcomb XP Milestone 3'.

Build 3906
The earliest leaked build, compiled on November 10, 2003and leaked on September 2, 2005. This version has the Plex user interface, similarly to Longhorn 3683.

Build 4020 (Milestone 4)
Compiled on February 5, 2003. Looks more like Longhorn 3718.

Build 4106
Compiled on April 4, 2003. Similar to Longhorn M4 builds.

Build 4128
Compiled on April 19, 2003. The first Blackcomb build to introduce the Desktop Composition Engine, it also has a different login screen to 4020 and 4106.

Build 4137
Screenshots have been seen, it seems to look like 4128 but is unleaked.

Build 4196 (Milestone 5)
Compiled on May 20, 2003 and leaked on June 16, 2003. Included the experimental Fire Classic visual style.

Build 4204
Compiled on June 1, 2003, also includes Fire Classic.

Build 4257
Compiled on June 28, 2003. This build was considered to be too unstable to be installed and despite the build being leaked, there isn't much known about it.

Build 4276
Alpha release for Windows 7. Compiled on July 14, 2003, this build defaults to XP Luna UI and Plex/Fire Classic can only be enabled in the registry. This build only surfaced on January 19, 2017.

Build 4303 (Milestone 6)
Compiled on August 2, 2003. This was one of the last known builds to include Plex as later on the visual styles would default to Fire Classic/Ice Classic/Slate/Jade.

Build 4336 (PDC 2003)
Compiled on October 17, 2003 and leaked on October 20, 2003. Similar to Longhorn 4051.

Build 4357 (WinHEC 2003)
Compiled on April 25, 2003 and leaked on May 2004. Similar to Longhorn 4074.

Build 4383
Compiled on May 6, 2004 and leaked on November 10, 2004. Similar to Longhorn 403.

Build 4393
Compiled on August 19, 2004. Similar to Longhorn 4093.

Build 4542 (WinHEC 2005)
Compiled on April 1, 2005. Similar to Longhorn 5048.

Build 4573 (PDC 2005)
Last Blackcomb Build. Compiled on August 29, 2005. Similar to Windows Vista Beta 1.