Development of Windows 95

The initial design and planning of Windows 95 can be traced back to around March 1992, 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. At this point, Microsoft's strategy was to have a next generation, high-end OS based on Windows NT, namely, Cairo, and a low-end, consumer-focused one as an evolution of Windows 3.1. The latter strategy was to develop a 32-bit underlying kernel and filesystem with 32-bit protect mode device drivers in Windows for Workgroups 3.11, to be used as the basis for the next version of Windows, code named "Chicago." Cairo would be Microsoft's next-generation operating system based on Windows NT featuring a new user interface and an object-based file system, but it was not planned to be shipped before 1994 (Cairo would never be shipped, however, although elements from the Cairo project would eventually ship in late July 1996 in Windows NT 4.0, 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 12 MB RAM and 75 MB disk space, did not). Initially, the "Chicago" team did not know how the product would be packaged. Initial thoughts were there might be two products, MS-DOS 7, which would just be the underlying OS, an evolution of the Windows for Workgroups 3.11 kernel, with a character mode OS on top, and a fully integrated graphical Windows OS. But soon into the project, the idea of MS-DOS 7 was abandoned and the decision was made to develop only an integrated graphical OS Windows "Chicago."

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"	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"	October 1992	Windows 3.1 with network support.	Windows for Workgroups 3.1
"Jaguar"	June 1993	Next major release of real-mode MS-DOS, better integrating with Windows	MS-DOS 7.0 (Windows 95 MS-DOS Mode)
"Cougar"	June 1993	A 32-bit protected-mode MS-DOS kernel based on Windows' 386 enhanced-mode kernel	Windows 95 VMM
"Panther"	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"	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"	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.	Elements of Cairo were shipped in Windows NT 4.0, minus the object-based file system.
"Cleveland", "Nashville"	August 1996	A new version of Windows 95 (build 999, also referred to as Windows 96) focusing on the tight integration of Windows and Internet Explorer was expected to be released, but has not been confirmed.	Cancelled; codename reused for Windows Desktop Update, which shipped with most of Nashville's features.

