Windows Calico

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Windows Calico is a Microsoft operating system, designed for older PCs that can't run Windows Vista, 7, 8, 8.1, or 10. It was released in April 2019, and is the successor to Windows XP LTS (Long Term Support), which was released in 2014. Its early builds are based off Windows 2000 Datacenter Server.


Earliest builds

Before Windows Calico development started, there was Windows NT Embedded 1995. In 1996 Microsoft released a build of Windows NT Embedded 1995 codenamed Calico.


Later, the build is renamed from "Calico" to "Felicity". Due to Windows NT 5.0 and development of Windows 98 it is cancelled and original build was merged in order to develop Windows Memphis. The release intended to focus on a tighter integration between Windows and Internet Explorer, in order to better compete with Netscape Navigator. After the deal with MTM it is reset with a Plus pack, an early version of Outlook and a new version of Internet Explorer. Later, the reset build was merged with NT project "Silvestris" to form Windows Codename: Calico.


During development of Windows NT 5.0 Microsoft made a deal with MTM Enterprisss Inc. to collaborate on a NT Project to make a variation of NT kernel with key features of MTM OS and TVS OS kernels, to make a MTM-like NT project (MTM-like means OS behaving in a similar manner to or being compatible to either MTM OS, TVS OS or both).

In late 1996, they created the Windows codename: Silvestris build 777.7, which is updated version of Windows 5.0 Beta 1. It introduced logon screen, firewall, new start menu, start screen and Internet Explorer 7.7. It is planned to be released in July 7 1997. Several Silvestris builds were part of early Windows NT 5.0 builds. However, the project proved to be too ambitious. Later builds featured MTM OS-esque features. They merged reset Windows Felicity and Windows codename Silvestris to form Windows Codename: Calico in May 1997.

Calico phase 1

In 1997, Windows Calico was formed, and planned to be released in mid 1999. However,due to builds of Windows 2000 (NT 5.0), which was released three days before first build of Beta 3, it is updated. Build 1111.1 It introduced Microsoft Office 1999, Microsoft Dream Browser, and Emergency mode. The last build known is build 1200.5.

Calico phase 2


The Odyssey document confirms there would be new variantion of Windows Server 2000. Later, it would given a codename Calico Server. However, later documents renamed Calico Server to just Calico. As stated in confidental document, Delta is originally planned as a Windows Server 2000 variation. This changed in August 5 1999.


Five days after the release of Windows 2000, Windows Calico Server was renamed to Windows Codename Calico by adding Windows 2000 Datacenter features to the Windows Calico features. On build 2000.0 there was a debate when is this actual pre-alpha of Windows Calico or post RTM build of Windows 2000 Datacenter Server. However, the only exception of this combined build is the rare boot screen with "Datacenter Server" instead of "Server Family". This means the beta testers and users to not confusing the build with the Server and Advanced Server ones. The "SD" in the build tag refers to a new code management system that Microsoft was developing ("Source Depot").  Build 2004.6 has bug fixes and many security patches, featuring some elements from early Windows Chicago. Build 2009.5 has elements from Plus for Windows 95 and 98, Microsoft Plus! Game Pack: Cards & Puzzles, Microsoft Plus! for Kids!, Windows For Pen Computing 2.0 ,WinG . First appearance of the word "Calico" is in build 2009B.8. In build 2012.8 it introduces startup and shutdown screens.  At WinHEC in January 31 2000, Microsoft officially announced and presented an early build of Calico (build 2020.4), focusing on a new modularized architecture, built-in CD burning, fast user switching, fast boot, and updated versions of the digital media features and other features introduced by ME, also featuring OOBE. Build 2020.9 introduced logoff screen. At build 2072.8 (A.K.A Pre-Developer Release) bootscreen "Microsoft Windows 2000 Datacenter Server" was renamed to "Microsoft Codename: Calico" dropping "Datacenter Server" because this Windows version was meant to succeed Whistler (XP), not Whistler Server (Server 2003). At build 2022.9 it introduced white version of Windows Standard theme, later to be known as "Prototype". Build 2042.5 imports features from PocketPC 2000 and Windows CE 3.0 . Build 2051.2 has features from Windows NT 4.0 Terminal Server. Build 2054.6 introduced new startup and shutdown sounds. The startup sound is reversed Windows 2000 build 2000 startup. The shutdown sound is chime assemble with turning and transforming into Windows 98 startup sound, ending with it's RTM shutdown sound. The logon sound is Windows CE startup and the logoff sound is Windows 2000 build 2000 shutdown sound, with mixture of it's RTM version. It also introduced updated version of 98 error,notify and ding. It also introduced new sound: balloon sound(also introduced balloon), excalmation sound, critical sound,asterisk sound, battery low sound and battery critical sound. It keep the start-up and shutdown sounds of previous versions. Build 2062.6 introduced VoiceSearcher. Build 2069.6 introduces MS-DOS real mode and parts from Windows 9x kernel, along with Microsoft Works, Microsoft Money preinstalled. MS contiunes development of Neptune and Odyssey, however, puts it on held as he stated they have same features with Codename Calico. Build 2098.4 features Neptune Activity Centre ported from Neptune, later was renamed to Activity Centre during the development. Developer release was released in March 9 2000, build 2143.9 ,the Windows 2000 Server logo was replaced by normal Windows 2000 logo. Prealpha version was released in May 7 2000, build 2176.7. Techincal Alpha was released in June 1 2000, build 2200.0 . Alpha version was released in June 5 2000,build 2222.2. It introduces variety of features, such as sidebar, modified version of TaskGallery. Pre-Beta version was released in June 23 2000, build 2230.8 . Omega-7 is released in June 17 2000, build 2245.7. introducing Superbar for Prototype, as an hidden extra. It featured updated version of Start button, similar to start button Whistler 2296 build . Technical Beta was released in July 8 2000,build 2255.6 . Beta 1 was released in May 13 2001, build 2311.5. Beta 1.5 was released in May 17 2001, build 2375.6 Pre-Beta 2 Fork is released in May 19 2001, build 2378.6. Beta 2 was released in June 31 2001, build 2400.0. with start button from Whistler 2257. Beta 2.5 was released in September 1 2001, build 2419.8. Beta 2.5.7 was released in September 10 build 2428.5. Beta 2.6 was released in September 17 2001, with start button from Whistler build 2250. The last build before official name of the project has revealed is build 2489.9., with Xbox app preinstalled. Then Windows Calico will be known as a new name. The choice began on September 15 2001 and ended on September 20 2001. There were three choices.

