Development of Windows 95

The initial design and planning of Windows 95 can be traced back to around March 1992,[1][2][3] just after the release of Windows 3.1. At this time, Windows for Workgroups 3.11 and Windows NT 3.1 were still in development and Microsoft's plan for the future was focused on Cairo. Cairo would be Microsoft's next-generation operating system based on Windows NT and featuring a new user interface and an object-based file system, but it was not planned to be shipped before 1994 (Cairo would eventually partially ship in July 1996 in the form of Windows NT 4.0, but without the object-based file system, which would later evolve into WinFS).

Simultaneously with Windows 3.1's release, IBM started shipping OS/2 2.0. Microsoft realized they were in need of an updated version of Windows that could support 32-bit applications and preemptive multitasking, but could still run on low-end hardware (Windows NT, requiring 12MB RAM and 75MB disk space, did not). So the development of Windows "Chicago" was started and, as it was planned for a late 1993 release, became known as Windows 93. Initially, the decision was made not to include a new user interface, as this was planned for Cairo, and only focus on making installation, configuration, and networking easier. Windows 93 would ship together with MS-DOS 7.0, offering a more integrated experience to the user and making it pointless for other companies to create DOS clones. MS-DOS 7.0 was in development at that time under the code name "Jaguar" and could optionally run on top of a Windows 3.1-based 32-bit protected mode kernel called "Cougar" in order to better compete with DR-DOS.

The Chicago project was led by Brad Silverberg, who, at that time, was senior vice president of the personal systems division at Microsoft. Microsoft's product plan looked as follows:

Codename Planned release date Description Released as
"Astro"[4] September 1992 Upgrade to MS-DOS 5.0, adding third party tools to surpass DR-DOS 6.0 in features. MS-DOS 6.0
"Winball", "Sparta"[4] October 1992 Windows 3.1 with network support. Windows for Workgroups 3.1
"Jaguar"[4] June 1993 Next major release of real-mode MS-DOS, better integrating with Windows MS-DOS 7.0 (Windows 95 MS-DOS mode)
"Cougar"[4] June 1993 A 32-bit protected-mode MS-DOS kernel based on Windows' 386 enhanced-mode kernel Windows 95 VMM
"Panther"[4] June 1993 The 32-bit Windows subsystem that could run on top of "Cougar" implementing a subset of Windows NT's Win32 API, but a superset of the Win32s API. Windows 95
"Rover"[4] June 1993 Windows for Mobile Computing, based on "Panther" Windows for Pen Computing 2.0/WinPad (unreleased)
NT, NT OS/2, "Razzle" July 1993 A new version of Windows built from the ground up as an operating system for servers and workstations. Windows NT 3.1
"Bombay" December 1993 An update to Windows 3.1. Windows 3.11
"Snowball" [4] February 1994 Windows for Workgroups 3.1 with upgrades. Windows for Workgroups 3.11
"Daytona" September 1994 Successor to Windows NT 3.1. Windows NT 3.5
"Cairo" July 1996 An operating system with an object-based file system and a new user interface shell ported from Windows 95. Partially shipped as Windows NT 4.0, without the file system.
"Nashville" August 1996 A new version of Windows 95 build 999 (Windows 96) was expected to be released, but was not confirmed. Unreleased; partially became Windows Desktop Update

The first version of Chicago's feature specification was finished on September 30, 1992. Cougar was to become Chicago's kernel.

Prior to the official release, the American public was given a chance to preview Windows 95 in the Windows 95 Preview Program. For US$19.95, users were sent a set of 3.5-inch floppy diskettes that would install Windows 95 either as an upgrade to Windows 3.1x or as a fresh install on a clean computer. Users who bought into the program were also given a free preview of The Microsoft Network (MSN), the online service that Microsoft launched with Windows 95. During the preview period Microsoft established various electronic distribution points for promotional and technical documentation on Chicago[5] including a detailed document for media reviewers describing the new system highlights.[5][6] The preview versions expired in November 1995, after which the user would have to purchase their own copy of the final version of Windows 95.