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 including a detailed document for media reviewers describing the new system highlights. 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
Cougar build 28	Windows Cougar build 28 is a fake Windows build, supposedly part of the Cougar project which was said to predate Chicago. The build itself is just a modified Windows for Workgroups 3.11, while the Cougar codename was actually used for the 32-bit protected-mode kernel introduced with Chicago and not an entirely separate OS. According to the NFO file included, it was shared by Battler (at the time known as OBrasilo) on the Euro-Asian Beta Group in 2008. It can still be found online to this day.
Cougar build 33	Windows Cougar build 33 is an unconfirmed pre-Chicago build that was mentioned in the setup file for build 58s, though whether it actually exists is unknown.
Build 31	Build 31 is an unconfirmed build of Windows 95. Only a few screenshots of it exists, and their authenticity is unknown.
Build 34	Build 34 is the earliest confirmed build of Windows 95. OLDSETUP.INF is a remnant of previous Chicago builds, together with SETUP31.VER, SETUP31.EXE, SETUP31.INF and OLDSETUP.BAT. It gives a pretty good insight into the installation process of pre-58s builds. These files indicate that early Chicago setup was merely a rebranded Windows 3.1x setup and did not include major changes or new features. The new setup, as seen in build 58s, was likely introduced as part of the M4 stage. Early leaked builds also still include the old Windows 3.1x-like boot screen, SYSLOGO.RLE, which is also a leftover from previous builds and may have been used in build 34. There is also a video claiming to show this build by user George Wolfowitz. As this build remains unleaked, the authenticity of the video can't be confirmed. Some observations from the video: "Personal" and "Programs" folders on the desktop are only links to these folders. The Help button icon is from build 58s, but the System icon (a computer) is the same as in the Usability Testing Builds. The Help menu is missing some items. The boot screen shown is the already mentioned SYSLOGO.RLE, also found in later builds (though no longer used). "About Chicago" dialog properly displays user and company information, unlike build 58s which displays placeholder strings. This could suggest the setup used in this build asks the user for username and organization information. The Control Panel (CONTROLS.SYS) title bar icon is different. Three Control Panel items are missing, while some others have different icons. It's worth noting that the uploader has not been active since the video was uploaded, casting suspicion on their intentions with this video.
Build 40	Build 40 is a supposed early build of Windows 95. Former BetaArchive member KenOath posted several screenshots, but their authenticity remains disputed by some due to several inconsistencies within them. There was also a fake copy floating around, but it is unrelated to KenOath. It was made with files from various builds (mostly build 58s), supposedly even from the real build 40, but this was never proven to be true. It remains available online to this day. There are in fact two files (CONTROL.EXE and PROGMAN.EXE) in build 58s with version number 4.00.40, but this does not necessarily mean they come from build 40.
Build 40e	Build 40e is one of the earliest confirmed builds of Windows 95, mentioned in internal Microsoft e-mails from early April 1993. The e-mails discuss issues with Microsoft's Visual C++ running on this build. Apparently, the Visual C++ development team had access to at least part of Windows 3.1 source code and used an undocumented private function in Shell VxD to create their virtual machines. Under Windows 3.1x this worked fine, but on Chicago build 40e it doesn't, because the Windows-specific shell services were moved into a separate VxD named WShell. According to the developer describing the issue, this was done because a standalone MS-DOS 7.0 release was originally planned to be released alongside Windows 95, and those plans persisted well into 1993. It's also worth mentioning this build was apparently recompiled several times, as indicated by the letter e next to the build number, and may have been one of the pre-build 58s external releases.
Build 56	Build 56 is a fake build of Windows 95. It was uploaded to BetaArchive FTP server on 25 January 2009, and then was removed on 1 June 2012, along with builds 73 and 78. These builds were said to be made with files from various other builds and modified to report a different version number. This build is very similar in appearance to build 58s, but with some minor differences, the most notable are a couple of different icons.
Build 57	Build 57 is mentioned in the file MPPRINT.C from Chicago build 58s SDK, along with build 58g. // Build 58g chokes on LoadLibrary(), so we'll have to disable it #if 0 // workaround because LoadLibrary() needs explicit .DRV extension in Build 57 strcpy(szDriverBuf, szDriver); The file FREECELL.EXE from build 58s also has the 4.00.57 version number.
Build 58g	Build 58g is a unreleased build. It is mentioned in the file MPPRINT.C from build 58s SDK.
Build 58j	Build 58j is an unleaked build of Windows 95. A total of 16 files with the 4.00.58j version number were found in build 58s. Judging by the file dates, it would have been compiled in mid-July 1993.
Build 58s	Build 58s was the first available build of Chicago, dated August 10, 1993. Other earlier builds are known to exist. It 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. 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 61	Build 61 is mentioned in the file EPSFILES.DOC from build 116's DDK. This file contains several Encapsulated Postscript files. They were created in Paintbrush in build 61 of Chicago. The EPS file created with version 3.55 of the old driver was done in Windows for Workgroups 3.11. Page 3 contains EPS files that were created using a level 2 PostScript printer.
Build 70	Build 70 was mentioned in the file SETUPC.INF from Chicago builds 73f and 73g. [winbase.inis] system.ini,boot,,"comm.drv=comm.drv" system.ini,boot,,"user.exe=user.exe" system.ini,boot,,"gdi.exe=gdi.exe" system.ini,boot,,"sound.drv=sound.drv" system.ini,boot,,"dibeng.drv=dibeng.dll" system.ini,386Enh,"device=fakeide.386", ;remove PRE-RELEASE ONLY starting bld 70
Build 73	Build 73 is a fake build based on build 73g. It was uploaded to the BetaArchive FTP server and removed on 1 June 2012, along with builds 56 and 78, though it can still be found online on various other websites.
Build 73f	Build 73f is a Milestone 5 (Preliminary Development Kit 2) build of Windows 95. It was found by BetaArchive user sunnyblueman in July 2014 along with builds 99 and 116, then uploaded to the BetaArchive FTP by the same user on 2 August 2014. It is nearly identical to build 73g. The main difference is that this is an internal build and thus includes an internal version of the WinBug utility, while build 73g was released to external testers and thus features a different WinBug. It is safe to assume earlier compiles of this build (73a through 73e) also exist. There are notable changes in this build compared to build 58s. Many aspects of Windows were ported to 32-bit, including the Cabinet shell (as stated by the new filename, CAB32.EXE). The taskbar no longer functions as a folder by default. Instead, it now displays the running apps in a similar way to the modern taskbar. This build introduces the Briefcase special folder, which is meant to sync files between itself and another folder. It is also the first build to feature the "safe to shutdown" screen, serving as a reminder of when to turn off the PC without risk of possible data loss. Since this build's installation media also comes with a SDK, it can be used to switch to a checked/debug compile of this build.
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.
Build 78	Build 78 is a fake build, which was uploaded by BetaArchive member Battler (at the time also known as OBrasilo). It was later confirmed to be a modified version of build 73g. It was removed from the BetaArchive FTP server on 1 June 2012, along with builds 56 and 73.
Build 81	Build 81 follows build 73g. The date stamp still says that it's from November 1993. 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 84	Build 84 is a build of Windows 95. It is mentioned in the file ICONEXT.C from the Windows NT 4.0 source code. // // BUGBUG: WideCharToMultiByte does not work on build 84. //
Build 86	Build 86 is mentioned in the file DEFCLSF.C from build 116's SDK. // BUGBUG: remove this for build 86 STDAPI Shell_CreateDefClassObject(REFIID riid, LPVOID FAR* ppv, LPFNCREATEINSTANCE lpfnCI, UINT FAR * pcRefDll, REFIID riidInst) { MessageBeep(0); // DebugMsg(DM_TRACE, "Shell_CreateDefClassObject: obsolete, use SHCreateDefClassObject"); return SHCreateDefClassObject(riid, ppv, lpfnCI, pcRefDll, riidInst); }
Build 87	Build 87 is an unleaked build.
Build 89	Build 89 is a Milestone 6 build. It is mentioned in the file XFDSPDLG.C from the Windows NT 4.0 source code. // As of 14-Apr-94 (build 89) still doesn't work // As of the May Beta, it did work
Build 89e	Build 89e is a Milestone 6 build of Windows 95, which was shared on BetaArchive on 5 May 2020. As indicated by the build number, it is a recompile of build 89. Although very similar to the next available build (build 90c), there are some minor visual differences between them. This is also the earliest available build to include the redesigned Microsoft Paint program, though it's still called "Paint Brush" in the About dialog.
Build 90	Build 90 is a Milestone 6 build. It is mentioned in the file MSDOS.INF from build 99.
Build 90b	Build 90b is a Milestone 6 build of Windows 95. This build is mentioned in the VER command from build 90c.
Build 90c	Build 90c is an internal Milestone 6 build of Windows 95, which was originally scene-leaked and considered lost, but was later found and uploaded to BetaArchive by Battler on 17 November 2017. It is a re-compile of builds 90 and 90b, based on the letter following the build number. In general, this build has a very similar feature set to build 89e, including all of the bugs from the previous build.
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.
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.
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.