Calico phase 3

Originally, Windows Delta should named choice of either "Windows.NET" or "Windows 2001" or even "Windows NT 5.15". The most popular choice was Windows.NET. Before Windows Calico was confirmed, Bill Gates think, that none of them will be used, due to changed plan. The plan changed because of the OS was not even fully finished for year 2001, server has not improved and Windows Codename Calico is being different to Windows 2000. Bill Gates states that calico cats are his favorite animals. Choice is calico-colored Windows flag with text or the text by itself with no Windows flag. Most of employees choosed the logo, since the OS was made with partnership and friendship of Kadishenware and OMV. Tev Hanamadski agreed. October 3 2001, Windows Calico Beta 2.7 was released, build 2490.1. Beta 2.9 was released in October 10 2001, build 2500.0. Beta 3 was released in October 29 2001, build 2533.8. Final Beta Release was released in November 23 2001, build 2540.4. The last build ever to include the word "Codename" is 2540.0. Final Beta Release include Luna, Royale, Zune, Embedded, Watercolor, and Chartreuse Mongoose themes, other than Prototype theme. Release Preview was released in December 9 2001, build 2555.5. Community Technology Preview was release in December 12 2001, build 2557.9. Release Candidate 0 was released in December 13 2001, build 2560.9. Release Candidate 1 was released in December 22,2001,build 2575,9. Release Candidate 2 was released in December 28 2001, build 2590.6. Pre-RTM build of Windows Calico was released in January 3 2002 build 2591.3. RTM Escrow build was released in January 7 2002, build 2592.0. Public Testing build was released on January 8 2002, build 2592.5. Stability and Security Testing was released on January 9 2002, build 2592.9 of Windows Calico was released in January 10 2002, build 2593.5. Another build of Windows Calico was released in January 19 2002, build 2595.7. Release to web of Windows Calico was released at January 24 2002,build 2599.1. Windows Calico next build officially released at February 22 2002, build 2600.0. After this release, Microsoft and MTM end their partnership.

Calico phase 4

See /Phase 4

Calico phase 5

See /Phase 5

Calico phase 6

See /Phase 6

(More TBA)

Theme Packs

Prototype Theme

Windows Classic

Windows Aero


Prototype - A theme used for the OS

Sidebar - A sidebar, similar to the one, used in Longhorn and Windows Vista, haves features mixed with these from Sideshow.

Transparent - Taken from Windows Zeus, allows user to turn the taskbar and sidebar into transparent.


  • So far, Windows Calico is the longest Windows version ever developed. If one counts Windows NT Embedded 1995, it makes it even longer.
  • It was unknown if there are any reset build of Windows Felicity. Beta-testers believe, that there are some. There are build 4.10.1055 and 4.10.1167. It is unknown if they are real or fake.
  • Before the name is revealed, Beta-testers give a new name for new Windows version. The fan-name is Windows XPSE. (Coincidentally, Windows Calico is Windows XPSE , just not the beta testers excepted)
  • It was unknown what build is concept build of Windows Calico. Until 2010, Beta-testers analysed that the concept version of the build is build 2406.8.
    • Windows Calico is a sister/brother to Windows XP
    • The features of Windows Powered were added to Windows Calico during development.