Several Windows 95 betas were released before the final launch:

Build Description Startup Screenshot Desktop Screenshot
Build 58s Build 58s introduced a Start menu prototype. It divided the functions of the Windows 95 Start menu up into three buttons. Future Chicago builds combined these three into the Start button still recognized today.

Build 58s included a new File Manager, Chicago Explorer, which remained relatively unchanged in the initial version of Windows 95 and in Windows NT 4.0. Build 58s still included Program Manager as found in Windows 3.1, although this application was supplemented by the new desktop and taskbar/Start menu designs.

It has a date of August 10, 1993.

This build also introduced shortcuts (Chicago referred to them as Links) and native right click functionality, which Windows 3.1 lacked. It also introduced long file name support.

Build 73g Build 73g is the next leaked build of Windows Chicago with a date of December 2, 1993. It is mostly the same as Build 58s, with a few UI tweaks and a network logon box at startup. Windows Chicago (build 73) boot screen.gif A screenshot of the Windows Chicago build 73 desktop.
Build 81 Build 81 follows build 73g. The date stamp says it is from January 1994. The three start buttons are combined into one. However, the 8.3 filename limit makes the Start Menu item "Accessories" read "access~1". Programs running are only displayed on the taskbar. The briefcase UI was improved. The My Computer item is displayed when opened as :drives, Network as :network, and Control Panel as CONTROLS.
Build 122 Build 122 was the first version of Chicago to define itself as a Beta edition. There is a date stamp of June 9, 1994. This build includes a few minor improvements such as a different type of "Under Construction" background, the arrow being removed from the Start button, and the removal of some Control Panel items. There were also other interface updates: e.g. title of the My Computer, Control Panel, and Network windows are correct. The tips that would appear in the windows actually slide from right to left on the taskbar, starting from the clock and bouncing against the start button a few times. These get reset when opening-then-closing a window.
Build 189 Build 189 is the first version to call itself Windows 95. The date stamp is marked September 21, 1994. The UI has been completely revamped to the final version look&feel, except for few left-overs from Chicago. Start menu also slightly differs from newer builds of Windows 95, as there is actually color along the side.

The background picture shown continued to live on in the final Windows 95 installer.

Build 224 Build 224 is Windows 95 beta 2. Only a date stamp of November 8, 1994, can be found as information on this build.
Build 347 Build 347 is the Windows 95 "Final Beta Release". The build number refers to a German release, but seems to install in English. This version has a date stamp of March 17, 1995. The startup screen from build 347.
Build 468 Build 468 is the May Test Release version of Windows 95, with a date stamp of May 11, 1995. Final startup – dubbed The Microsoft Sound – and shutdown sound made their first appearance. The startup screen from build 468, 480, 490 and 501 (490 and 501 are June test release, but with the same startup screen indicating "June test release" under the Windows 95 logo instead of "May test release").
Build 480 Build 480 is the May Test Release. It was released in two languages: English and German.
Build 490 (Pre-RC1) Build 490 is the first June Test Release dated on June 8, 1995. The build number seems to indicate that this is a pre Release Candidate 1.
Build 501 (RC1) Build 501 is dated at June 21, 1995. It seems to be the final Release Candidate 1.


  1. ^ "Plaintiff's Exhibit 1263" (PDF). Comes v. Microsoft. March 5, 1992.
  2. ^ "Plaintiff's Exhibit 1308" (PDF). Comes v. Microsoft. May 7, 1992.
  3. ^ "Plaintiff's Exhibit 1310" (PDF). Comes v. Microsoft. May 9, 1992.
  4. ^ a b c d e f g "Plaintiff's Exhibit 1285" (PDF). Comes v. Microsoft. April 9, 1992.
  5. ^ a b "Microsoft Windows Chicago Reviewer's Guide" (PDF). p. 282.
  6. ^ Manes, Stephen (July 19, 1994). "PERSONAL COMPUTERS; Microsoft's New System Promises to Fix Glitches". New York Times. The New York Times.

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